Automatic Extended Route Optimization (AERO)
draft-templin-6man-aero3-57
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| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Author | Fred Templin | ||
| Last updated | 2026-02-26 | ||
| Replaces | draft-templin-intarea-aero2 | ||
| RFC stream | (None) | ||
| Intended RFC status | (None) | ||
| Formats | |||
| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
| RFC Editor Note | (None) | ||
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| Send notices to | (None) |
draft-templin-6man-aero3-57
Network Working Group F. L. Templin, Ed.
Internet-Draft Boeing Technology Innovation
Intended status: Standards Track 25 February 2026
Expires: 29 August 2026
Automatic Extended Route Optimization (AERO)
draft-templin-6man-aero3-57
Abstract
This document specifies an Automatic Extended Route Optimization
(AERO) and mobility service for IP internetworking over Overlay
Multilink Network (OMNI) Interfaces. AERO/OMNI use IPv6 Neighbor
Discovery (IPv6 ND) control plane messaging over the OMNI virtual
link to support secured network admission and OMNI link forwarding.
Flow-based secure multilink path selection, multinet traversal,
mobility management, multicast forwarding, multihop operation and
route optimization are naturally supported through dynamic neighbor
cache updates. AERO is a widely-applicable service well-suited for
air/land/sea/space secure global mobile Internetworking applications
including aviation, intelligent transportation systems, mobile end
user devices, space exploration and many others.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 29 August 2026.
Copyright Notice
Copyright (c) 2026 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 17
4. Automatic Extended Route Optimization (AERO) . . . . . . . . 17
4.1. AERO Node Types . . . . . . . . . . . . . . . . . . . . . 18
4.2. The AERO Service over OMNI Links . . . . . . . . . . . . 19
4.2.1. AERO/OMNI Reference Model . . . . . . . . . . . . . . 19
4.2.2. AERO Addressing . . . . . . . . . . . . . . . . . . . 23
4.2.3. AERO Overlay Routing System . . . . . . . . . . . . . 23
4.2.4. Segment Routing Topologies (SRTs) . . . . . . . . . . 24
4.3. OMNI Interface Characteristics . . . . . . . . . . . . . 25
4.4. OMNI Interface Initialization . . . . . . . . . . . . . . 28
4.4.1. AERO Gateway Behavior . . . . . . . . . . . . . . . . 28
4.4.2. AERO Proxy/Server and Relay Behavior . . . . . . . . 28
4.4.3. AERO Client Behavior . . . . . . . . . . . . . . . . 29
4.5. OMNI Interface Neighbor Cache Maintenance . . . . . . . . 29
4.5.1. AERO/OMNI Control Plane Messages . . . . . . . . . . 31
4.5.2. OMNI Neighbor Window Synchronization . . . . . . . . 33
4.6. OMNI Interface Encapsulation and Fragmentation . . . . . 33
4.7. OMNI Interface Decapsulation . . . . . . . . . . . . . . 35
4.8. OMNI Interface Data Origin Authentication . . . . . . . . 36
4.9. OMNI Interface MTU . . . . . . . . . . . . . . . . . . . 37
4.10. OMNI Interface Forwarding Algorithm . . . . . . . . . . . 37
4.10.1. Client Forwarding Algorithm . . . . . . . . . . . . 39
4.10.2. Proxy/Server and Relay Forwarding Algorithm . . . . 40
4.10.3. Gateway Forwarding Algorithm . . . . . . . . . . . . 43
4.11. OMNI Interface Error Handling . . . . . . . . . . . . . . 44
4.12. AERO Mobility Service Coordination . . . . . . . . . . . 47
4.12.1. AERO Service Model . . . . . . . . . . . . . . . . . 47
4.13. AERO Address Resolution, Multilink Forwarding and Route
Optimization . . . . . . . . . . . . . . . . . . . . . . 49
4.13.1. Multilink Address Resolution . . . . . . . . . . . . 51
4.13.2. Multilink Forwarding . . . . . . . . . . . . . . . . 57
4.13.3. Mobile Ad-hoc Network (MANET) Forwarding . . . . . . 64
4.13.4. AERO Route Optimization . . . . . . . . . . . . . . 66
4.14. Neighbor Unreachability Detection (NUD) . . . . . . . . . 69
4.15. Mobility Management and Quality of Service (QoS) . . . . 69
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4.15.1. Registering Link-Layer Information Changes . . . . . 70
4.15.2. Deactivating Existing Links . . . . . . . . . . . . 71
4.15.3. Moving Between Proxy/Servers . . . . . . . . . . . . 71
4.15.4. Mobility Update Messaging . . . . . . . . . . . . . 73
4.15.5. Accommodating Path Changes . . . . . . . . . . . . . 74
4.16. Multicast . . . . . . . . . . . . . . . . . . . . . . . . 74
4.16.1. Source-Specific Multicast (SSM) . . . . . . . . . . 75
4.16.2. Any-Source Multicast (ASM) . . . . . . . . . . . . . 76
4.16.3. Bi-Directional PIM (BIDIR-PIM) . . . . . . . . . . . 77
4.17. Operation over Multiple OMNI Links . . . . . . . . . . . 77
4.18. Transition/Coexistence Considerations . . . . . . . . . . 78
4.19. Proxy/Server-Gateway Bidirectional Forwarding
Detection . . . . . . . . . . . . . . . . . . . . . . . 78
4.20. Time-Varying MNPs . . . . . . . . . . . . . . . . . . . . 79
5. Implementation Status . . . . . . . . . . . . . . . . . . . . 79
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 79
7. Security Considerations . . . . . . . . . . . . . . . . . . . 80
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 82
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 84
9.1. Normative References . . . . . . . . . . . . . . . . . . 84
9.2. Informative References . . . . . . . . . . . . . . . . . 86
Appendix A. Non-Normative Considerations . . . . . . . . . . . . 93
A.1. Implementation Strategies for Route Optimization . . . . 93
A.2. Implicit Mobility Management . . . . . . . . . . . . . . 93
A.3. Direct Underlying Interfaces . . . . . . . . . . . . . . 94
A.4. AERO Critical Infrastructure Considerations . . . . . . . 94
A.5. AERO Server Failure Implications . . . . . . . . . . . . 95
A.6. AERO Client / Server Architecture . . . . . . . . . . . . 95
Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 97
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 98
1. Introduction
Automatic Extended Route Optimization (AERO) fulfills the
requirements of route optimization [RFC5522] and Distributed Mobility
Management (DMM) [RFC7333] for air/land/sea/space secure global
mobile Internetworking applications including aeronautical
networking, intelligent transportation systems, home network users,
enterprise mobile device users, space exploration and many others.
AERO employs the Overlay Multilink Network Interface (OMNI)
[I-D.templin-6man-omni3] with its Non-Broadcast, Multiple Access
(NBMA) virtual link model.
The OMNI link is an adaptation layer virtual overlay manifested by
IPv6 encapsulation over a network-of-networks concatenation of
underlay Internetworks. Nodes on the link can exchange original IP
packets as single-hop neighbors; both IP protocol versions (IPv4 and
IPv6) are supported. The OMNI Adaptation Layer (OAL) supports
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multilink operation for increased reliability and path optimization
while providing fragmentation and reassembly services to support
performance optimization and Maximum Transmission Unit (MTU)
diversity. This specification provides a route optimization and
mobility service architecture companion to the OMNI specification.
The AERO service connects Clients as OMNI link end systems via Proxy/
Servers and Relays as intermediate systems; AERO further employs
Gateways that interconnect diverse Internetworks as OMNI link
segments through OAL forwarding at a layer below IP. Each node's
OMNI interface supports the operation of IPv6 Neighbor Discovery
(IPv6 ND) [RFC4861] as the mobility service control message protocol.
A Client's OMNI interface can be configured over multiple underlay
interfaces, and therefore appears as a single interface with multiple
underlay addresses. These underlay addresses are subject to change
due to mobility and/or multilink fluctuations, with changes
propagated by ND messaging the same as for any IPv6 link.
Clients engage the AERO service according to either the "on-link" or
"off-link" models for IPv6 Neighbor Discovery over OMNI links as
discussed in [I-D.templin-6man-omni3]. For destinations that match
an on-link prefix, the Client performs address resolution and
neighbor unreachability detection as a network layer function that
requires IPv6 ND messaging and neighbor cache state coordination
between the network and adaptation layers. For destinations that
match an off-link prefix, the Client forwards packets to a virtual
router function within the OMNI interface. The OMNI interface then
performs IPv6 ND messaging and neighbor state management as an
adaptation layer service without disturbing the network layer.
AERO provides a secure virtual link management service where mobile
node Clients use Proxy/Servers acting as proxys and/or designated
routers while correspondent nodes on foreign networks use any Relay
on the link for efficient communications. Foreign network
correspondent nodes forward original IP packets destined to other
AERO nodes via the nearest Relay, which forwards them through the
cloud. Mobile node Clients discover shortest paths to OMNI link
neighbors through AERO route optimization. Both unicast and
multicast communications are supported.
Correspondent nodes on foreign networks configure IP addresses from
Foreign Network Prefixes (FNPs) advertised by Relays. Mobile node
Clients register Mobile Network Prefixes (MNPs) with Mobility Anchor
Point (MAP) Proxy/Servers to support global mobile Internetworking.
AERO Gateways peer with Proxy/Servers in a secured private BGP
overlay routing instance to establish a Segment Routing Topology
(SRT) virtual spanning tree over the underlay Internetworks of one or
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more disjoint administrative domains concatenated as a single unified
OMNI link. Each OMNI link instance is characterized by a set of
Mobility Service Prefixes (MSPs) common to all mobile nodes and from
which MNP sub-prefixes are derived. Relays provide an optimal route
from correspondent nodes on foreign links/networks to mobile or fixed
nodes on the local OMNI link. From the perspective of underlay
Internetworks, each Relay appears as the source of a route to the
MSP; uplink traffic to mobile nodes is therefore naturally routed to
the nearest Relay.
AERO operates over OMNI links that span private-use Internetworks
and/or the global public IPv4 and IPv6 Internets. In both cases,
Clients may be located behind Network Address Translators (NATs) on
the path to their associated Proxy/Servers and/or peers. A means for
supporting robust NAT traversal while avoiding "triangle routing" and
critical infrastructure traffic concentration is therefore provided
through a service known as route optimization.
AERO assumes the use of PIM Sparse Mode in support of multicast
communication. In support of Source Specific Multicast (SSM) when a
Mobile Node is the source, AERO route optimization ensures that a
shortest-path multicast tree is established with provisions for
mobility and multilink operation. In all other multicast scenarios
there are no AERO dependencies.
AERO provides a secure aeronautical Internetworking service for both
manned and unmanned aircraft, where the aircraft is treated as a
mobile node (MN) that can connect airborne Internet of Things (IoT)
sub-networks. AERO is also applicable to a wide variety of other use
cases. For example, it can be used to coordinate the links of mobile
nodes (e.g., cellphones, tablets, laptop computers, etc.) that
connect into a home enterprise network via public access networks
with Virtual Private Network (VPN) or open Internetwork services
enabled according to the appropriate security model. AERO also
supports terrestrial vehicular, urban air mobility and mobile
pedestrian communication services for intelligent transportation
systems [RFC9365]. Other applicable use cases including home and
small office networks, enterprise networks and many others represent
additional large classes of potential AERO/OMNI users.
Together with OMNI, AERO supports secured optimal routing for the "6
M's of Modern Internetworking", including:
1. Multilink - a mobile node's ability to coordinate multiple
diverse underlay data links as a single logical unit (i.e., the
OMNI interface) to achieve the required communications
performance and reliability objectives.
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2. Multinet - the ability to span the OMNI link over an end to end
topology connecting multiple diverse administrative domain
network segments while maintaining seamless communications
between mobile Clients and correspondents such as air traffic
controllers, fleet administrators, other mobile Clients, etc.
3. Mobility - a mobile node's ability to change network points of
attachment (e.g., moving between wireless base stations) which
may result in an underlay interface address change, but without
disruptions to ongoing communication sessions with peers over the
OMNI link.
4. Multicast - the ability to send a single network transmission
that reaches multiple nodes belonging to the same interest group,
but without disturbing other nodes not subscribed to the interest
group.
5. Multihop - a mobile Client peer-to-peer relaying capability
useful when multiple forwarding hops between peers may be
necessary to reach a target peer or an infrastructure access
point connection to the OMNI link.
6. (Performance) Maximization - the ability to exchange packets of
all sizes between peers without loss due to a link size
restriction, and to adaptively adjust packet sizes to maintain
the best performance profile for each independent traffic flow.
The following numbered sections present the AERO specification. The
appendices at the end of the document are non-normative.
2. Terminology
The terminology in the normative references applies; especially, the
OMNI specification terminology [I-D.templin-6man-omni3] and the IPv6
Neighbor Discovery (IPv6 ND) [RFC4861] node variables, protocol
constants and message types (including Router Solicitation (RS),
Router Advertisement (RS), Neighbor Solicitation (NS), Neighbor
Advertisement (NA), unsolicited NA (uNA) and Redirect) are cited
extensively throughout. AERO further introduces a new control
message termed "Multilink Pilot (MP)" that consists of an ordinary IP
packet for a flow with an OMNI option trailer. MP messages are used
to control adaptation layer functions only and are never exposed to
the network layer.
Throughout the document, the simple terms "(Proxy/)Client", "Proxy/
Server", "Gateway" and "Relay" refer to "AERO/OMNI (Proxy/)Client",
"AERO/OMNI Proxy/Server", "AERO/OMNI Gateway" and "AERO/OMNI Relay",
respectively. Capitalization is used to distinguish these terms from
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other common Internetworking uses in which they appear in lower case,
and implies that the node in question both configures an OMNI
interface and engages the OMNI Adaptation Layer (OAL).
The terms "All-Routers multicast", "All-Nodes multicast", "Solicited-
Node multicast" and "Subnet-Router anycast" are defined in [RFC4291].
The term "IP" refers generically to either Internet Protocol version
(IPv4 [RFC0791] or IPv6 [RFC8200]) for specification elements that
apply equally to both.
The terms "application layer (L5 and higher)", "transport layer
(L4)", "network layer (L3)", "(data) link layer (L2)" and "physical
layer (L1)" are used consistently with common Internetworking
terminology, with the understanding that reliable delivery protocol
users of UDP are considered as transport layer elements. The OMNI
specification further introduces an "adaptation layer" positioned
below the network layer but above the link layer, which may include
physical links and Internet- or higher-layer tunnels. A (network)
interface is a node's attachment to a link (via L2), and an OMNI
interface is therefore a node's attachment to an OMNI link (via the
adaptation layer).
The following terms are defined within the scope of this document:
IPv6 Neighbor Discovery (IPv6 ND)
a control message service for coordinating neighbor relationships
between nodes connected to a common link. AERO uses the IPv6 ND
messaging service specified in [RFC4861] in conjunction with the
OMNI extensions specified in [I-D.templin-6man-omni3].
IPv6 Prefix Delegation (IPv6 PD)
a networking service for delegating IPv6 prefixes to nodes on the
link. AERO nodes apply the IPv6 PD service provided by DHCPv6
[RFC8415] [RFC9762] in conjunction with OMNI interface IPv6 ND.
GUA, ULA, LLA, MLA
A Globally-Unique (GUA), Unique-Local (ULA) or Link-Local (LLA)
Address per the IPv6 addressing architecture [RFC4193] [RFC4291],
or a Multilink-Local Address (MLA) per [I-D.templin-6man-mla].
IPv4 prefixes other than those reserved for special purposes
[RFC6890] are also considered as GUA prefixes.
L3
The Network layer in the OSI reference model, also known as "layer
3" or the "IP layer". The Network layer engages the Adaptation
layer via OMNI interfaces.
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Adaptation layer
An IPv6 encapsulation and fragmentation mid-layer that adapts L3
to a diverse collection of underlay interfaces. The adaptation
layer then engages an underlay network that performs UDP/IP, IP,
or NULL encapsulation for transmission over underlay interface
attachments to L2 media.
L2
The Data Link layer in the OSI reference model, also known as
"layer 2" or "link layer".
Access Network (ANET)
a connected network region (e.g., an aviation radio access
network, corporate enterprise network, satellite service provider
network, cellular operator network, residential WiFi network,
etc.) that connects Clients to the Mobility Service over the OMNI
link. Physical and/or data link level security is assumed and
sometimes referred to as "protected spectrum" for wireless
domains. Private enterprise networks and ground domain aviation
service networks may provide multiple secured IP hops between the
Client's point of connection and the nearest Proxy/Server.
Mobile Ad-hoc NETwork (MANET)
a connected ANET region for which links often have undetermined
connectivity properties, lower layer security services cannot
always be assumed and multihop forwarding between Clients acting
as MANET routers may be necessary. AERO and the OMNI link model
naturally support MANET Internetworking [I-D.templin-manet-inet].
Internetwork (INET)
a connected network region with a coherent IP addressing plan that
provides transit forwarding services between (M)ANETs and AERO/
OMNI nodes that coordinate with the Mobility Service over
unprotected media. No physical and/or data link level security is
assumed, therefore security must be applied by the network and/or
higher layers. The global public Internet itself is an example.
End-user Network (EUN)
a simple or complex "downstream" network tethered to a Client as a
single logical unit that travels together. The EUN could be as
simple as a single link connecting a single end system, or as
complex as a large network with many links, routers, bridges and
end user devices. The EUN provides an "upstream" link for
arbitrarily many low-, medium- or high-end devices dependent on
the Client for their upstream connectivity, i.e., as Internet of
Things (IoT) entities. EUNs can also support a recursively-
descending chain of additional Clients such that the EUN of an
upstream Client appears as the (M)ANET of a downstream Client.
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*NET
a "wildcard" term used when a given specification applies equally
to all MANET/ANET/INET cases. From the Client's perspective, *NET
interfaces are "upstream" interfaces that connect the Client to
the Mobility Service, while EUN interfaces are "downstream"
interfaces that the Client uses to connect downstream *NETs which
may connect other Clients. Local communications between
correspondents within the same *NET can often be conducted based
on IPv6 ULAs [RFC4193] or MLAs [I-D.templin-6man-mla].
underlay network/interface
a *NET interface over which an OMNI interface is configured. The
network layer engages the OMNI interface as an ordinary network
interface, and the adaptation layer engages each underlay
interface as a link layer conduit. The underlay includes UDP/IP,
IP or NULL encapsulations for data units transferred between the
adaptation and link layers.
MANET Interface
a node's underlay interface to a local network with indeterminant
neighborhood properties over which multihop relaying may be
necessary. All MANET interfaces used by AERO/OMNI are IPv6
interfaces and therefore must configure a Maximum Transmission
Unit (MTU) no smaller than the IPv6 minimum MTU (1280 octets) even
if lower-layer fragmentation is needed.
OMNI link
the same as defined in [I-D.templin-6man-omni3]. The OMNI link
employs IPv6 encapsulation to traverse intermediate systems in a
spanning tree over underlay network segments the same as a bridged
campus LAN. AERO nodes on the OMNI link appear as single-hop
neighbors at the network layer even though they may be separated
by many underlay network hops; AERO nodes can employ Segment
Routing [RFC8402][RFC8754] to cause packets to visit selected
waypoints within the same OMNI link limited domain.
OMNI link segment
a Proxy/Server and all of its constituent Clients within any
attached *NETs is considered as a leaf OMNI link segment, with
each leaf interconnected via links and "bridge" nodes in
intermediate OMNI link segments. When the *NETs of multiple leaf
segments overlap (e.g., due to network mobility), they can combine
to form larger *NETs with no changes to Client-to-Proxy/Server
relationships. The OMNI link consists of the concatenation of all
OMNI link leaf and intermediate segments as a loop-free spanning
tree.
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OMNI interface
a node's virtual interface to an OMNI link, and configured over
one or more underlay interfaces. If there are multiple OMNI links
in an OMNI domain, a separate OMNI interface is configured for
each link. The OMNI interface configures a Maximum Transmission
Unit (MTU) and an Effective MTU to Receive (EMTU_R) the same as
any interface. The OMNI interface assigns an "external" LLA and
Ethernet link-layer address the same as for any IPv6 interface,
assigns a different "internal" LLA and link-layer address to
support a virtual internal router entity, and assigns an MLA for
adaptation layer addressing over underlay interfaces. Since OMNI
interface MLAs are managed for uniqueness and LLAs are used for
node-local operations only, OMNI interfaces assume Optimistic
Duplicate Address Detection (DAD) per [RFC4429].
OMNI Adaptation Layer (OAL)
an OMNI interface sublayer service that encapsulates original IP
packets admitted into the interface in an IPv6 header and/or
subjects them to fragmentation and reassembly. The OAL is also
responsible for generating MTU-related control messages as
necessary, and for providing addressing context for spanning
multiple segments of an extended OMNI link.
OMNI Option
a pseudo IPv6 ND option providing multilink parameters for the
OMNI interface. The OMNI option is appended to the end of a
control message during OAL encapsulation such that it appears
immediately following the final message option or composite packet
extension.
(network) partition
frequently, underlay networks such as large corporate enterprise
networks are sub-divided internally into separate isolated
partitions (a technique also known as "network segmentation").
Each partition is fully connected internally but disconnected from
other partitions, and there is no requirement that separate
partitions maintain consistent Internet Protocol and/or addressing
plans. (Each partition appears as a separate OMNI link segment as
discussed throughout this document.)
underlay network encapsulation
OMNI protocol encapsulation of OAL packets/fragments in an outer
header or headers to form carrier packets that can be routed
within the scope of the local *NET underlay network partition.
Common underlay network encapsulation combinations include UDP,
IP, Ethernet, etc. using a port/protocol/type number for OMNI.
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underlay-extended (UNX) address
an address that appears in encapsulations for an underlay
interface and also in control message OMNI options. UNX can be
either an IP address for IP encapsulations or an IEEE EUI address
[EUI] for direct data link encapsulation. (When UDP/IP
encapsulation is used, the UDP port number is regarded as an
extension of the IP UNX.)
original IP packet
a whole IP packet or fragment admitted into the OMNI interface by
the network layer prior to OAL encapsulation/fragmentation, or an
IP packet delivered to the network layer by the OMNI interface
following OAL reassembly/decapsulation.
OAL packet
an original IP packet encapsulated in an OAL IPv6 header with an
IPv6 Extended Fragment Header extension that includes an 8-octet
(64-bit) OAL Identification value. Each OAL packet is then
subject to fragmentation by the source and reassembly by the
destination.
OAL fragment
a portion of an OAL packet following fragmentation but prior to
underlay encapsulation, or following underlay decapsulation but
prior to OAL reassembly.
OAL atomic fragment
an OAL packet that can be forwarded without fragmentation, but
still includes an IPv6 Extended Fragment Header with an 8-octet
(64-bit) OAL Identification value and with Index and More
Fragments both set to 0. (Note that control message atomic
fragments also omit the Extended Fragment Header over secured
spanning tree links.)
carrier packet
an OAL packet or fragment submitted for underlay interface
encapsulation. OAL nodes exchange carrier packets over underlay
interfaces in a hop-by-hop fashion beginning with the OAL source,
then continuing over any OAL intermediate nodes and ending with
the OAL destination. Each intermediate hop removes the underlay
encapsulations of the previous hop and inserts underlay
encapsulations appropriate for the next hop. Carrier packets may
themselves be subject to fragmentation and reassembly in some IPv4
underlay networks at a layer below the OAL. Carrier packets sent
over unsecured paths use OMNI protocol underlay encapsulations,
while those sent over secured paths use security encapsulations
such as IPsec [RFC4301].
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OAL source
a node that configures an OMNI interface acts as an OAL source
when it encapsulates original IP packets to form OAL packets, then
performs OAL fragmentation and underlay encapsulation to create
carrier packets. Every OAL source is also an OAL end system.
OAL destination
a node that configures an OMNI interface acts as an OAL
destination when it decapsulates carrier packets, then performs
OAL reassembly/decapsulation to restore the original IP packet.
Every OAL destination is also an OAL end system.
OAL intermediate system
a node that configures an OMNI interface acts as an OAL
intermediate system when it decapsulates carrier packets received
from a first segment to obtain the OAL packet/fragment, then re-
encapsulates in new underlay headers and sends these new carrier
packets into the next segment. OAL intermediate systems decrement
the Hop Limit in OAL packets/fragments during forwarding, and
discard the OAL packet/fragment if the Hop Limit reaches 0. OAL
intermediate systems do not decrement the TTL/Hop Limit of the
original IP packet, which can only be updated by the network and
higher layers. OAL intermediate systems along the path explicitly
addressed by the OAL IPv6 Destination (e.g., Proxys, etc.) are
regarded as "endpoint" intermediate systems while those not
explicitly addressed (e.g., MANET routers, AERO Gateways, etc.)
are regarded as "transit" intermediate systems.
Mobility Service Prefix (MSP)
an aggregated IP GUA prefix (e.g., 2001:db8::/32,
2002:192.0.2.0::/40, etc.) assigned to the OMNI link and from
which more-specific Mobile Network Prefixes (MNPs) are delegated,
where IPv4 MSPs are represented as "6to4 prefixes" per [RFC3056].
OMNI link administrators typically obtain MSPs from an Internet
address registry, however private-use prefixes can alternatively
be used subject to certain limitations (see:
[I-D.templin-6man-omni3]). OMNI links that connect to the global
Internet advertise their MSPs to interdomain routing peers.
Mobile Network Prefix (MNP)
a longer IP GUA prefix derived from an MSP (e.g.,
2001:db8:1000:2000::/56, 2002:192.0.2.8::/48, etc.) and delegated
to an AERO Client.
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Foreign Network Prefix (FNP)
a global IP prefix not covered by a MSP and assigned to a link or
network outside of the AERO/OMNI domain. Relays advertise any of
their associated FNPs into the AERO/OMNI routing system and
forward packets between MNP mobile or fixed nodes on the OMNI link
and FNP correspondent nodes on other links.
Subnet Router Anycast (SRA) Address
An IPv6 address taken from an FNP/MNP in which the remainder of
the address beyond the final bit of the prefix is set to the value
"all-zeros". For example, the SRA for 2001:db8:1::/64 is simply
2001:db8:1:: (i.e., with the 64 least significant bits set to 0).
For IPv4, the IPv6 SRA corresponding to the IPv4 prefix
192.0.2.0/24 is 2002:192.0.2.0::/40 per [RFC3056].
Interface Identifier (IID)
the least significant 64 bits of an IPv6 address, as specified in
the IPv6 addressing architecture [RFC4291].
AERO node
a node that is connected to an OMNI link and participates in the
AERO internetworking and mobility service.
(AERO) (Proxy/)Client
an AERO node that configures an OMNI interface over one or more
underlay interfaces and requests MNP prefix delegations from AERO
Proxy/Servers. The Client assigns LLAs and an MLA to the OMNI
interface for use in IPv6 ND exchanges with other AERO nodes and
forwards original IP packets to correspondents according to OMNI
interface neighbor cache state. The Client coordinates with
Proxy/Servers and/or other Clients over upstream (M)ANET/INET
interfaces and may also provide Proxy services for other Clients
over downstream interfaces.
(AERO) Proxy/Server
an AERO node that provides a proxying service between AERO Clients
and external peers on its Client-facing (M)ANET interfaces (i.e.,
in the same fashion as for an enterprise network proxy) as well as
designated router services for coordination with correspondents on
its INET-facing interfaces. (Proxy/Servers in the open INET
instead configure only a single INET interface and no (M)ANET
interfaces.) The Proxy/Server configures an OMNI interface and
maintains BGP peerings with Gateways to provide a local anchor
point for its stable and/or mobile Clients.
(AERO) Relay
an AERO Proxy/Server that provides forwarding services between
nodes reached via the OMNI link and correspondents on foreign
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links/networks. AERO Relays maintain BGP peerings with Gateways
the same as Proxy/Servers. Relays also run a dynamic routing
protocol to discover any Foreign Network Prefix (FNP) routes in
service on other links/networks, advertise OMNI link MSP(s) to
other links/networks, and redistribute FNPs discovered on other
links/networks into the OMNI link BGP routing system. (Relays
that connect to major Internetworks such as the global IPv6 or
IPv4 Internets can also be configured to advertise "default"
routes into the OMNI link BGP routing system.)
(AERO) Gateway
a BGP hub autonomous system node that also provides OAL forwarding
services for nodes on an OMNI link. Gateways forward OAL packets/
fragments between OMNI link segments as OAL intermediate systems
while decrementing the OAL IPv6 header Hop Limit but without
decrementing the network layer IP TTL/Hop Limit. Gateways peer
with Proxy/Servers and other Gateways to form an IPv6-based OAL
spanning tree over all OMNI link segments and to discover the set
of all FNP/MNP prefixes in service. Gateways process OAL packets/
fragments received over the secured spanning tree that are
addressed to themselves, while forwarding all other OAL packets/
fragments to the next hop also via the secured spanning tree.
Gateways forward OAL packets/fragments received over the unsecured
spanning tree to the next hop either via the unsecured spanning
tree or via direct encapsulation if the next hop is on the same
OMNI link segment. It is important to note that all Gateways are
also Proxy/Servers, but only those Proxy/Servers configured as
intermediate nodes in the spanning tree are considered Gateways.
First-Hop Segment (FHS) Client
a Client that initiates communications with a target peer by
sending control messages to establish reverse-path multilink
forwarding state in OMNI link intermediate systems on the path to
the target. Note that in some arrangements the Client's (FHS)
Proxy/Server (and not the Client itself) initiates the exchange.
Last-Hop Segment (LHS) Client
a Client that responds to a communications request from a source
peer's initiation by returning a response message to establish
forward-path multilink forwarding state in OMNI link intermediate
systems on the path to the source. Note that in some arrangements
the Client's (LHS) Proxy/Server (and not the Client itself)
returns the response.
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First-Hop Segment (FHS) Proxy/Server
a Proxy/Server for an FHS Client's underlay interface that
forwards the Client's OAL packets into the segment management
topology. FHS Proxy/Servers also act as intermediate forwarding
systems to facilitate RS/RA exchanges between a Client and its MAP
Proxy/Server.
Last-Hop Segment (LHS) Proxy/Server
a Proxy/Server for an underlay interface of an LHS Client that
forwards OAL packets received from the segment management topology
to the Client over that interface.
Mobility Anchor Point (MAP) Proxy/Server
a Proxy/Server selected by a Client that injects the Client's MNP
into the BGP routing system and provides both forwarding and
mobility services for any *NET underlay interfaces that register
the MNP. Clients often select the first FHS Proxy/Server they
coordinate with to serve in the MAP role as all FHS Proxy/Servers
are equally capable candidates to serve as a MAP. The Client can
instead select any available Proxy/Server for the OMNI link as
there is no requirement that the MAP must also be one of the
Client's FHS Proxy/Servers. This flexible arrangement supports a
fully distributed mobility management service.
Segment Routing Topology (SRT)
a Multinet OMNI link forwarding region between FHS and LHS Proxy/
Servers. FHS/LHS Proxy/Servers and SRT Gateways span the OMNI
link on behalf of communicating peer nodes. The SRT maintains a
spanning tree established through BGP peerings between Gateways
and Proxy/Servers. Each SRT leaf segment includes Gateways in a
"hub" and Proxy/Servers in "spokes", while adjacent segments are
interconnected by Gateway-Gateway peerings. The BGP peerings are
configured over both secured and unsecured underlay network paths
such that a secured spanning tree is available for critical
control messages while other messages can use the unsecured
spanning tree.
Address Resolution Source (ARS)
the node nearest the original source that initiates OMNI link
address resolution. The ARS may be a Proxy/Server or Relay for
the source, or may be the source Client itself. The ARS is often
(but not always) also the same node that becomes the FHS source
during route optimization.
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Address Resolution Target (ART)
the node toward which address resolution is directed. The ART may
be a Relay or the target Client itself. The ART is often (but not
always) also the same node that becomes the LHS target during
route optimization.
Address Resolution Responder (ARR)
the node that responds to address resolution requests on behalf of
the ART. The ARR may be a Relay, the ART itself, or the ART's
current MAP Proxy/Server. Note that a MAP Proxy/Server can assume
the ARR role even if it is located on a different SRT segment than
the ART. The MAP Proxy/Server assumes the ARR role only when it
receives an RS message from the ART with the 'ARR' flag set (see:
[I-D.templin-6man-omni3]).
Potential Router List (PRL)
a geographically and/or topologically referenced list of addresses
of all Proxy/Servers within the same OMNI link segment. Each OMNI
link segment has its own PRL.
Distributed Mobility Management (DMM)
a BGP-based overlay routing service coordinated by Proxy/Servers
and Gateways that tracks all Proxy/Server-to-Client associations.
Mobility Service (MS)
the collective set of all Proxy/Servers, Gateways and Relays that
provide the AERO Service to Clients.
flow
a sequence of packets sent from a particular source to a
particular unicast, anycast, or multicast destination that a node
desires to label as a flow. The 3-tuple of (Source Address,
Destination Address, Flow Label) enables efficient IPv6 flow
classification. The IPv6 Flow Label Specification is observed per
[RFC6437] [RFC6438].
AERO Flow Information Base (AFIB)
A multilink forwarding table on each OAL source, destination and
intermediate system that includes AERO Flow Vectors (AFV) with
both next hop forwarding instructions and context for
reconstructing compressed headers for specific underlay interface
pairs used to transport flows from a source to a destination.
AERO Flow Vector (AFV)
An AFIB entry that includes soft state for each underlay interface
pairwise communication flow from source to destination. AFVs are
identified by an AFV Index (AFVI) paired with the previous hop
underlay address, with the pair established based on adaptation
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layer control messaging. The AFV also caches underlay interface
pairwise Identification sequence number parameters to support
carrier packet filtering.
AERO Flow Vector Index (AFVI)
A 2-octet or 4-octet integer value supplied by a previous hop OAL
node when it requests a next hop OAL node to create an AFV. (The
AFVI is always processed as a 4-octet value, but compressed
headers may omit the 2 most significant octets when they encode
the value 0.) The next hop OAL node caches the AFVI and underlay
address supplied by the previous hop as header compression/
decompression state for future OAL packets with compressed
headers. The previous hop OAL node must ensure that the AFVI
values it assigns to the next hop via a specific underlay
interface are distinct and reused only after their useful
lifetimes expire. The special value 0 means that no AFVI is
asserted.
3. Requirements
OMNI interfaces should limit the size of their control plane messages
to the adaptation layer path MTU which may be as small as the minimum
IPv6 link MTU minus encapsulation overhead. If there are sufficient
OMNI parameters and/or IP packet attachments that would exceed this
size, the OMNI interface forwards the information as multiple smaller
control messages and the recipient accepts the union of all
information received. This allows the messages to travel without
loss due to a size restriction over secured control plane paths that
include IPsec tunnels [RFC4301], secured direct point-to-point links
and/or unsecured paths that require an authentication signature.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119][RFC8174] when, and only when, they appear in all
capitals, as shown here.
4. Automatic Extended Route Optimization (AERO)
The following sections specify the operation of IP over OMNI links
using the AERO service:
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4.1. AERO Node Types
AERO (Proxy/)Clients can be deployed as fixed infrastructure nodes
close to end systems, or as Mobile Nodes (MNs) that can change their
network attachment points dynamically. AERO Clients configure OMNI
interfaces over underlay interfaces with addresses that may change
due to mobility. AERO Clients that obtain MNPs register them with
the AERO service, and distribute the MNPs to EUNs (which may connect
other Clients). AERO Clients can also provide Proxy services for
other Clients on downstream-attached networks.
AERO Gateways, Proxy/Servers and Relays are infrastructure elements
in *NET boundary (or standalone INET) deployments and hence have INET
addresses that rarely (if ever) change. Together, they provide
access to the AERO service OMNI link virtual overlay for connecting
AERO Clients. AERO Gateways (together with Proxy/Servers and Relays)
provide the secured backbone supporting infrastructure for an OMNI
link Segment Routing Topology (SRT) spanning tree.
AERO Gateways are Proxy/Servers deployed as OMNI link intermediate
systems that forward packets both within the same SRT segment and
between disjoint SRT segments based on an IPv6 encapsulation mid-
layer known as the OMNI Adaptation Layer (OAL). The OMNI interface
and OAL provide an adaptation layer forwarding service that the
network layer perceives as L2 bridging, since the inner IP TTL/Hop
Limit is not decremented. Each Gateway peers with Proxy/Servers,
Relays and other Gateways in a dynamic routing protocol instance as a
Distributed Mobility Management (DMM) service for the list of active
MNPs (see: Section 4.2.3). Gateways assign one or more Mobility
Service Prefixes (MSPs) to the OMNI link and configure IPsec tunnels
with Proxy/Servers, Relays and other Gateways; they further maintain
forwarding table entries for each FNP/MNP prefix in service on the
OMNI link.
AERO Proxy/Servers distributed across one or more SRT segments
provide default forwarding and mobility/multilink services for AERO
Client mobile nodes. Each Proxy/Server acts as either an OMNI link
intermediate system or end system according to the service model
selected by the Client. Each Proxy/Server also peers with Gateways
in an adaptation layer dynamic routing protocol instance to advertise
its list of associated MNPs (see: Section 4.2.3). MAP Proxy/Servers
provide prefix delegation services and track the mobility/multilink
profiles of each of their associated Clients, where each delegated
prefix becomes an MNP taken from an MSP. Proxy/Servers at *NET
boundaries provide a primary forwarding service for (M)ANET Client
communications with peers in external INETs. Proxy/Servers in open
INETs provide an authentication service for control messages but
should be considered as a less preferred data plane forwarding
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service when a Client cannot forward directly to an INET peer.
Source Clients securely coordinate with target Clients by sending
control messages via a First-Hop Segment (FHS) Proxy/Server which
forwards them over the SRT spanning tree to a Last-Hop Segment (LHS)
Proxy/Server which finally forwards them to the target.
AERO Relays are Proxy/Servers that provide forwarding services to
exchange original IP packets between the OMNI link and fixed or
mobile nodes on other links/networks. Relays run a dynamic routing
protocol to discover any FNP prefixes in service on foreign links/
networks, and Relays that connect to larger Internetworks (such as
the Internet) may originate default routes. The Relay redistributes
OMNI link MSP(s) into other links/networks, and redistributes FNPs
via OMNI link Gateway BGP peerings.
4.2. The AERO Service over OMNI Links
4.2.1. AERO/OMNI Reference Model
Figure 1 presents the basic OMNI link reference model:
+-----------------+
| AERO Gateway G1 |
| Nbr: S1, S2, P1 |
|(X1->S1; X2->S2) |
| MSP M1 |
+--------+--------+
+--------------+ | +--------------+
| AERO P/S S1 | | | AERO P/S S2 |
| Nbr: C1, G1 | | | Nbr: C2, G1 |
| default->G1 | | | default->G1 |
| X1->C1 | | | X2->C2 |
+-------+------+ | +------+-------+
| OMNI link | |
X===+===+==================+===================+===+===X
| |
+-----+--------+ +--------+-----+
|AERO Client C1| |AERO Client C2|
| Nbr: S1 | | Nbr: S2 |
| default->S1 | | default->S2 |
| MNP X1 | | MNP X2 |
+------+-------+ +-----+--------+
| |
.-. .-.
,-( _)-. +-------+ +-------+ ,-( _)-.
.-(_ IP )-. |IP end | |IP end | .-(_ IP )-.
(__ EUN )--|system | |system |--(__ EUN )
`-(______)-' +-------+ +-------+ `-(______)-'
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Figure 1: AERO/OMNI Reference Model
In this model:
* the OMNI link is an overlay network service configured over one or
more underlay SRT segments which may be managed by diverse
administrative domains using incompatible protocols and/or
addressing plans.
* AERO Gateway G1 aggregates Mobility Service Prefix (MSP) M1,
discovers Mobile Network Prefixes (MNPs) X* and advertises the MSP
via BGP peerings over secured tunnels to other Gateways in the SRT
(not shown). Together, the set of all Gateways provide the
backbone for an SRT spanning tree for the OMNI link.
* AERO Proxy/Servers S1 and S2 configure secured tunnels with
Gateway G1 and also provide mobility, multilink, multicast and
default router services for the MNPs of their associated Clients
C1 and C2. (Proxy/Servers that act as Relays can also advertise
FNP routes for non-mobile correspondent nodes the same as for MNP
Clients.)
* AERO Clients C1 and C2 associate with Proxy/Servers S1 and S2,
respectively. They receive MNP delegations X1 and X2, and also
act as default routers for their associated physical or internal
virtual EUNs. (While not shown, AERO Clients can also be
recursively nested in an arbitrarily-deep chain of (Proxy/)Clients
between a Proxy/Server and the ultimate IP end systems.)
* IP end systems attach to the EUNs served by Clients C1 and C2,
respectively. (Although not depicted here, there may be multiple
Proxy/Client intermediate systems between Clients C1 and C2 and
the ultimate IP end systems.)
An OMNI link configured over a single underlay network appears as a
single unified link with a consistent addressing plan; all nodes on
the link can exchange carrier packets via simple underlay
encapsulation (i.e., following any necessary NAT traversal) since the
underlay is connected. In common practice, however, OMNI links are
often configured over an SRT spanning tree that bridges multiple
distinct underlay network segments managed under different
administrative authorities (e.g., as for worldwide aviation service
providers such as ARINC, SITA, Inmarsat, etc.). Individual underlay
networks may also be partitioned internally, in which case each
internal partition appears as a separate segment.
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The addressing plan of each SRT segment is consistent internally but
will often bear no relation to the addressing plans of other
segments. Each segment is also likely to be separated from others by
network security devices (e.g., firewalls, proxys, packet filtering
gateways, etc.), and disjoint segments often have no common physical
link connections. Therefore, nodes can only be assured of exchanging
carrier packets directly with correspondents in the same segment, and
not with those in other segments. The only means for joining the
segments therefore is through inter-domain peerings between AERO
Gateways.
The OMNI link spans multiple SRT segments using the OAL to provide
the network layer with a virtual abstraction similar to a bridged
campus LAN. The OAL is an OMNI interface sublayer that inserts a
mid-layer IPv6 encapsulation header for inter-segment forwarding
(i.e., bridging) without decrementing the network layer TTL/Hop Limit
of the original IP packet. An example OMNI link SRT is shown in
Figure 2:
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. .
. .
. .-(::::::::) .-(::::::::) .-(::::::::) .
. .-(::::::::::::)-. +-+ .-(::::::::::::)-. +-+ .-(::::::::::::)-. .
. (:::: FHS :::)--|G|--(::: Intermediate ::)--|G|--(:::: LHS :::) .
. `-(::::::::::::)-' +-+ `-(::Segments::)-' +-+ `-(::::::::::::)-' .
. `-(::::::)-' `-(::::::)-' `-(::::::)-' .
. | | .
. +---+ +---+ .
. |P/S| |P/S| .
. +---+ +---+ .
. | | .
. .-(::::::::) .-(::::::::) .
. .-(: First Hop :)-. +-------+ +-------+ .-(: Last Hop :)-. .
. (:::: Access ::::)--| Source| | Target|--(:::: Access ::::) .
. `-(:: Network ::)-' | Client| | Client| (:: Network ::)-' .
. `-(::::::)-' +-------+ +-------+ `-(::::::)-' .
. .
. .
. <-- Segment Routing Topology (SRT) Spanned by OMNI Link --> .
. .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 2: OMNI Link Segment Routing Topology (SRT)
In the Segment Routing Topology, a source Client connects via a first
hop access network served by a First Hop Segment (FHS) Proxy/Server.
The FHS Proxy/Server then forwards to an FHS Gateway which connects
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to an arbitrarily complex set of Intermediate Segments. Adjacent
intermediate Segments are joined by intermediate Gateways (not shown)
that serve as adaptation layer IPv6 routers, with the final segment
connected by a Last Hop Segment (LHS) Gateway. The LHS Gateway then
forwards to an LHS Proxy/Server which in turn connects to the last
hop access network where the target Client resides.
Gateway, Proxy/Server and Relay OMNI interfaces are configured over
both secured tunnels and open INET underlay interfaces within their
respective SRT segments. Within each segment, Gateways configure
"hub-and-spokes" BGP peerings with Proxy/Servers and Relays as
"spokes". Adjacent SRT segments are joined by Gateway-to-Gateway
peerings to collectively form a spanning tree over the entire SRT.
The "secured spanning tree" supports authentication and integrity for
critical control plane messages (and any trailing data plane message
extensions). The "unsecured spanning tree" conveys ordinary carrier
packets without security codes and that must be examined by
destinations according to data origin authentication procedures.
AERO nodes can employ route optimization to cause carrier packets to
take more direct paths between OMNI link neighbors without having to
follow strict spanning tree paths.
The network of networks concept emerged from the earliest days of
Internetworking [CERF1][KAHN][POUZIN]. The concept has carried
forward to the present day where the Internet has become successful
beyond measure. The AERO Multinet service concatenates SRT segments
through Gateway-to-Gateway peerings as first suggested in
"Interconnection of Packet switching Networks" [POUZIN] and later
formalized in the "Catenet Model for Internetworking (IEN48)"
[CERF2]. The catenet model in particular suggests an interconnection
of independent and diverse packet switching network "segments" to
form a much larger Internetwork supporting end-to-end services.
The catenet vision faded into obscurity as the Internet evolved in
the decades that followed, and the adaptation layer was omitted from
the architecture. As a result, the Internet has flourished as a
monolithic public routing and addressing service interconnecting
private domains leading to the rise of the middle (including NATs)
and a diminished role for end-to-end [RFC3724]. The adaptation layer
manifested by AERO and OMNI now promises to restore the best aspects
of end-to-end through incremental deployment of catenet constructs in
the modern Internet.
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4.2.2. AERO Addressing
AERO nodes on OMNI links assign an external Link-Local Address (LLA)
and link-layer address on the OMNI interface as required by
[RFC4861]. AERO nodes also assign different internal LLA and link-
layer addresses to support the operation of an adaptation layer
internal virtual router entity.
AERO nodes assign a Multilink Local Address (MLA) to the OMNI
interface per [I-D.templin-6man-mla]. The node assigns an MLA to an
OMNI interface the same as suggested for "sites" in the IPv6 scoped
addressing architecture [RFC4007], i.e., as a single adaptation layer
address assigned to a virtual interface configured over potentially
multiple underlying interfaces.
MLAs are considered as adaptation layer addresses in the architecture
and can appear as OAL encapsulation addresses, but nodes may also use
them as the Source and Destination Addresses of original IP packets
exchanged between peers within the same OMNI link segment. Each
original IP packet with MLA addresses is subject to OAL encapsulation
with an IPv6 header that also uses MLA addresses.
AERO Clients receive Mobile Network Prefix (MNP) delegations during
Proxy/Server RS/RA exchanges and assign the MNPs to EUN interfaces.
AERO MSPs, MNPs and Foreign Network Prefixes (FNPs) are typically
based on GUAs, but in some cases may be based on IPv4 private
addresses [RFC1918] or IPv6 ULA-C's [RFC4193].
AERO address selection rules are conducted per [RFC6724] as updated
by [I-D.ietf-6man-rfc6724-update].
See [I-D.templin-6man-omni3] for a full discussion of the various
unicast, anycast and multicast addresses used by AERO nodes on OMNI
links.
4.2.3. AERO Overlay Routing System
The AERO routing system comprises a private Border Gateway Protocol
(BGP) [RFC4271] service coordinated between Gateways as interior
nodes and Proxy/Servers and Relays as leaf nodes of a spanning tree.
The service supports OAL packet/fragment forwarding at a layer below
IP and does not interact with the public Internet BGP routing system,
but supports redistribution of information for other networks
connected by Relays.
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In a reference deployment, each Proxy/Server is configured as an
Autonomous System Border Router (ASBR) for a stub Autonomous System
(AS) using a 32-bit AS Number (ASN) [RFC4271] that is unique within
the BGP instance, and each Proxy/Server further uses eBGP to peer
with one or more Gateways but does not peer with other Proxy/Servers.
Each SRT segment in the OMNI link must include one or more Gateways
in a "hub" AS, which peer with the Proxy/Servers within that segment
as "spoke" ASes. All Gateways within the same segment are members of
the same hub AS, and use iBGP to maintain a consistent view of all
active routes currently in service. The Gateways of different
segments peer with one another using eBGP.
Gateways maintain forwarding table entries for the set of all MLAs
and FNP/MNP routes that are currently active for the OMNI link;
Gateways also maintain black-hole routes for the OMNI link MSPs so
that OAL packets/fragments destined to non-existent more-specific
routes are flushed from the routing system. In this way, Proxy/
Servers and Relays have only partial topology knowledge (i.e., they
only maintain routing information for their directly associated
Clients and foreign links) and they forward all other OAL packets/
fragments to Gateways which have full topology knowledge.
MLAs and FNP/MNP routes are dynamically advertised in the AERO
routing system by Proxy/Servers and Relays that provide anchor points
for their corresponding prefixes. For example, if three Proxy/
Servers ('D', 'E' and 'F') service the MNPs 2001:db8:1000:1::64/,
2001:db8:1000:2::/64 and 2001:db8:1000:2::/48 then the routing system
would include:
D: 2001:db8:1000:1::/64
E: 2001:db8:1000:2::/64
F: 2001:db8:1000:3::/64
A full discussion of the BGP-based routing system used by AERO is
found in [I-D.ietf-rtgwg-atn-bgp].
4.2.4. Segment Routing Topologies (SRTs)
The distinct GUA prefixes in an OMNI link domain identify distinct
Segment Routing Topologies (SRTs). Each SRT is a mutually-exclusive
OMNI link overlay instance using a distinct set of GUAs, and emulates
a bridged campus LAN service for the OMNI link. In some cases (e.g.,
when redundant topologies are needed for fault tolerance and
reliability) it may be beneficial to deploy multiple SRTs that act as
independent overlay instances. A communication failure in one
instance therefore will not affect communications in other instances.
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Each SRT is identified by a distinct MSP prefix and assigns an IPv6
SRA address used for OMNI interface determination in Safety-Based
Multilink (SBM) as discussed in [I-D.templin-6man-omni3]. Each OMNI
interface further applies Performance-Based Multilink (PBM)
internally.
The Gateways and Proxy/Servers of each independent SRT engage in BGP
peerings to form a spanning tree with the Gateways in non-leaf nodes
and the Proxy/Servers in leaf nodes. The spanning tree is configured
over both secured and unsecured underlay network paths. The secured
spanning tree is used to convey secured control messages (and
sometimes data message extensions) between Proxy/Servers and
Gateways, while the unsecured spanning tree forwards bulk data
messages and/or unsecured control messages.
Each SRT segment is identified by a unique MSP prefix used by all
Proxy/Servers and Gateways in the segment. Each AERO node must
therefore discover an SRT prefix that correspondents can use to
determine the correct segment, and must publish the SRT prefix in
control messages.
Note: The distinct MSP prefixes in an OMNI link domain can be carried
either in a common BGP routing protocol instance for all OMNI links
or in distinct BGP routing protocol instances for different OMNI
links. In some SBM environments, such separation may be necessary to
ensure that distinct OMNI links do not include any common
infrastructure elements as single points of failure. In other
environments, carrying the MSPs of multiple OMNI links within a
common routing system may be acceptable.
4.3. OMNI Interface Characteristics
OMNI interfaces are virtual interfaces configured over one or more
underlay interfaces classified as follows:
* (M)ANET interfaces connect to a protected and secured ANET or an
open MANET that connects to an INET via Proxy/Servers. The
(M)ANET interface may be either on the same L2 link segment as a
Proxy/Server, or separated from a Proxy/Server by multiple IP
hops. (Note that NATs may appear internally within a (M)ANET and
may require NAT traversal on the path to the Proxy/Server the same
as for the INET case.) MANETs are special cases of ANETs in which
adaptation layer multihop forwarding may be necessary, and
protected secured underlay links cannot always be assumed.
* INET interfaces connect to an INET either natively or through one
or several IPv4 Network Address Translators (NATs). Native INET
interfaces have global IP addresses that are reachable from
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correspondent on the same INET. NATed INET interfaces typically
have private IP addresses and connect to a private network behind
one or more NATs with the outermost NAT providing INET access.
* EUN interfaces connect a Client's downstream-attached networks,
where the Client provides forwarding services for EUN end system
communications to remote peers. An EUN can be as simple as a
small IoT sub-network that travels with a mobile Client to as
complex as a large private enterprise network that the Client
connects to a larger ANET or INET.
* VPN interfaces use security encapsulations (e.g. IPsec tunnels)
over underlay networks to connect Clients, Proxy/Servers and/or
Gateways. VPN interfaces provide security services at lower
layers of the architecture the same as for Direct point-to-point
interfaces.
* Direct point-to-point interfaces securely connect Clients, Proxy/
Servers and/or Gateways over physical or virtual media that does
not transit any open Internetwork paths. Examples include a line-
of-sight link between a remote pilot and an unmanned aircraft, a
fiberoptic link between Gateways, etc.
OMNI interfaces use OAL encapsulation and fragmentation as discussed
in Section 4.6. OMNI interfaces use underlay encapsulation (see:
Section 4.6) to exchange carrier packets with OMNI link neighbors
over INET interfaces and IPsec tunnels as well as over ANET
interfaces for which the Client and neighbor may be multiple IP hops
away. OMNI interfaces use link layer encapsulation only (i.e., and
no other underlay encapsulations) over Direct underlay interfaces or
(M)ANET interfaces when the Client and neighbor are known to be on
the same underlay link.
OMNI interfaces maintain an adaptation layer view of the neighbor
cache for tracking per-neighbor state. IP nodes that configure OMNI
interfaces use IPv6 ND messages to manage both the network and
adaptation layer views of the neighbor cache. The adaptation layer
further uses MP multilink forwarding control messages which consist
of an ordinary packet for a flow with an OMNI option trailer. OMNI
neighbors invoke per-flow OAL Identification window synchronization
in their control message exchanges to enable Source Address
verification, header compression and robust fragmentation/reassembly.
OMNI interfaces include OMNI options formatted as specified in
[I-D.templin-6man-omni3] in the control messages they forward. The
OMNI option includes parameters for coordinating the OMNI interface's
underlay interfaces.
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A Client's OMNI interface may be configured over multiple *NET
underlay interfaces. For example, common mobile handheld devices
have both wireless local area network ("WLAN") and cellular wireless
links. These links are often used "one at a time" with low-cost WLAN
preferred and highly-available cellular wireless as a standby, but a
simultaneous-use capability could provide benefits. In a more
complex example, aircraft frequently have many wireless data link
types (e.g. satellite-based, cellular, terrestrial, air-to-air
directional, etc.) with diverse performance and cost properties.
If a Client's multiple *NET underlay interfaces are used "one at a
time" (i.e., all other interfaces are in standby mode while one
interface is active), then successive control messages all include
OMNI option Interface Attributes, Traffic Selector and/or Neighbor
Synchronization sub-options with the same underlay interface ifIndex.
In that case, the Client would appear to have a single underlay
interface but with a dynamically changing underlay address.
If the Client has multiple active *NET underlay interfaces, then from
the perspective of IPv6 ND it would appear to have multiple underlay
addresses. In that case, control message OMNI options MAY include
multiple Interface Attribute sub-options; each with a different
underlay interface ifIndex.
Proxy/Servers on the open Internet include only a single INET
underlay interface. INET Clients therefore discover only the UNX
information for the Proxy/Server's INET interface. Proxy/Servers on
a (M)ANET/INET boundary include both (M)ANET and INET underlay
interfaces. (M)ANET Clients therefore must discover both the (M)ANET
and INET UNX information for their Proxy/Servers.
Gateway and Proxy/Server OMNI interface connections to the SRT are
configured over both secured IPsec tunnels for carrying IPv6 ND and
BGP protocol control plane messages and open INET paths for carrying
unsecured data plane messages. The OMNI interface configures an MLA
and acts as an OAL source to encapsulate original IP packets, then
fragments the resulting OAL packets, performs underlay encapsulation
and sends the resulting carrier packets over the secured or unsecured
underlay paths. Note that Gateway and Proxy/Server end-to-end
transport protocol sessions used by the BGP run directly over the
OMNI interface and use MLA IPv6 Source and Destination Addresses.
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4.4. OMNI Interface Initialization
AERO Proxy/Servers and Clients configure OMNI interfaces as their
point of attachment to the OMNI link. AERO nodes assign the MSPs for
the link to their OMNI interfaces (i.e., as a "route-to-interface")
to ensure that original IP packets with Destination Addresses covered
by an MNP not explicitly associated with another interface are
directed to an OMNI interface where address resolution is applied.
OMNI interface initialization procedures for Gateways, Proxy/Servers
and Clients are discussed in the following sections.
4.4.1. AERO Gateway Behavior
AERO Gateways configure an OMNI interface and assign an MLA.
Gateways configure underlay interface secured tunnels with Proxy/
Servers in the same SRT segment and other Gateways in the same (or an
adjacent) SRT segment. Gateways then engage in an adaptation layer
BGP routing protocol session with neighbors over the secured spanning
tree (see: Section 4.2.3).
4.4.2. AERO Proxy/Server and Relay Behavior
When a Proxy/Server enables an OMNI interface, it assigns both an LLA
and MLA. The Proxy/Server also configures secured underlay interface
tunnels and engages in adaptation layer BGP routing protocol sessions
over the OMNI interface with one or more neighboring Gateways.
The OMNI interface provides a single interface abstraction to the
network layer, but internally serves as an NBMA nexus for exchanging
carrier packets with other OMNI nodes over underlay interfaces and/or
secured tunnels. The Proxy/Server further configures a service to
facilitate control message exchanges with AERO Clients and manages
per-Client Neighbor Cache Entries (NCEs) and IP forwarding table
entries based on control message exchanges.
Relays are simply Proxy/Servers that run a dynamic routing protocol
to redistribute routes between the OMNI interface and foreign
networks/links (see: Section 4.2.3). The Relay provisions MNPs and
advertises the MSP(s) for the OMNI link over its foreign network
interface attachments. The Relay further provides an OMNI link
attachment point for FNP-based topologies.
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4.4.3. AERO Client Behavior
When a Client enables an OMNI interface, it assigns different
administratively assigned internal and external LLAs and link-layer
addresses as well as a globally unique MLA to the OMNI interface.
The adaptation layer within the interface then issues an internally-
generated RA message to the network layer to establish itself as a
(virtual) default router for the OMNI link. The network layer then
issues a DHCPv6 Prefix Delegation (PD) request per [RFC9762]. When
it receives the PD request (or after a brief timeout), the adaptation
layer then sends OMNI-encapsulated RS messages to FHS Proxy/Servers
which optionally coordinate with a MAP Proxy/Server that delegates
one or more MNPs. The MAP/FHS Proxy/Servers then return an RA
message to the Client which may pass through one or more NATs in the
path.
When the Client sends initial RS messages, it will discover MNPs in
the corresponding RAs that it receives from FHS Proxy/Servers and can
then associate them with the OMNI interface. If the Client is
operating outside the context of AERO infrastructure, however, it may
continue using MLAs over its underlay or OMNI interfaces for peer-to-
peer communications within the local *NET.
4.5. OMNI Interface Neighbor Cache Maintenance
Each Client and Proxy/Server OMNI interface maintains a network layer
conceptual Neighbor and Destination Cache per [RFC1256][RFC4861] the
same as for any IP interface. The OMNI interface network layer
neighbor cache (NLNC) is maintained through static and/or dynamic
neighbor cache entry (NLNCE) configurations. The IP layer initiates
and terminates IP ND messaging exchanges to manage the network layer
view of the neighbor cache.
Each OMNI interface also maintains an internal adaptation layer view
of the neighbor cache (ALNC) that includes an entry (ALNCE) for each
of its active OAL neighbors. ALNCE state is managed according to
neighbor cache entry states per Section 7.3.2 of [RFC4861] the same
as the NLNC. The adaptation layer indexes the ALNC by the neighbor's
MLA and includes routing information for any of the neighbor's FNPs/
MNPs. Control messages that update the ALNC include an OMNI option
with zero or more sub-options.
Each OMNI interface ALNCE is indexed by the IPv6 MLA of a neighbor
found in an ND message and determines the context for Identification
verification. Clients and Proxy/Servers maintain NCEs through
dynamic RS/RA message exchanges, and also maintain NCEs for any
active correspondent peers through dynamic IPv6 NS/NA message
exchanges.
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Clients establish NCEs and establish adaptation layer service
profiles for their associated FHS and MAP Proxy/Servers through the
exchange of RS/RA messages as specified in [I-D.templin-6man-omni3].
When a Client and Proxy/Server establish NCEs, they set a
ReachableTime timer to REACHABLE_TIME seconds.
Both the Client and its MAP Proxy/Server have full knowledge of the
Client's current underlay Interface Attributes and Traffic Selectors,
while FHS Proxy/Servers acting in "proxy" mode have knowledge of only
the individual Client underlay interfaces they service.
When an Address Resolution Source (ARS) sends an NS(AR) message
toward an Address Resolution Target (ART) Client/Relay, the OMNI link
routing system directs the NS(AR) to a MAP Proxy/Server for the ART.
The MAP then either acts as an Address Resolution Responder (ARR) on
behalf of the ART or forwards the NS(AR) to the ART which acts as an
ARR on its own behalf. The ARR returns an NA(AR) response to the
ARS, which creates or updates NCE state for the ART while caching
network layer and underlay addressing information. The ARS then
(re)sets ReachableTime for the NCE to REACHABLE_TIME seconds and
performs multilink forwarding ND message exchanges over specific
underlay interface pairs to determine paths for sending carrier
packets directly to the ART. The ARS otherwise decrements
ReachableTime while no further solicited ND messages arrive.
Proxy/Servers add an additional state DEPARTED to the list of NCE
states found in Section 7.3.2 of [RFC4861]. When a Client terminates
its association, the Proxy/Server OMNI interface sets a DepartTime
variable for the NCE to DEPART_TIME seconds. DepartTime is
decremented unless a new control message causes the state to return
to REACHABLE. While a NCE is in the DEPARTED state, the Proxy/Server
forwards OAL packets/fragments destined to the target Client to the
Client's new FHS/MAP Proxy/Server instead.
It is RECOMMENDED that REACHABLE_TIME be set to the default constant
value 30 seconds as specified in [RFC4861]. It is RECOMMENDED that
DEPART_TIME be set to the default constant value 10 seconds to accept
any carrier packets that may be in flight. When ReachableTime or
DepartTime decrement to 0, the NCE is deleted.
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AERO nodes also use the value MAX_UNICAST_SOLICIT to limit the number
of NS(NUD) messages sent when a correspondent may have gone
unreachable, the value MAX_RTR_SOLICITATIONS to limit the number of
RS messages sent without receiving an RA and the value
MAX_NEIGHBOR_ADVERTISEMENT to limit the number of solicited IPv6 ND
advertisements that can be sent based on a single event. It is
RECOMMENDED that MAX_UNICAST_SOLICIT, MAX_RTR_SOLICITATIONS and
MAX_NEIGHBOR_ADVERTISEMENT be set to 3 the same as specified in
[RFC4861].
Different values for the above constants MAY be administratively set;
however, if different values are chosen, all nodes on the link MUST
consistently configure the same values.
4.5.1. AERO/OMNI Control Plane Messages
OMNI interfaces use IPv6 ND messages as the secured control plane
messaging service for all adaptation layer neighbor coordination
exchanges. IPv6 ND messages sent over OMNI interfaces include or
omit the Source/Target Link Layer Address Option (S/TLLAO) as
discussed in [I-D.templin-6man-omni3]. OMNI interfaces forward IPv6
ND messages to and from the IP layer the same as for standard IPv6
ND, but also append/remove a trailing OMNI pseudo-option during
encapsulation/decapsulation [I-D.templin-6man-omni3].
For each IPv6 ND message, the OMNI interface includes a trailing OMNI
option following any other ND message options then completely
populates all sub-option information. If the OMNI interface includes
an authentication sub-option, it calculates and includes a digital
signature per the OMNI specification. OMNI interfaces verify
integrity and authenticity of each message received, and process the
message further only following successful verification.
OMNI options include per-neighbor information that provides multilink
forwarding, address resolution and traffic selector information for
the neighbor's underlay interfaces. This information is stored in
both the neighbor cache and AERO Flow Information Base (AFIB) as
basis for the forwarding algorithm specified in Section 4.10. The
information is cumulative and reflects the union of the OMNI
information from the most recent IPv6 ND messages received from the
neighbor.
AERO/OMNI Clients send RS messages to cause Proxy/Servers to respond
with RA messages that include autoconfiguration and addressing
parameters as specified in [I-D.templin-6man-omni3].
AERO nodes use NS/NA messages as follows:
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* NS/NA(AR) messages are used for address resolution. When an ARS
prepares an NS(AR) it sets the Source Address to the IPv6 MLA
assigned to the OMNI interface. The ARS also sets the Target
Address to the IP Destination Address of the invoking packet and
sets the Destination Address to the solicited-node multicast
address corresponding to the (unicast) Target Address. After the
ARS sends the NS(AR), an ARR with addressing information for the
ART returns a unicast NA(AR) that contains current, consistent and
authentic Target Address resolution information. The ARR sets the
NA(AR) Source Address to an IPv6 MLA assigned to the ART's OMNI
interface, sets the Destination Address to the Source Address of
the NS(AR) and sets the Target Address to the Target Address of
the NS(AR). NS/NA(AR) messages must be secured.
* Other NS/NA message exchanges are used to determine target
reachability (NS/NA(NUD)). These messages include the same
addresses as for NS/NA(AR) with the exception that the source sets
the NS(NUD) Destination and Target Address to the same unicast
address. The target then returns a responsive NA(NUD). NS/
NA(NUD) messages used to establish or update NCE state must be
secured.
* Unsolicited NA messages (uNAs) are used to update a neighbor's
cache when an underlay interface address changes due to a mobility
event. Nodes also use uNAs during Route Optimization.
* NS/NA(DAD) messages are not used in AERO, since Duplicate Address
Detection is not required on OMNI links. When the network layer
issues an NS(DAD) message over an OMNI interface, the interface
simply discards the message.
AERO also introduces a control message type termed "Multilink Pilot
(MP)" which consists of an ordinary IP packet with an OMNI option
trailer and used to establish multilink forwarding state. The OAL
source may send MPs as initial messages of a flow until header
compression can be applied for further messages of the flow.
AERO control messages sent on OMNI links that must be examined by
transit OAL intermediate systems on the path require a special
codepoint for control message recognition. The OAL source therefore
sets the DSCP field in the IPv6 OAL encapsulation header of such
messages to the special value '111111' (see:
[I-D.templin-6man-omni3]) and includes an OMNI option trailer with
control information. The control planes of transit OAL intermediate
systems can then intercept and process these messages before
forwarding them to the next OAL hop.
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AERO control messages also include an SRH extension to the OAL IPv6
header as discussed in [I-D.templin-6man-omni3]. The SRH includes
any FHS intermediate system MLAs as non-ultimate Segment List
entries, the MLA of the LHS Proxy/Server as the penultimate entry and
the MLA of the target LHS Client as the ultimate entry.
4.5.2. OMNI Neighbor Window Synchronization
In secured environments (e.g., between secured spanning tree
neighbors, between neighbors on the same secured ANET, etc.), OMNI
interface neighbors can exchange AERO control messages without
including Identification values. In environments where spoofing is
considered a threat, OMNI interface neighbors instead invoke
Identification window synchronization by including OMNI Neighbor
Synchronization sub-options in control message exchanges to maintain
send/receive window state in their respective neighbor caches as well
as in AFIB entries of all OAL intermediate nodes in the forward and
reverse paths.
In common arrangements, OAL Identification window synchronization is
necessary for Client to Client, Client to Proxy/Server or Proxy/
Server to Proxy/Server message exchanges conducted over unsecured
Internetwork paths. Conversely, Proxy/Server to Proxy/Server, Proxy/
Server to Gateway and Gateway to Gateway message exchanges carried
over the secured spanning tree do not require window synchronization.
OAL end system and intermediate nodes verify Identification values of
OAL packets that traverse the unsecured spanning tree according to
their populated AFIB state. This allows each OAL node to exclude
spurious packets injected into the OMNI link from an off-path
adversary.
4.6. OMNI Interface Encapsulation and Fragmentation
When the network layer forwards an original IP packet into an OMNI
interface, the interface locates a NLNCE corresponding to the
destination (which may only match "default"). The OMNI interface
then invokes the OAL as discussed in [I-D.templin-6man-omni3] which
removes the virtual Ethernet header and encapsulates the packet in an
IPv6 header to form an OAL packet according to ALNCE information.
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Following encapsulation, the OAL source then fragments the OAL packet
while including an identical Identification value for each fragment
that must be within the window for the flow over the interface pair
selected for the neighbor. The OAL source includes any necessary OAL
IPv6 extension headers including an identical SRH with each fragment.
The OAL source can instead invoke OAL header compression by replacing
the full OAL IPv6 header, SRH and Extended Fragment Header with an
OAL Compressed Header (OCH) that includes an AERO Flow Vector Index
(AFVI) (see: [I-D.templin-6man-omni3]).
For messages that will traverse unsecured paths, the OAL source
finally performs underlay encapsulation on each resulting OAL
fragment to form a carrier packet, with Source Address set to its own
address (e.g., 192.0.2.100) and Destination Address set to the
address of the next hop OAL intermediate system or destination (e.g.,
192.0.2.1). The carrier packet encapsulation format in the above
example is shown in Figure 3:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Underlay Headers |
~ src = 192.0.2.100 ~
| dst = 192.0.2.1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~Underlay IPv6 Extension Headers~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OAL IPv6 Header |
~ Source Address (1) ~
| Destination Address (2) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ OAL IPv6 Extension Headers ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Original IP Header |
~ (first-fragment only) ~
~ Source Address (3) ~
| Destination Address (4) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ ~
~ Original Packet Body/Fragment ~
~ ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Carrier Packet Format
In this format, the OAL source encapsulates the original IP header
and packet body/fragment in an OAL IPv6 header. The OAL source then
adds an SRH plus Extended Fragment Header as OAL IPv6 header
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extensions for each fragment and prepends underlay headers prepared
as discussed in [I-D.templin-6man-omni3]. The OAL source sends each
such carrier packet into the SRT unsecured spanning tree, where they
may be forwarded over multiple OAL intermediate systems until they
arrive at the OAL destination. These carrier packets may themselves
be subject to fragmentation and reassembly along the concatenated
underlay network path segments.
The OMNI link control plane service distributes Client MNP prefix
information that may change occasionally due to regional node
mobility, as well as more static information for Relay FNPs that
rarely change. OMNI link Gateways and Proxy/Servers use the
information to establish and maintain a forwarding plane spanning
tree that connects all nodes on the link. The spanning tree supports
a virtual bridging service according to link layer (instead of
network layer) information, but may often include longer paths than
necessary.
Each OMNI interface therefore also includes an AERO Flow Information
Base (AFIB) that caches AERO Flow Vectors (AFVs) which can provide
both carrier packet Identification context and more direct forwarding
"shortcuts" that avoid strict spanning tree paths. As a result, the
spanning tree is always available but OMNI interfaces can often use
the AFIB entries established through route optimization to greatly
improve performance and reduce load on critical infrastructure
elements.
For OAL packets/fragments undergoing underlay re-encapsulation at an
OAL intermediate system, the OMNI interface performs underlay
decapsulation followed by Identification verification and OAL
reassembly only if the OAL packet/fragment is addressed to itself.
The OMNI interface then decrements the OAL IPv6 header Hop Limit and
discards the packet/fragment if the Hop Limit reaches 0. Otherwise,
the OMNI interface updates the OAL addresses if necessary, includes
an appropriate Identification, performs OAL fragmentation then for
each OAL fragment performs underlay encapsulation to produce a
carrier packet appropriate for next segment forwarding.
4.7. OMNI Interface Decapsulation
When an OAL node receives OAL packets/fragments addressed to another
node, it discards the previous hop underlay headers and includes new
underlay headers appropriate for the next hop in the forwarding path
to the OAL destination. The node then sends these new carrier
packets into the next hop underlay interface.
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When an OAL node receives OAL packets/fragments addressed to itself,
it performs underlay decapsulation, verifies the Identification, then
performs OAL reassembly/decapsulation to obtain the original OAL
packet or composite packet (see: [I-D.templin-6man-omni3]). Next, if
the enclosed original IP packet(s) are addressed either to itself or
to a destination reached via an interface other than the OMNI
interface, the OAL node replaces the OAL encapsulation IPv6 header
with a virtual Ethernet header and forwards the original IP packet(s)
to the network layer.
If the original IP packet(s) are destined to another node reached by
the OMNI interface, the OAL node instead decrements the Hop Limit,
then performs underlay encapsulation and forwards these new carrier
packets into an underlay interface for the next segment.
Further OMNI link decapsulation details are specified in
[I-D.templin-6man-omni3]. Further OMNI link forwarding procedures
are specified in Section 4.10.
4.8. OMNI Interface Data Origin Authentication
AERO nodes employ simple data origin authentication procedures. In
particular:
* AERO Gateways and Proxy/Servers accept carrier packets received
from the secured spanning tree.
* AERO Proxy/Servers and Clients accept carrier packets and original
IP packets that originate from within the same secured ANET.
* AERO Clients and Relays accept original IP packets from downstream
network correspondents based on ingress filtering.
* AERO Clients, Relays, Proxy/Servers and Gateways verify carrier
packet underlay encapsulation addresses according to
[I-D.templin-6man-omni3].
* OAL end systems and intermediate systems forward/accept OAL
packets/fragments with Identification values within the current
window for the OAL source neighbor for a specific underlay
interface pair and drop any packets with out-of-window
Identification values.
AERO nodes silently drop any packets that do not satisfy the above
data origin authentication procedures. Further security
considerations are discussed in Section 7.
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4.9. OMNI Interface MTU
The OMNI interface observes the link nature of tunnels, including the
Maximum Transmission Unit (MTU), Effective MTU to Receive (EMTU_R)
and the role of fragmentation and reassembly
[I-D.ietf-intarea-tunnels]. The OMNI interface employs the OAL to
accommodate multiple underlay links with diverse MTUs. OMNI
interface packet sizing considerations are specified in
[I-D.templin-6man-omni3], where the OMNI interface MTU can
essentially be considered "unlimited".
When the network layer presents an original IP packet to the OMNI
interface, the OAL source encapsulates and fragments the packet if
necessary. When the network layer presents the OMNI interface with
multiple original IP packets addressed to the same IPv6 flow, the OAL
source can concatenate them as a single OAL composite packet as
discussed in [I-D.templin-6man-omni3] before applying fragmentation.
The OAL source then submits each OAL fragment for underlay
encapsulation and transmission as a carrier packet via an underlay
interface connected to either a physical link (e.g., Ethernet, WiFi,
Cellular, etc.) or a virtual link such as an Internet or higher-layer
tunnel.
4.10. OMNI Interface Forwarding Algorithm
Original IP packets enter a node's OMNI interface either from the
network layer (i.e., from a local application or the IP forwarding
system) while carrier packets enter from the underlay (i.e., from an
OMNI interface neighbor). All original IP packets and carrier
packets entering a node's OMNI interface first undergo data origin
authentication as discussed in Section 4.8. Those that satisfy data
origin authentication are processed further, while all others are
dropped silently.
Original IP packets that enter the OMNI interface from the network
layer are forwarded to an OMNI interface neighbor using OAL
encapsulation and fragmentation to produce carrier packets for
transmission over underlay interfaces. (If forwarding state
indicates that the original IP packet should instead be forwarded
back to the network layer, the packet is dropped to avoid looping).
Carrier packets that enter the OMNI interface from the underlay are
either re-encapsulated and re-admitted into the underlay, or
reassembled and forwarded to the network layer where they are subject
to either local delivery or IP forwarding.
When the network layer of a router forwards an original IP packet
into the OMNI interface, it decrements the TTL/Hop Limit following
standard IP router conventions. Once inside the OMNI interface,
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however, the OAL does not decrement the original IP packet TTL/Hop
Limit further since its adaptation layer forwarding actions occur
below the network layer. The original IP packet's TTL/Hop Limit will
therefore be the same when it exits the destination OMNI interface as
when it first entered the source OMNI interface.
When an OAL intermediate system receives a carrier packet, it
performs underlay decapsulation to obtain the enclosed OAL packet/
fragment. When the intermediate system forwards an OAL packet/
fragment not addressed to itself (or one addressed to itself but that
also includes an SRH with Segments Left greater than 0), it
decrements the OAL Hop Limit without decrementing the network layer
IP TTL/Hop Limit. If decrementing would cause the OAL Hop Limit to
become 0, the OAL intermediate system drops the OAL packet/fragment.
This ensures that original IP packet(s) cannot enter an endless loop.
OMNI interfaces may have multiple underlay interfaces and/or NCEs for
neighbors with multiple underlay interfaces (see: Section 4.3). The
OAL uses Interface Attributes and/or Traffic Selectors to select an
outbound underlay interface for each OAL packet and also to select
underlay network Destination Addresses based on the neighbor's target
underlay interfaces. AERO implementations SHOULD permit network
management to dynamically adjust Traffic Selector values at runtime.
If an OAL packet/fragment matches the Interface Attributes and/or
Traffic Selectors of multiple outgoing interfaces and/or neighbor
interfaces, the OMNI interface replicates the packet and sends a
separate copy via each of the (outgoing / neighbor) interface pairs;
otherwise, it sends a single copy via an interface with the best
matching attributes/selectors. (While not strictly required, the
likelihood of successful reassembly is often greatest when the OMNI
interface sends all fragments of the same fragmented OAL packet/
fragment consecutively over the same underlay interface pair to avoid
complicating factors such as delay variance and reordering.) AERO
nodes keep track of which underlay interfaces are currently
"reachable" or "unreachable", and use only "reachable" interfaces for
forwarding purposes.
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In addition to standard forwarding based on Interface Attributes and/
or Traffic Selectors, nodes may employ a policy engine that would
provide further guidance to the forwarding algorithm. For example
the policy engine may suggest a load balancing profile over multiple
underlay interface pairs, with portions of a traffic flow spread
between multiple paths according to Equal Cost MultiPath or Link
Aggregation Groups (LAGs) [RFC6438] (note that Interface Attributes
include an underlay interface group identifier). Other policies may
suggest the use of paths with the least cost, best performance, etc.
This document therefore specifies mechanisms without mandating any
particular policies.
All Clients, Proxy/Servers and Gateways serve as OAL intermediate
nodes for the purpose of forwarding OAL packets/fragments that
include an SRH or OCH with non-zero AFVI over the unsecured spanning
tree based on AFIB entries. When an OAL intermediate node forwards
an OAL packet/fragment with an underlay Source Address and AFVI that
matches an AFV, the node first verifies that the Identification is in
sequence. The OAL intermediate node then rewrites the packet's AFVI
with a value that will be recognized by the next OAL hop and forwards
the packet. (For OAL packets/fragments with uncompressed headers and
with AFVI set to 0, the OAL intermediate node instead forwards based
on matching the OAL IPv6 Destination Address with a standard IPv6
forwarding table entry after applying SRH processing.) The chain of
OAL source, intermediate and destination nodes may therefore traverse
many (Proxy/)Clients, Proxy/Servers and Gateways on the path.
The following sections discuss the OMNI interface-specific forwarding
algorithms for Clients, Proxy/Servers and Gateways. In the following
discussion, an original IP packet's Destination Address is said to
"match" if it is the same as a cached address, or if it is covered by
a cached FNP/MNP.
4.10.1. Client Forwarding Algorithm
When the network layer presents an original IP packet to a Client's
OMNI interface (i.e., following next-hop determination), the Client
forwards the packet to the OMNI interface virtual router function if
the Destination is off-link. The virtual router then either forwards
the packet to a Proxy/Server or initiates adaptation layer address
resolution and forwards the packet according to ALNCE information.
If the Destination is on-link, the Client instead invokes network
layer address resolution if there is no NLNCE. The Client holds the
packet in a queue until address resolution completes, then admits the
packet into the OMNI interface. The OMNI interface then searches for
an ALNCE that matches the Destination. If there is a matching ALNCE
for a neighbor reached via a *NET interface (i.e., an upstream
interface), the Client selects one or more "reachable" neighbor
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interfaces in the entry for forwarding purposes.
When a carrier packet enters a Client's OMNI interface from the
underlay, the Client performs underlay decapsulation if necessary to
obtain the OAL packet/fragment then examines the OAL Destination
Address (i.e., after locating the correct AFV if the OAL packet
header is OCH). If the OAL Destination Address matches one of the
Client's addresses and the packet includes an SRH with Segments Left
greater than 0, the Client rewrites the OAL Destination Address and
forwards the packet to the peer Client or Proxy/Server indicated by
the next hop SRH address. Otherwise, the Client (acting as an OAL
destination) verifies that the Identification is in-window for the
matching AFV, then reassembles/decapsulates as necessary and delivers
the original IP packet to the network layer. If the OAL Destination
Address does not match, the Client drops the original IP packet and
MAY return a network layer ICMP Destination Unreachable message
subject to rate limiting (see: Section 4.11).
Note: The forwarding table entries established in peer Clients are
based on MLAs which also appear as OAL Source or Destination
Addresses within (M)ANETs. The original IP packet Source and
Destination Addresses instead use MNP or MLA addresses.
Note: Clients within MANETs support Client-to-Client multihop
forwarding when necessary to reach destinations or FHS Proxy/Servers
that may be multiple OAL hops away. In this way, forwarding Clients
act as OAL intermediate nodes and forward using OCH compression based
on AFV state that is indexed by the AFVIs included in each OAL
packet/fragment.
4.10.2. Proxy/Server and Relay Forwarding Algorithm
When the network layer admits an original IP packet into a Proxy/
Server's OMNI interface, the OAL drops the packet to avoid looping if
forwarding state indicates that it should be forwarded back to the
network layer. Otherwise, the OAL examines the IP Destination
Address to determine if it matches the MLA of a neighboring Gateway
found in the OMNI interface's network layer neighbor cache. If so,
the Proxy/Server performs OAL encapsulation and fragmentation then
performs underlay encapsulation and forwards the resulting carrier
packet to the Gateway over a secured link (e.g., an IPsec tunnel,
Direct link, etc.) to support control plane functions such as the
operation of the BGP routing protocol. If the IP Destination Address
matches an FNP/MNP associated with a (foreign) Proxy/Server or
Client, the (local) Proxy/Server instead assumes the Relay role and
forwards the original IP packet in the same manner as for Client
forwarding while including an SRH. Specifically, if there is a
matching NCE the Proxy/Server selects one or more "reachable"
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neighbor interfaces in the entry for forwarding purposes; otherwise,
the Proxy/Server performs OAL encapsulation/fragmentation followed by
underlay encapsulation and forwards the resulting carrier packets
while invoking address resolution and multilink forwarding procedures
per Section 4.13.
When the Proxy/Server receives carrier packets on underlay interfaces
that contain OAL packets/fragments with both a Source and Destination
OAL Address that correspond to the same Client's MLA, the Proxy/
Server drops the carrier packets regardless of their OMNI link point
of origin. The Proxy/Server also drops original IP packets received
on underlay interfaces either directly from a *NET Client if the
original IP Destination Address corresponds to the same Client's
delegated MNP. Proxy/Servers also drop carrier packets that contain
OAL packets/fragments with foreign OAL Destination Addresses (MLAs)
that do not match one of their local *NET Clients. These checks are
essential to prevent forwarding inconsistencies from accidentally or
intentionally establishing endless loops that could congest nodes
and/or *NET links.
Proxy/Servers process carrier packets that contain OAL packets/
fragments with OCH headers or with Destination Addresses that match
their MLA and also include an SRH. In the first case, the Proxy/
Server examines the underlay Source Address and AFVI to locate the
corresponding AFV entry in the AFIB. In the second case, the Proxy/
Server applies standard SRH processing procedures. The Proxy/Server
then forwards them according to the AFV or IPv6 routing state while
decrementing the OAL packet/fragment Hop Limit.
For OAL packets/fragments with Destination Addresses that match their
MLA and also include an SRH, the Proxy/Server performs any necessary
local processing then rewrites the OAL Destination Address according
to the next hop SRH address. For those that do not include an OCH or
SRH with additional next hop addresses, the Proxy/Server instead
performs underlay decapsulation, verifies the Identification and
performs OAL reassembly to obtain the original IP packet. For data
packets addressed to its own MLA that arrived via the secured
spanning tree, the Proxy/Server delivers the original IP packet to
the network layer to support secured BGP routing protocol control
messaging. For data packets originating from one of its dependent
Clients, the Proxy/Server instead performs OAL encapsulation/
fragmentation followed by underlay encapsulation and sends the
resulting carrier packets while invoking address resolution and
multilink forwarding procedures per Section 4.13. For control
messages, the Proxy/Server instead authenticates the message and
processes it as specified in later sections of this document while
updating neighbor cache and/or AFIB state accordingly.
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When the Proxy/Server receives carrier packets that contain OAL
packets with OAL Destination Address set to the MLA of one of its
Client neighbors established through RS/RA exchanges, it accepts the
carrier packets only if data origin authentication succeeds. If the
NCE state is DEPARTED, the Proxy/Server changes the OAL Destination
Address to the MLA of the Client's new Proxy/Server, decrements the
OAL Hop Limit, then performs underlay encapsulation and forwards the
resulting carrier packets into the spanning tree which will
eventually deliver them to the new Proxy/Server. If the neighbor
cache state for the Client is REACHABLE and the Proxy/Server is a MAP
responsible for serving as the Client's address resolution responder
and/or default router, it verifies the Identification then submits
the OAL packet/fragment for reassembly. The Proxy/Server then
decapsulates and processes the resulting control message or original
IP packet accordingly. Otherwise, the Proxy/Server changes the OAL
Destination Address to the local Client's MLA, includes an SRH with
intermediate hop MLAs, decrements the OAL Hop Limit, performs
underlay encapsulation and forwards the carrier packet to the Client
which then performs data origin verification and reassembly. (In the
mobility case, the Client may receive fragments of the same original
IP packet from different Proxy/Servers but this will not interfere
with correct reassembly.)
When the Proxy/Server receives carrier packets that contain OAL
packets with OAL Source Address set to the MLA of one of its Client
neighbors established through RS/RA exchanges, it accepts the carrier
packets only if data origin authentication succeeds. The local
Proxy/Server then forwards the packet according to the IP destination
or AFVI state previously established through multilink control
messaging.
When the Proxy/Server receives carrier packets that contain OAL
packets with OAL Destination Address set to a FNP address that does
not match the MSP, it accepts the carrier packets only if data origin
authentication succeeds and if there is a network layer forwarding
table entry for the FNP. The Proxy/Server then performs underlay
decapsulation, verifies the Identification, performs OAL reassembly/
decapsulation to obtain the original IP packet, then presents it to
the network layer (as a Relay) where it will be delivered according
to standard IP forwarding.
When a Proxy/Server receives a carrier packet from the secured
spanning tree, it considers the message as authentic without having
to verify network or higher layer authentication signatures.
If the Proxy/Server has multiple original IP packets to send to the
same neighbor, it can concatenate them as a single OAL composite
packet [I-D.templin-6man-omni3].
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4.10.3. Gateway Forwarding Algorithm
When the network layer admits an original IP packet into the
Gateway's OMNI interface, the OAL drops the packet if routing
indicates that it should be forwarded back to the network layer to
avoid looping. Otherwise, the Gateway examines the IP Destination
Address to determine if it matches the MLA of a neighboring Gateway
or Proxy/Server by examining the OMNI interface's network layer
neighbor cache. If so, the Gateway performs OAL encapsulation/
fragmentation followed by underlay encapsulation and forwards the
resulting carrier packets to the neighboring Gateway or Proxy/Server
over a secured link (e.g., an IPsec tunnel, etc.) to support the
operation of control plane functions (including the BGP routing
protocol) between OAL neighbors.
Gateways forward OAL packets/fragments reassembled from spanning tree
carrier packets while decrementing the OAL Hop Limit but not the
original IP header TTL/Hop Limit. Gateways send carrier packets that
contain OAL packets/fragments with critical BGP routing protocol or
other control messages via the SRT secured spanning tree, and may
send other carrier packets via the secured/unsecured spanning tree or
via more direct paths according to AFIB information. When the
Gateway receives a carrier packet, it decapsulates to obtain the OAL
packet/fragment then searches for an AFIB entry that matches the OAL
AFVI or an IPv6 forwarding table entry that matches the OAL
Destination Address.
Gateways process carrier packets containing OAL packets/fragments
with OAL Destination Addresses that do not match their MLAs in the
same manner as for traditional IP forwarding within the OAL, i.e.,
they forward packets not explicitly addressed to themselves.
Gateways locally process OAL packets/fragments with OCH headers or
full OAL headers with their MLA as the OAL Destination Address. If
the OAL packet/fragment contains an OCH or a full OAL header with an
SRH extension, the Gateway forwards the OAL packet/fragment to the
next hop while decrementing the OAL Hop Limit but without
reassembling. When the Gateway forwards the OAL packet/fragment, it
either rewrites the OCH AFVI with the value it will represent to the
next OAL hop or follows standard SRH processing procedures.
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If the OAL packet/fragment includes a full OAL header but does not
include an AFVI, the Gateway instead examines the OAL packet. The
Gateway first determines whether the OAL packet includes an MP
message then processes the message according to the multilink
forwarding procedures discussed in Section 4.13. If the carrier
packets arrived over the secured spanning tree and the enclosed OAL
packets/fragments are addressed to its MLA, the Gateway instead
reassembles then discards the OAL header and forwards the original IP
packet to the network layer to support secured BGP routing protocol
control messaging. The Gateway instead drops all other OAL packets.
Gateways forward OAL packets/fragments received in carrier packets
that arrived from a first segment via the secured spanning tree to
the next segment also via the secured spanning tree. Gateways
forward OAL packets/fragments received in carrier packets that
arrived from a first segment via the unsecured spanning tree to the
next segment also via the unsecured spanning tree. Gateways
configure an IPv6 routing table that determines the next hop for a
given OAL Destination Address, where the secured/unsecured spanning
tree is determined through the selection of the underlay interface to
be used for transmission (e.g., an IPsec tunnel or an open INET
interface).
As for Proxy/Servers, Gateways must verify that the underlay Source
Addresses of carrier packets not received from the secured spanning
tree are "trusted" before forwarding according to an AFV (otherwise,
the carrier packet must be dropped).
4.11. OMNI Interface Error Handling
When an AERO node admits an original IP packet into the OMNI
interface, it may receive link and/or network layer error
indications. The AERO node may also receive OMNI link error
indications in OAL-encapsulated uNA messages that include
authentication signatures.
A link layer error indication is an ICMP error message generated by a
router in an underlay network on the path to the next OAL hop or by
the next OAL hop itself. The message includes an IP header with the
address of the node that generated the error as the Source Address
and with the underlay address of the AERO node as the Destination
Address.
The IP header is followed by an ICMP header that includes an error
Type, Code and Checksum. Valid type values include "Destination
Unreachable", "Packet Too Big", "Time Exceeded", "Parameter Problem"
etc. [RFC0792][RFC4443].
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The ICMP header is followed by the leading portion of the carrier
packet that generated the error, also known as the "packet-in-error".
For ICMPv6, [RFC4443] specifies that the packet-in-error includes:
"As much of invoking packet as possible without the ICMPv6 packet
exceeding the minimum IPv6 MTU" (i.e., no more than 1280 bytes). For
ICMPv4, [RFC0792] specifies that the packet-in-error includes:
"Internet Header + 64 bits of Original Data Datagram", however
[RFC1812] Section 4.3.2.3 updates this specification by stating: "the
ICMP datagram SHOULD contain as much of the original datagram as
possible without the length of the ICMP datagram exceeding 576
bytes".
The link layer error message format is shown in Figure 4:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ IP Header of link layer ~
~ error message ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ICMP Header ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ---
| | P
~ carrier packet underlay and ~ a
~ OAL encapsulation headers ~ c
| | k
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ e
| | t
~ original IP packet hdrs ~
~ (first-fragment only) ~ i
| | n
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | e
~ Portion of the body of ~ r
~ the original IP packet ~ r
~ (all fragments) ~ o
| | r
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ---
Figure 4: OMNI Interface Link-Layer Error Message Format
The AERO node rules for processing these link layer error messages
are as follows:
* When an AERO node receives a link layer Parameter Problem message,
it processes the message the same as described as for ordinary
ICMP errors in the normative references [RFC0792][RFC4443].
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* When an AERO node receives persistent link layer Packet Too Big
messages, there may be a restricting link on the path or the next
OAL hop may be experiencing reassembly cache congestion. In both
cases, the node should adaptively decrease the size of the OAL
fragments it sends to this OAL next hop (note that the PTB
messages could indicate either "hard" or "soft" errors).
* When an AERO node receives persistent link layer Time Exceeded
messages, the IP ID field may be wrapping before earlier fragments
awaiting reassembly have been processed. In that case, the node
should adaptively decrease the size of the OAL fragments it sends
to this OAL next hop.
* When an AERO node receives persistent link layer Destination
Unreachable messages in response to carrier packets that it sends
to one of its neighbor correspondents, the node should process the
message as an indication that a path may be failing, and
optionally initiate NUD over that path. If it receives
Destination Unreachable messages over multiple paths, the node
should allow future carrier packets destined to the correspondent
to flow through a default route and re-initiate route
optimization.
* When an AERO Client receives persistent link layer Destination
Unreachable messages in response to carrier packets that it sends
to one of its neighbor Proxy/Servers, the Client should mark the
path as unusable and use another path. If it receives Destination
Unreachable messages on many or all paths, the Client should
associate with a new Proxy/Server and release its association with
the old Proxy/Server as specified in Section 4.15.3.
* When an AERO Proxy/Server receives persistent link layer
Destination Unreachable messages in response to carrier packets
that it sends to one of its neighbor Clients, the Proxy/Server
should mark the underlay path as unusable and use another underlay
path.
* When an AERO Proxy/Server receives link layer Destination
Unreachable messages in response to a carrier packet that it sends
to one of its permanent neighbors, it treats the messages as an
indication that the path to the neighbor may be failing. However,
the dynamic routing protocol should soon re-converge and correct
the temporary outage.
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When an AERO Gateway receives a carrier packet for which the network
layer Destination Address is covered by an MSP assigned to a black-
hole route, the Gateway drops the carrier packet if there is no more-
specific routing information for the destination and returns an OMNI
interface Destination Unreachable message subject to rate limiting.
AERO nodes include ICMPv6 error messages intended for an OAL source
as sub-options in the OMNI option of secured uNA messages. When the
OAL source receives the uNA message, it can extract the ICMPv6 error
message enclosed in the OMNI option and either process it locally or
translate it into a network layer error to return to the original
source.
An AERO/OMNI intermediate system may discover that a transit packet
has no matching AFIB state to support forwarding to the next
adaptation layer hop. In that case, the intermediate system should
return a Destination Unreachable error sub-option in a secured uNA
message. The OAL source should process the message as an indication
that AFIB multilink forwarding state for a particular flow must be
refreshed.
4.12. AERO Mobility Service Coordination
AERO nodes observes the Router Discovery and Prefix Registration
specifications and coordinate their autoconfiguration actions with
the mobility service through RS/RA message exchanges as specified in
[I-D.templin-6man-omni3].
4.12.1. AERO Service Model
Each AERO Proxy/Server on the OMNI link is configured to respond to
Client MNP prefix delegation/registration requests based on the
DHCPv6 service. Each Proxy/Server is provisioned with a database of
MNP-to-Client ID mappings for all Clients enrolled in the AERO
service. The Client database is maintained by a central
administrative authority for the OMNI link and securely distributed
to all Proxy/Servers, e.g., via the Lightweight Directory Access
Protocol (LDAP) [RFC4511], via static configuration, etc. Clients
receive the same MNP service regardless of the Proxy/Servers they
select and provision their MNPs for downstream-attached node
addressing on EUN interfaces. (Note: an OMNI link can instead
delegate non-correlated MNPs to Clients instead of maintaining a
common synchronized database. In that case, each Client may receive
a different MNP delegation each time it registers with the OMNI
domain and may need to renumber its downstream-attached EUNs.)
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Clients associate each of their *NET underlay interfaces with FHS
Proxy/Servers. Each FHS Proxy/Server locally services one or more of
the Client's underlay interfaces, and the Client typically selects
one among them to serve as the MAP Proxy/Server (the Client may
instead select a "third-party" MAP Proxy/Server that does not
directly service any of its underlay interfaces). All of the
Client's other FHS Proxy/Servers forward proxyed copies of RS/RA
messages between the MAP Proxy/Server and Client without assuming the
MAP role functions themselves.
Each Client typically associates with a single MAP Proxy/Server,
while all other Proxy/Servers are candidates for providing the MAP
role for other Clients. A Client can select both an FHS and MAP
Proxy/Server in a single message by including an SRH in the RS
message OAL header when it already knows the MAP's address. An FHS
Proxy/Server assumes the MAP role when it receives an RS message with
a Destination Address that matches its own MLA or link-scoped All-
Routers multicast. An FHS Proxy/Server assumes the proxy role when
it receives an RS message with an SRH or with a Destination Address
that matches another Proxy/Server. (An FHS Proxy/Server can also
assume the proxy role when it receives an RS message addressed to
link-scoped All-Routers multicast if it can determine the MLA of
another Proxy/Server to serve as a MAP.)
AERO Clients and Proxy/Servers use control messages to maintain
NLNCEs and ALNCEs. AERO Proxy/Servers configure their OMNI
interfaces as advertising NBMA interfaces, and therefore send unicast
RA messages with a short Router Lifetime value (e.g., 2 *
ReachableTime seconds) in response to a Client's RS message.
Thereafter, Clients send additional RS messages to keep Proxy/Server
state alive.
AERO Clients and FHS/MAP Proxy/Servers include MNP prefix delegation
parameters in RS/RA messages. The control messages are exchanged
between the Client and any FHS Proxy/Servers acting as proxys for the
MAP Proxy/Server as specified in [I-D.templin-6man-omni3] according
to the address/prefix management schedule required by the service.
If the Client knows its MNP in advance, it can include the MNP in its
prefix delegation request. If the MAP Proxy/Server accepts the
Client's MNP assertion (or if it delegates a new MNP for the Client),
it injects the MNP into the routing system and establishes the
necessary neighbor cache state.
AERO Clients and their FHS Proxy/Servers on MANETs and open INETs
must establish and maintain Identification synchronization windows in
their RS/RA exchanges. The window synchronization provides a well-
managed Identification value that the Client and Proxy/Server can use
for validating control messages with authentication signatures.
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All Client and Proxy/Server behaviors for the exchange of RS/RA
messages are conducted according to the Router Discovery and Prefix
Delegation specifications found in [I-D.templin-6man-omni3].
4.13. AERO Address Resolution, Multilink Forwarding and Route
Optimization
AERO nodes invoke address resolution, multilink forwarding and route
optimization when they need to forward the initial original IP
packets of flows to new neighbors over (M)ANET/INET interfaces as
well as to maintain continuous multilink forwarding coordination with
existing neighbors. As specified in [RFC4861], "when a node has a
unicast packet to send to a neighbor, but does not know the
neighbor's link-layer address, it performs address resolution".
Possible Source and Destination Addresses for original IP packets
that traverse a local (M)ANET/INET and/or the rest of the OMNI link
include addresses taken from an FNP, MNP or MLA assigned to a Client.
The flow is then identified by the 3-tuple consisting of the IPv6
Source Address, Destination Address and Flow Label.
The Address Resolution Source (ARS) considers candidate original IP
packet destinations as either on-link or off-link on the OMNI
interface. For destinations that match an on-link prefix, the ARS
invokes address resolution as a network layer function if there is no
NLNCE matching the destination. For destinations that match an off-
link prefix, the ARS forwards the packet to a virtual router function
within the OMNI interface that invokes address resolution as an
adaptation layer function if there is no ALNCE matching the
destination. The first such address resolution may return prefix
information sufficient to satisfy future resolutions for addresses
covered by the same prefix locally and without the need for
additional control messaging over the network.
Address resolution is based on an IPv6 ND NS/NA(AR) messaging
exchange between the ARS and the target neighbor as the Address
Resolution Target (ART). The ARS engages address resolution by
sending NS(AR) messages over a selected underlay interface to
determine adaptation and underlay address mappings for the ART
network layer address. (The ARS may select any available underlay
interface to carry the NS(AR) with a likely emphasis on the best
performing, least congested, etc.)
The ARS then discovers address resolution information from any OMNI
Interface Attributes sub-options included in NA(AR) messages returned
by the ART. Both the ARS and ART can update their neighbor caches
based on the address resolution information and cache any information
received in Route Information Options (RIOs) [RFC4191] included in
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the NS/NA(AR) exchange. Note that the NS/NA(AR) RIOs are included as
adaptation layer information in the OMNI option per
[I-D.templin-6man-omni3] and are not delivered to the network layer.
The original source or its current FHS/MAP Proxy/Server serves as the
ARS. Either the ART itself or the current LHS/MAP Proxy/Server (or
Relay) for the ART serves as the Address Resolution Responder (ARR),
i.e., the NA(AR) source.
Address resolution is initiated by the first eligible ARS closest to
the original source as follows:
* For Clients on VPN/IPsec and Direct interfaces, the Client's FHS
Proxy/Server is the ARS.
* For Clients on (M)ANET interfaces, either the FHS Proxy/Server or
the Client itself may be the ARS.
* For Clients on INET interfaces, the Client itself is the ARS.
* For FNP correspondent nodes on foreign links/networks serviced by
a Relay, the Relay is the ARS.
* For Clients that engage the MAP Proxy/Server in "mobility anchor"
mode, the MAP Proxy/Server is the ARS.
* For peer Clients within the same (M)ANET/EUN, address resolution
and route optimization is through receipt of Redirect messages.
The AERO routing system directs an address resolution request sent by
the ARS to the ARR. The ARR then returns an address resolution reply
which must include information that is complete, current, consistent
and authentic. Both the ARS and ARR are then jointly responsible for
periodically refreshing the address resolution, and for quickly
informing each other of any changes. Following address resolution,
the ARS and ART perform subsequent multilink forwarding and route
optimization exchanges to maintain optimal forwarding profiles for
each distinct flow.
The address resolution, multilink forwarding and route optimization
procedures are specified in the following sections.
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4.13.1. Multilink Address Resolution
Address resolution over OMNI interfaces is conceptually the same as
specified in Section 7 of [RFC4861] including the sending and
receiving of NS/NA(AR) messages as well as their implications for
neighbor cache entry creation and state management. The NS/NA(AR)
messages include addresses and S/TLLAOs in the same manner as for any
interface and as discussed in Section 4.5.1. The OMNI interface
therefore exhibits an IP layer behavior that is indistinguishable
from an ordinary interface while managing adaptation layer state at a
layer below IP.
For destinations that match an off-link prefix, Address Resolution
over OMNI interfaces is driven by NS/NA(AR) messaging as an
adaptation layer function without disturbing the NLNCE. The network
layer forwards packets that match an off-link prefix to a virtual
router function within the OMNI interface. The virtual router
function then either forwards the packets to an FHS Proxy/Server to
act as the ARS or initiates an NS/NA(AR) exchange at the adaptation
layer (without including S/TLLAOs) while acting as an ARS on its own
behalf. In that case, the OMNI interface caches any updated
adaptation layer addressing information received in NS/NA(AR)
messages in the ALNC.
For destinations that match an on-link prefix, Address Resolution
over OMNI interfaces is driven by network layer NS/NA(AR) messaging
the same as for any IP interface. The OMNI interface then removes
the S/TLLAO upon transmission of all NS/NA(AR) messages and includes
an S/TLLAO with the OMNI interface internal link-layer address when
delivering an NS/NA(AR) message to the network layer.
When one or more original IP packets matching an on-link prefix are
forwarded over an OMNI interface, the ARS checks the Destination
Cache to determine whether there is a NCE that matches the
Destination Address. If there is a NCE in the REACHABLE state, the
ARS invokes the OAL and forwards the resulting carrier packets
according to the cached state then returns from processing. If there
is no NLNCE but the ARS is able to determine that adaptation layer
mapping state for the IP destination is available, e.g., by snooping
the ALNC, it can also create a NLNCE in the REACHABLE state and admit
the original IP packets into the interface without requiring an NS/
NA(AR) exchange.
Otherwise, if there is no NLNCE the ARS creates one in the INCOMPLETE
state. The ARS then prepares an Address Resolution NS(AR) message to
send toward an ART. The resulting NS(AR) message must be sent
securely and includes Source, Destination and Target Addresses as
discussed in Section 4.5.1.
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When the ARS admits the NS(AR) message into the OMNI interface, the
adaptation layer returns an immediate NA(AR) if the ALNC already
contains fresh address resolution information for the FNP/MNP prefix
or MLA that covers the IP Destination Address. Otherwise, the
adaptation layer prepares to forward the NS(AR) while removing the
SLLAO (if present) since the locally-unique link-layer address has no
useful information for prospective neighbors.
For both the on-link and off-link cases of forwarding an NS(AR) at
the adaptation layer, the ARS then includes an OMNI option with an
authentication sub-option (if necessary). If the ARS can commit to
managing its own dynamic mobility updates, it then includes Interface
Attributes and/or Traffic Selectors for all of the source Client's
underlay interfaces plus RIOs for any of the Client's MNPs. The ARS
then then submits the NS(AR) message for OAL encapsulation and
transmission.
4.13.1.1. Sending the NS(AR)
When the ARS is a FHS Proxy/Server, it sets the OAL Source Address to
its own MLA and sets the OAL Destination Address to the NS(AR) Target
Address. The ARS then performs underlay encapsulation and sends the
resulting carrier packet into the SRT secured spanning tree without
decrementing the network layer TTL/Hop Limit field.
When the ARS is a Client, it instead uses its own MLA as the OAL
Source Address and the MLA of the next OAL hop as the OAL Destination
Address while including an SRH with the MLAs of OAL intermediate
systems ending with the MLA of the interface-specific FHS Proxy/
Server. If the Client is in a MANET or an open INET, it next
calculates and includes an authentication signature. In all *NET
cases, the Client then includes an OAL IPv6 Extended Fragment Header
with Identification set to an in-window value for this FHS Proxy/
Server. The ARS Client then performs underlay encapsulation and
forwards the carrier packet to the FHS Proxy/Server.
The FHS Proxy/Server then performs underlay decapsulation, verifies
the Identification, verifies the NS(AR) OAL checksum/authentication
signature and confirms that the Client's claimed FNP/MNP RIO(s) and
Source Address are correct. The FHS Proxy/Server then changes the
OAL Source Address to its own MLA and changes the OAL Destination
Address to the NS(AR) Target Address. The FHS Proxy/Server next
removes the IPv6 Extended Fragment Header, performs underlay
encapsulation and sends the resulting carrier packet into the secured
spanning tree on behalf of the Client.
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Note: both the source and target Client/Relay and their MAP Proxy/
Servers include current and accurate information for their multilink
Interface Attributes profile. The MAP Proxy/Servers can be trusted
to provide an authoritative ARR response and/or mobility update
message on behalf of the source/target if necessary.
4.13.1.2. Relaying the NS(AR)
When a Gateway receives carrier packets containing the NS(AR), it
performs underlay decapsulation and determines the next hop by
consulting its standard IPv6 forwarding table for the OAL header
Destination Address. The Gateway next decrements the OAL header Hop
Limit, performs underlay encapsulation and sends the carrier
packet(s) via the secured spanning tree the same as for any IPv6
router where they may traverse multiple intermediate OMNI link
segments interconnected by Gateways. The final Gateway will deliver
the carrier packets via the secured spanning tree to the LHS/MAP
Proxy/Server (or Relay) that services the ART.
4.13.1.3. NS(AR) Processing at the ARR/ART
When the LHS/MAP Proxy/Server (or Relay) of the ART receives the
NS(AR) secured carrier packets with the target address of the ART as
the OAL Destination Address, it performs underlay decapsulation then
either forwards the NS(AR) to the ART or processes it locally if it
is acting as the ART's designated ARR. The LHS/MAP Proxy/Server (or
Relay) processes the message as follows:
* if the NS(AR) target matches a Client NCE in the DEPARTED state,
the (old) MAP Proxy/Server resets the OAL Destination Address to
the MLA of its new MAP Proxy/Server. The old MAP Proxy/Server
then decrements the OAL header Hop Limit, performs underlay
encapsulation and forwards the resulting carrier packet over the
secured spanning tree.
* If the NS(AR) target matches a Client NCE in the REACHABLE state,
the LHS/MAP Proxy/Server (or Relay) notes whether the NS(AR)
arrived from the secured spanning tree. If the message arrived
via the secured spanning tree the LHS/MAP Proxy/Server (or Relay)
verifies the NS(AR) OAL checksum only; otherwise, it must also
verify the authentication signature.
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* If the LHS/MAP Proxy/Server maintains a Report List for the ART
(see: [I-D.templin-6man-omni3]), it next records the NS(AR) Source
Address in the Report List for this ART. If the MAP Proxy/Server
is the ART's designated ARR, it forwards any original IP packet(s)
attached to the NS(AR) composite packet to the ART and prepares to
return an NA(AR) as discussed below; otherwise, the LHS/MAP Proxy/
Server determines the underlay interface for the ART and proceeds
as follows:
- If the LHS/MAP Proxy/Server is also the LHS Proxy/Server on the
underlay interface used to convey the NS(AR) to the ART, it
includes an OAL IPv6 Extended Fragment Header with an in-window
Identification for the ART Client plus an SRH and
authentication signature if necessary then recalculates the OAL
checksum. The Proxy/Server then changes the OAL Source Address
to its own MLA, changes the OAL Destination Address to the next
hop MLA on the path to the ART, decrements the OAL Hop Limit,
performs underlay encapsulation and forwards the resulting
carrier packet over the underlay interface to the ART.
- If the MAP Proxy/Server is not the LHS Proxy/Server on the
underlay interface used to convey the NS(AR) to the ART, it
instead changes the OAL Destination Address to the MLA of the
LHS Proxy/Server for the selected ART interface. The MAP
Proxy/Server next decrements the OAL Hop Limit, performs
underlay encapsulation and forwards the resulting carrier
packet over the secured spanning tree.
- When the LHS Proxy/Server receives the carrier packets, it
performs underlay decapsulation, verifies the NS(AR) OAL
checksum, then forwards to the ART while changing the OAL
addresses as above. The LHS Proxy/Server also includes an IPv6
Extended Fragment Header plus an SRH and authentication
signature if necessary while recalculating the checksum the
same as described above.
* If the NS(AR) target matches one of its FNP routes, the MAP/LHS
Proxy/Server serves as both a Relay and an ARR, since the Relay
forwards original IP packets toward FNP target nodes at the
network layer.
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If the ARR is a Relay or the ART itself, it first creates or updates
an ALNCE for the NS(AR) Source MLA while caching all Interface
Attributes and Traffic Selector information in the ALNCE and caching
any IPv6 addresses for the original source found in the Interface
Attributes in the Destination Cache. The ARR then installs any RIO
MNP prefixes in the ALNCE. (If the NS(AR) does not include address
resolution information, the ART will simply need to initiate another
unidirectional address resolution request if it has return traffic to
send back to the ARS.)
Next, if the NS(AR) target is on-link on the ARR/ART's OMNI interface
the ART delivers the NS(AR) to the network layer while including an
SLLAO with the OMNI interface internal link-layer address. The
network layer will return an NA(AR) with a TLLAO which the ARR
removes before forwarding the NA(AR) back to the ARS. For off-link
targets, the ARR instead prepares a solicited NA(AR) message to
return to the ARS as an adaptation layer function without exposing
the NS(AR) to the network layer.
In both the on- and off-link cases, the ARR includes RIOs for all of
the ART's FNPs/MNPs, where the RIO for a destination that matches
only "default" includes a /64 FNP that covers the address. The ARR
then includes Interface Attributes and Traffic Selector sub-options
for all of the ART's underlay interfaces with current information for
each interface. The ARR next sets the NA(AR) message R flag to 1 (as
a router) and S flag to 1 (as a response to a solicitation) and sets
the O flag to 1 (as an authoritative responder).
The ARR finally includes an authentication signature, an IPv6
Extended Fragment Header and an OAL SRH with MLA addressing
information for the LHS hops on the path to the LHS Proxy/Server and
ending with the MNP of the ARS MAP/FHS Proxy/Server that appeared in
the NS(AR) SRH. The ARR next calculates the NA(AR) OAL checksum then
submits the NA(AR) for encapsulation with OAL Source Address set to
its own MLA and Destination Address set to either the MLA that
appeared in the NS(AR) OAL source for (M)ANET traversal or the NS(AR)
source itself for INET traversal. The ARR then performs underlay
encapsulation and forwards the resulting carrier packet.
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When the ART's LHS Proxy/Server receives carrier packets sent by an
ART acting as an ARR on its own behalf, it performs underlay
decapsulation then verifies the NA(AR) message OAL Identification and
checksum/authentication signature. The Proxy/Server then verifies
that any RIO information is acceptable, changes the OAL Source
Address to its own MLA and changes the OAL Destination Address to the
MLA of the ARS MAP/FHS Proxy/Server. The Proxy/Server next
decrements the OAL Hop Limit, removes the OAL Extended Fragment
Header, performs underlay encapsulation and finally forwards the
resulting carrier packet into the secured spanning tree.
4.13.1.4. Relaying the NA(AR)
When a Gateway receives NA(AR) carrier packets, it performs underlay
decapsulation and determines the next hop by consulting its standard
IPv6 forwarding table for the OAL header Destination Address. The
Gateway then decrements the OAL header Hop Limit, performs underlay
encapsulation and forwards the resulting carrier packet via the SRT
secured spanning tree where it may traverse multiple intermediate
OMNI link segments interconnected by other Gateways. The final-hop
Gateway will deliver the carrier packets via the secured spanning
tree to a FHS Proxy/Server for the ARS.
4.13.1.5. Processing the NA(AR) at the ARS
When the ARS receives NA(AR) carrier packets, it performs underlay
decapsulation then searches for an ALNCE that matches the MLA
corresponding to the NA(AR) Source. The ARS then processes the
message the same as for standard IPv6 Address Resolution [RFC4861].
In the process, it caches all OMNI option Interface Attributes and
Traffic Selectors in the ALNCE for the NA(AR) MLA Source Address and
caches any IPv6 addresses for the ART found in the Interface
Attributes in the Destination Cache. The ARS then caches any RIO
FNP/MNP prefixes in the ALNCE indexed by the neighbor's MLA. All
included Interface Attributes sub-options plus RIOs together provide
the address mapping information necessary to satisfy address
resolution.
For targets that match an on-link prefix, the adaptation layer of the
ARS then includes a TLLAO with the OMNI interface internal link-layer
address then delivers the NA(AR) to the network layer. The network
layer will then set the NLNCE for this neighbor to REACHABLE while
caching the link-layer address. Future original IP packet
transmissions over the OMNI interface will use this IP to link-layer
address mapping the same as for any IPv6 interface.
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When the ARS is a Client, the SRT secured spanning tree will first
deliver the solicited NA(AR) message to the Client's FHS Proxy/
Server, which includes an OAL Extended Fragment Header with an in-
window Identification for this Client, and forwards the message to
the Client. If the Client is on a well-managed ANET, physical
security and protected spectrum ensures security for the NA(AR)
without needing an additional authentication signature or
Identification; if the Client is in a MANET or in the open INET the
Proxy/Server must instead include an Identification and
authentication signature. The Proxy/Server then includes an SRH,
changes the OAL Source Address to its own MLA and changes the OAL
Destination Address to the MLA of the next hop on the path to the
Client when it forwards the NA(AR). The Proxy/Server then decrements
the OAL Hop Limit, performs underlay encapsulation and forwards the
resulting carrier packet over the underlay interface to the Client.
When the Client receives the NA(AR), it caches the adaptation layer
information as above then removes the OMNI option and forwards the
NS(AR) to the network layer if the target is on-link. The Client is
then responsible for informing the ART if any of its adaptation layer
addressing changes (e.g., due to mobility) before the ALCNE expires.
4.13.1.6. Reliability
After the ARS transmits the first NS(AR), it should wait up to
RETRANS_TIMER seconds to receive a responsive NA(AR). The ARS can
then retransmit the NS(AR) up to MAX_UNICAST_SOLICIT times before
giving up.
4.13.2. Multilink Forwarding
Following address resolution, the ARS and ART (i.e., the end system
Clients or their respective Proxy/Servers) can assert per-flow
unidirectional multilink forwarding paths through underlay interface
pairs serviced by the same Source/Destination Addresses and Flow
Label by sending MP messages with OMNI Neighbor Synchronization sub-
options and with an OAL SRH with an AVFI option with (I)nitialize set
to 1. The MP messages establish per-flow multilink forwarding and
header compression state in OAL intermediate systems in the forward
path from the source to the target. Note that either the ARS or ART
can independently initiate multilink forwarding by sending MP
messages on behalf of specific flows over underlay interface pairs.
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The source Client or FHS Proxy/Server creates MP messages by
including OMNI option trailers for original IP packets. The source
finally performs OAL encapsulation with Source and Destination
addresses set the same as for address resolution while including an
SRH extension. The flow 3-tuple is then identified by the MP Source
Address, Destination Address and Flow Label. After sending initial
MP messages for a flow, the OAL source can begin applying header
compression for additional messages for the flow.
The multilink forwarding profile provides support for redundant paths
that each OAL node can harness to its best advantage. For example,
OAL nodes can use traffic selectors to distribute different traffic
types over available multilink paths, while other factors such as
metrics, cost, provider, etc. can also provide useful decision
points. OAL nodes can also employ multilink forwarding for fault
tolerance by sending redundant data over multiple paths
simultaneously, or for load balancing where the individual packets of
a single traffic flow are spread across multiple independent paths.
OAL nodes that engage in multilink forwarding therefore must
incorporate a policy engine that selects both inbound and outbound
multilink paths for a given traffic profile at a given point in time.
This specification therefore provides multilink forwarding mechanisms
without mandating any specific multilink policy.
All Client, Proxy/Server and Gateway nodes that configure OMNI
interfaces and engage in multilink coordination include an additional
forwarding table termed the AERO Flow Information Base (AFIB) that
supports OAL packet/fragment forwarding based on original IP packet
flows over specific OMNI neighbor interface pairs. The AFIB contains
per-flow AERO Flow Vectors (AFVs) identified by the underlay address
of the previous OAL hop plus a value known as the AFV Index (AFVI).
The AFVs cache uncompressed OAL header information to support
forwarding of packets with compressed headers as well as previous/
next-hop addressing and AFVI information. The AFVs also cache window
synchronization state (i.e., the starting sequence number and window
size) for each specific flow. Using the window synchronization
state, simple Identification-based data origin authentication is
enabled at each OAL source, intermediate system and target node.
Client and Proxy/Server OMNI interfaces manage end system AFIB
entries in conjunction with their internal ALNC, where the ALNCEs
link to (possibly) multiple AFVs with one per flow over a specific
FHS/LHS interface ifIndex pair. When OMNI interface peers need to
coordinate, they locate a NLNCE for the peer (established through
address resolution) then use the ALNCE as a nexus that aggregates
potentially many AVFs which cache AFVIs to support multilink
forwarding on a per-flow basis. Gateway OMNI interfaces and the OMNI
interfaces of Clients or Proxy/Servers acting as OAL intermediate
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nodes manage transit AFIB entries independently of their internal
neighbor caches. These transit AFVs are indexed by the underlay
address and AFVI supplied by the previous hop.
OAL source, intermediate system and target nodes create or update
AFVs/AFVIs when they process an MP message with an OMNI Neighbor
Synchronization sub-option with the SYN flag set (see:
[I-D.templin-6man-omni3]). The source of the initiating MP is
considered to reside in the "First Hop Segment (FHS)", while the
destination is considered to reside in the "Last Hop Segment (LHS)".
The FHS and LHS roles are determined on a per-flow and per-interface-
pair basis. After address resolution, either peer is equally capable
of initiating multilink forwarding on behalf of a specific flow. The
peer that sends the initiating MP message with Neighbor
Synchronization for a specific pair becomes the FHS peer while the
one that receives the MP becomes the LHS peer for that (flow,
interface pair) only. It is therefore commonplace that peers may
assume the FHS role for some flows while assuming the LHS role for
others, i.e., even though each peer maintains only a single NCE.
When an OAL node sends/forwards an MP with a Neighbor Synchronization
sub-option with the SYN flag set, it creates or updates an AFV,
caches the Identification window information, caches the OAL IPv6
header and caches the flow 3-tuple for compression/decompression of
the original IP packet header. The OAL node also records the
previous hop underlay address and AFVI, then generates a new next hop
AFVI or updates the lifetime of an already-established AFVI. The
next hop AFVI should be selected within the range [1 - (2**16-1)]
unless all values within that range are already in active use.
Otherwise, the AFVI must be selected within the range [2**16 -
(2**32-1)] while the value 0 indicates "AFVI unspecified". When the
OAL node forwards future OAL packets/fragments that include the
previous hop underlay address and AFVI, it can unambiguously locate
the correct AFV and use the cached information to forward to the next
OAL hop.
OAL nodes cache AFVs for up to ReachableTime seconds following their
initial creation. If the node processes another MP message specific
to an AFV, it updates ReachableTime to REACHABLE_TIME seconds, i.e.,
the same as for NCEs. If ReachableTime expires, the node deletes the
AFV.
The following sections provide the detailed specifications of these
MP exchanges for all nodes along the forward and reverse paths.
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4.13.2.1. FHS Client-Proxy/Server MP Forwarding
When an FHS OAL source has an original IP packet to send toward an
LHS OAL target, it first performs address resolution resulting in the
creation of an ALNCE for the MLA of the target then selects a source
and target underlay interface pair based on address resolution flow
bindings. The FHS source then uses its cached information for the
target interface as LHS information then prepares an MP message with
a Neighbor Synchronization sub-option and any necessary
authentication sub-options.
The FHS source next creates an AFV then generates and assigns an AFVI
for the flow over this interface pair; the AFVI (coupled with its UNX
address) must be unique for its communications to this next OAL hop.
The FHS source then includes an SRH with segment addressing
information and with the LHS Proxy/Server MLA as the final address.
The FHS source finally includes an OMNI Neighbor Synchronization sub-
option with window synchronization parameters and prepares the MP
message for transmission while also caching the window
synchronization parameters in the local AFV.
If the FHS source is the FHS Proxy/Server, it performs OAL
encapsulation while setting the OAL Source Address to its own MLA and
setting the OAL Destination Address to the MLA found in the target
Interface Attributes. The FHS Proxy/Server then performs underlay
encapsulation and forwards the resulting carrier packet into the
secured spanning tree which will deliver it to an FHS Gateway.
If the FHS source is the FHS Client, it instead includes an
authentication signature and OAL Extended Fragment Header with an in-
window Identification for its FHS Proxy/Server if necessary. If FMT-
Forward and FMT-Mode are both set, the Client sets the Neighbor
Synchronization LHS ifIndex to the ifIndex of the target; otherwise,
it sets the ifIndex to 0 to allow the FHS Proxy/Server to select the
target ifIndex. The FHS Client then performs OAL encapsulation while
including an SRH per [I-D.templin-6man-omni3], sets the OAL Source
Address to its own MLA and sets the OAL Destination Address to the
MLA of the first hop toward the FHS Proxy/Server. The FHS Client
finally performs underlay encapsulation and forwards the resulting
carrier packet to the FHS Proxy/Server.
If there are multiple OAL hops between the Client and FHS Proxy/
Server, the first OAL intermediate node receives the carrier packets
containing the MP then also verifies the OAL checksum and
authentication signature. The OAL intermediate node then caches the
FHS/LHS Client addressing, AFVI and window synchronization
information as previous hop information in a new or existing AFV.
The OAL intermediate hop then creates a new unique AFVI to forward to
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the next OAL hop, then both caches the AFVI and writes it into the
control message AVI field, i.e., while over-writing the value
supplied by the previous hop. The OAL intermediate node then
forwards to the next OAL hop toward the FHS Proxy/Server which then
performs the same functions as the previous OAL hop.
When the FHS Proxy/Server receives the carrier packets, it performs
underlay decapsulation, verifies the Identification, and verifies the
MP OAL checksum and authentication signature. The FHS Proxy/Server
then creates an AFV (i.e., the same as the FHS Client had done) while
caching the FHS/LHS Client addressing, AFVI and window
synchronization information as previous hop information for this AFV.
The FHS Proxy/Server next generates a new unique AFVI to forward to
the next OAL hop, then both caches the AFVI in the AFV and writes it
into the MP AFVI field. The FHS Proxy/Server next calculates the MP
OAL checksum then decrements the OAL Hop Limit, removes the OAL
Extended Fragment Header, performs underlay encapsulation and
forwards the resulting carrier packet into the secured spanning tree.
4.13.2.2. FHS/intermediate/LHS Gateway MP Forwarding
Gateways in the spanning tree forward OAL packets/fragments not
explicitly addressed to themselves, while forwarding those that
arrived via the secured spanning tree to the next hop also via the
secured spanning tree and forwarding all others via the unsecured
spanning tree. When an FHS Gateway receives an MP message over the
secured spanning tree, it performs underlay decapsulation then
verifies the MP OAL checksum. The FHS Gateway next creates an AFV
based on the previous hop Neighbor Synchronization information, i.e.,
the same as the FHS Proxy/Server had done. The FHS Gateway then
generates a locally-unique AFVI for the next hop and both caches the
value in the AFV and copies it into the MP AFVI.
The FHS Gateway then examines the SRT prefixes corresponding to both
the FHS and LHS. If the FHS Gateway has a local interface connection
to both the FHS and LHS (whether they are the same or different
segments), the FHS/LHS Gateway caches the MP Neighbor Synchronization
information in the AFV, and writes a new locally-unique AFVI for the
next hop into the AFV and MP AFVI. The FHS Gateway then decrements
the OAL Hop Limit, performs underlay encapsulation and forwards the
resulting carrier packet into the secured spanning tree.
When the FHS and LHS Gateways are different, the LHS Gateway will
receive carrier packets over the secured spanning tree from the FHS
Gateway, noting there may be many intermediate Gateways in the path
between FHS and LHS which will update their transit AFVs in the same
fashion while selecting new locally-unique AFVIs for the next hop
based on Neighbor Synchronization and SRH information. The LHS
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Gateway then performs underlay decapsulation, verifies the
Identification, verifies the MP OAL checksum then creates an AFV
(i.e., the same as all previous hop Gateways had done) while caching
the Neighbor Synchronization information from the previous hop and
creating a new AFVI for the next hop. The LHS Gateway then
decrements the OAL Hop Limit, performs underlay encapsulation and
forwards the resulting carrier packet into the secured spanning tree.
4.13.2.3. LHS Proxy/Server-Client MP Processing
When the LHS Proxy/Server receives the carrier packets from the
secured spanning tree, it performs underlay decapsulation, verifies
the MP OAL checksum then creates an AFV and caches the previous hop
Neighbor Synchronization and addressing information.
If FMT-Forward is clear and FMT-Mode is set, the LHS Proxy/Server
next resets the Neighbor Synchronization FHS ifIndex to 0. The LHS
Proxy/Server next includes an authentication signature in the MP if
necessary, changes the OAL Source Address to its own MLA, changes the
Destination Address to the MLA of the next hop toward the LHS Client
and includes an SRH with the MLAs of intermediate systems and a new
AFVI for this flow. The LHS Proxy/Server then decrements the OAL Hop
Limit, includes an OAL Extended Fragment Header with an appropriate
Identification value if necessary, performs underlay encapsulation
and forwards the resulting carrier packet to the LHS Client.
If there are multiple OAL hops between the LHS Proxy/Server and LHS
Client, the first OAL intermediate node receives the carrier packet
containing the MP then also verifies the OAL checksum and
authentication signature. The OAL intermediate node then caches the
FHS/LHS Client addressing, AFVI and window synchronization
information as previous hop information in a new or existing AFV.
The OAL intermediate hop then creates a new unique AFVI to forward to
the next OAL hop, then both caches the AFVI and writes it into the
MP's SRH, i.e., while over-writing the value supplied by the previous
hop. The OAL intermediate node then forwards to the next OAL hop
toward the LHS Client which then performs the same functions as the
previous OAL hop.
When the LHS Client receives the carrier packet, it performs underlay
decapsulation, verifies the Identification, then verifies the MP OAL
checksum/authentication signature. The LHS Client then creates an
ALNCE for the MP Source Address (if necessary) in the STALE state and
caches the MP Neighbor Synchronization information in a new AFV
associated with the NCE corresponding to the MP Source Address.
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4.13.2.4. Packet Forwarding Following MP Exchanges
Following initial MP exchanges the OAL source can begin sending
ordinary carrier packets for the flow that include OCH compressed
headers with AFVIs and Identification values within their respective
send windows without requiring security signatures and/or secured
spanning tree traversal. OAL end and intermediate systems can also
consult their AFIBs when they receive carrier packets that contain
OAL packets/fragments with AFVIs to unambiguously locate the correct
AFV and can use the AFV state to forward OAL packets/fragments to the
next hop. OAL end systems must then occasionally send additional MPs
to update window state, register new flows for optimized multilink
forwarding, confirm reachability and/or refresh AFIB cache state in
the path before ReachableTime expires.
While the OAL end systems continue to actively exchange OAL packets,
they are jointly responsible for updating cache state and per-
interface reachability before expiration. Window synchronization
state is performed on a per-flow basis and tracked in the AFVs which
are also linked to the appropriate NCE. However, the window
synchronization exchange only confirms target Client reachability
over the specific underlay interface pair. Reachability for other
underlay interfaces that share the same NCE must be determined
individually using additional MP messages that include Neighbor
Synchronization information.
OAL sources can then begin including OCHs in OAL packets/fragments
with an AFVI that OAL intermediate systems can use for shortest-path
forwarding based on AFVIs instead of spanning tree OAL IPv6
addresses. Forwarding based on the limited OCH information is
supported since all OAL nodes in the path up to (and sometimes
including) the OAL destination have already established AFVs.
When a Proxy/Server receives OAL packets/fragments destined to a
local SRT segment Client or forwards OAL packets/fragments received
from a local segment Client, it first locates the correct AFV. If
the OAL packet/fragment includes a secured control message, the
Proxy/Server uses the Client's ALNCE established through RS/RA
exchanges to re-encapsulate while sending outbound secured carrier
packets via the secured spanning tree and sending inbound secured
carrier packets while including an OAL authentication signature/
checksum. For ordinary OAL packets/fragments, the Proxy/Server uses
the same AFV if directed by AFVI and/or OAL addressing. Otherwise it
locates an AFV established through an MP exchange between the Client
and the remote SRT segment peer, and forwards the OAL packet/
fragments without first reassembling/decapsulating.
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When a source Client forwards OAL packets/fragments it can employ
header compression according to the AFVs established through an MP
exchange with a remote or local peer. When a target Client receives
carrier packets that contain OAL packets/fragments that match a local
AFV, the Client first verifies the Identification then decompresses
the headers if necessary, reassembles to obtain the OAL packet then
decapsulates and delivers the original IP packet to the network
layer.
When synchronized peer Clients in the same SRT segment with FMT-
Forward and FMT-Mode set discover each other's NATed UNX addresses,
they can exchange carrier packets that contain OAL packets/fragments
directly with header compression using AFVIs discovered as above
(see: Section 4.13.4.3).
4.13.3. Mobile Ad-hoc Network (MANET) Forwarding
Clients with OMNI interfaces configured over underlay interfaces with
indeterminant neighborhood properties may be connected to a Mobile
Ad-hoc NETwork (MANET). Each MANET may be either completely outside
of the range of any OMNI link Proxy/Servers or may require multihop
traversal between Clients acting as MANET routers to reach Proxy/
Servers that connect to the rest of the OMNI link. The former class
of MANETs must operate in isolation solely based on the unique IPv6
MLAs they configure locally. The latter class allows MANET routers
to extend infrastructure-based addressing information including MNPs
over multiple OMNI link hops as discussed in the OMNI specification.
MANET Clients configure their OMNI interfaces over one or more MANET
interfaces where multihop forwarding may be necessary. Routing
protocols suitable for use over MANET interfaces include OSPFv3
[RFC5340] with MANET Designated Router (OSPF-MDR) extensions
[RFC5614], OLSRv2 [RFC7181], Babel [RFC8966], AODVv2
[I-D.perkins-manet-aodvv2] and others. Other services specific to
MANET link-local and/or site-local operations (including SMF
[RFC6621], DLEP [RFC8175] and others) are also considered in-scope.
These services strive for optimal use of available radio bandwidth
and power consumption in their control message transmissions, but
efficient data plane operation is also essential.
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Clients must therefore reduce overhead through minimal encapsulation
and effective header compression whenever possible. For this reason,
when the MANET routing protocol discovers a new MLA-based route the
Client configures a lesser-preferred forwarding table entry over the
corresponding MANET interface and a more-preferred forwarding table
entry over the OMNI interface as specified in
[I-D.templin-6man-omni3]. This will cause the network layer to
direct outbound packets to the OMNI interface, which can apply header
compression and underlay MANET interface selection.
Multilink Clients that connect a MANET to the rest of the OMNI link
act as regular Clients for exchanges with external INETs, but act as
Proxy/Servers over their MANET interfaces. Each such Client
therefore has at least two underlay interfaces, including both INET
and MANET interfaces. The Client therefore services the MANET as if
it were a Proxy/Server but presents itself as a Client to external
facing INETs. This class of Clients are also known as "Proxy/
Clients".
The process for a multihop Client to establish multilink forwarding
and header compression AFV state in the MANET is conducted in the
same fashion as described above and using the same MP message
exchanges. Each MANET forwarding node in the path creates or updates
AFV state in the same fashion as for intermediate Gateways in the
secured spanning tree except that MP messages require authentication
signatures (unless neighboring MANET nodes apply lower-layer
security) and an Identification that is within the window for its
serving Proxy/Server if the destination is outside of the local MANET
cluster. The MP messages extend from the initiating FHS MANET
Client, then across any MANET hops over intermediate FHS Proxy/
Clients, then to the FHS Proxy/Server, then across the secured SRT
spanning tree to the LHS Proxy/Server, then finally across any
intermediate LHS MANET hops to the responding LHS Client. (When the
source and target Client are both within the same local MANET
cluster, however, the process is conducted directly between the two
Clients without engaging the FHS Proxy/Server.) In all other ways,
the MP message exchanges are the same as discussed in Section 4.13.2.
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Following the MP message exchanges, each MANET router in the forward
(and optionally also reverse) path in both the FHS and LHS MANETs
will have established AFVs containing multilink forwarding and header
compression state for the flow. The AFVs determine AFVI-based
forwarding based on the OCH header contents, and each MANET router
only forwards packets with in-window Identification values for the
flow. MANET routers maintain AFVs for up to ReachableTime seconds
unless they are refreshed by a new MP message. New window
synchronization exchanges must also be performed periodically to
avoid window exhaustion and/or spoofing based on predictable
Identifications.
Note: while the MANET routing protocol runs directly over the node's
MANET interfaces to discover routing information, the node configures
lesser-preferred forwarding table entries over the MANET interface
and corresponding more-preferred forwarding table entries over the
OMNI interface. This causes the network layer to forward outbound
packets via the OMNI interface which applies encapsulation,
fragmentation and/or header compression as necessary before
forwarding over the underlying MANET interface. The OMNI protocol
designator in the UDP port, IP protocol or Ethernet EtherType field
will then cause the packets to visit the OMNI interface of each
successive next-hop MANET node.
4.13.4. AERO Route Optimization
4.13.4.1. Proxy/Server-to-Proxy/Server Route Optimization
When the FHS and LHS Proxy/Servers are both connected to an IPv6
underlay for the same SRT segment, they can forward MP message
exchanges directly over the underlay without engaging SRT spanning
tree hops.
If the underlay is not secured, the FHS and LHS Proxy/Servers must
include an authentication signature with their MP messages, which
could either be the original authentication signature included by
their respective Clients or a new signature included by the Proxy/
Server itself. If the Proxy/Server that processes the MP message
determines that the message is authentic, it creates or updates an
AFV entry according to the multilink forwarding parameters. This
establishes both AFVI and Identification window state to be used for
future data traffic forwarding.
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4.13.4.2. Gateway-to-Proxy/Server Route Optimization
When the LHS gateway and FHS Proxy/Server are both connected to an
IPv6 underlay for the same SRT segment, they can forward MP message
exchanges directly over the underlay without engaging additional SRT
spanning tree hops. In this arrangement, the LHS Gateway acts the
same as the FHS Proxy/Server as discussed in Section 4.13.4.1 and
observes the requirement for including authentication signatures.
4.13.4.3. Client-to-Client Route Optimization
When the FHS/LHS Clients are both located on the same SRT segment,
Client-to-Client route optimization is possible following the
establishment of any necessary state in NATs in the path. Both
Clients will have already established state via their respective
shared segment Proxy/Servers (and possibly also any shared segment
Gateways) and can begin sending carrier packets directly via NAT
traversal while avoiding any Proxy/Server and/or Gateway hops.
When the FHS/LHS Clients on the same SRT segment perform initial MP
message exchanges to establish AFIB state, they first examine the
FMT-Forward and FMT-Mode settings to determine whether direct-path
forwarding is even possible for one or both Clients (direct-path
forwarding is only possible when FMT-Forward and FMT-Mode are both
set). The MP messages then include an Interface Attributes sub-
option (i.e., in addition to a Neighbor Synchronization sub-option)
with the mapped UNX information discovered during the RS/RA exchanges
with their respective Proxy/Servers. After the AFV paths have been
established, both Clients can begin sending carrier packets via
strict AFV paths while establishing a direct path for Client-to-
Client route optimization.
To establish the direct path, either Client (acting as the source)
transmits a bubble to the mapped UNX for the target Client which
primes the local chain of NATs for reception of future carrier
packets from that UNX (see: [RFC4380] and [I-D.templin-6man-omni3]).
The source Client then prepares an MP message with the FNP/MNP
address of a subject packet as the Source Address, with the FNP/MNP
address of the target as the Target and Destination Address and with
an OMNI option with an Interface Attributes sub-option. The source
Client then encapsulates the MP in an OAL header and SRH extension
with its own MLA as the Source Address, with the MLA of the next OAL
hop toward the Proxy/Server as the Destination Address and with an
in-window Identification for the target. The source Client then
performs underlay encapsulation and sends the resulting carrier
packets to the Proxy/Server which re-encapsulates and sends them as
unsecured carrier packets according to AFIB state where they will
eventually arrive at the target Client.
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Following initial MP message exchanges, both Clients mark their
respective (source, target) underlay interface pairs as "trusted" for
no more than ReachableTime seconds. The Clients can then begin
exchanging ordinary data packets as OCH encapsulated carrier packets.
While the Clients continue to exchange packets via the direct path
avoiding all Proxy/Servers and Gateways, they should perform
additional MP message exchanges via their local Proxy/Servers to
refresh NCE state as well as send additional bubbles to the peer's
UNX if necessary to refresh NAT state.
Note: these procedures apply for a widely-deployed but basic class of
NATs. Procedures for advanced NAT classes are outlined in [RFC6081],
which provides mechanisms that can be employed equally for AERO using
the corresponding sub-options specified by OMNI.
Note: each communicating pair of Clients may need to maintain NAT
state for peer to peer communications via multiple underlay interface
pairs and/or multiple flows. It is therefore important that UNX
information is maintained with the correct peer interface and that
the NCE may cache information for multiple peer interfaces.
Note: the source and target Client exchange UNX information during
the secured MP multilink route optimization exchange. This allows
for subsequent MP exchanges to proceed using only the Identification
value as a data origin confirmation. However, Client-to-Client
peerings that require stronger security may also include
authentication signatures for mutual authentication.
4.13.4.4. Intra-(M)ANET/EUN Route Optimization
When a Client forwards an OAL packet (or an original IP packet) from
another Client connected to one of its downstream EUNs to a peer
within the same downstream EUN, the Client returns an IPv6 ND
Redirect message to inform the source that the target can be reached
directly. The contents of the Redirect message are the same as
specified in [RFC4861] except that the message includes MLAs instead
of LLAs, and should also include any OMNI option RIOs with MNP
information corresponding to the target.
In the same fashion, when a Proxy/Server forwards an OAL packet (or
original IP packet) from a Client connected to one of its downstream
*NETs to a peer within the same downstream *NET, the Proxy/Server
returns an IPv6 ND Redirect message.
All other route optimization functions are conducted per the MP
messaging discussed in the previous sections.
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4.14. Neighbor Unreachability Detection (NUD)
AERO nodes perform Neighbor Unreachability Detection (NUD) per
[RFC4861] either reactively in response to persistent link layer
errors (see: Section 4.11) or proactively to confirm reachability.
The NUD algorithm is based on periodic control message exchanges and
may further be seeded by IPv6 ND hints of forward progress, but care
must be taken to avoid inferring reachability based on spoofed
information.
For on-link destinations, NUD messaging is driven by the network
layer under the same conditions as for any interface; for off-link
destinations, the process is driven by the adaptation layer. The NS/
NA(NUD) messages follow the same forwarding and processing rules as
for address resolution and confirm that the target neighbor is still
reachable over a selected underlay interface path. The messages may
also update NLNCE/ALNCE state if they include address resolution
information and an authentication signature.
In order to test additional underlay interface paths, the adaptation
layer can independently send an NS(NUD) message with an SRH with an
AFVI with the (I)nitialize flag set to 0 in order to receive an
NA(NUD) response. The NS messages may be sent while ordinary data
packets are flowing to follow already-established paths without
updating state and therefore need not include an authentication
signature but should include an OMNI Nonce sub-option.
When the source receives the NA, it marks the target underlay
interface tested as "trusted". Note that underlay interface states
are maintained independently of the overall NCE REACHABLE state, and
that a single NCE may have multiple target underlay interfaces in
various "trusted/untrusted" states while the NCE state as a whole
remains REACHABLE.
4.15. Mobility Management and Quality of Service (QoS)
AERO is a fully Distributed Mobility Management (DMM) service in
which each Proxy/Server is responsible for only a subset of the
Clients on the OMNI link. This is in contrast to a Centralized
Mobility Management (CMM) service where there are only one or a few
network mobility collective entities for large Client populations.
Clients coordinate with their associated FHS and MAP Proxy/Servers
via RS/RA exchanges to maintain the DMM profile, and the AERO routing
system tracks all current Client/Proxy/Server peering relationships.
MAP Proxy/Servers provide an address resolution aggregation point for
their dependent Clients, while FHS Proxy/Servers provide a proxy
conduit between the Client and both the MAP and OMNI link in general.
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Clients are responsible for maintaining neighbor relationships with
their Proxy/Servers through periodic RS/RA exchanges, which also
serve to confirm neighbor reachability. When a Client's underlay
interface attributes change, the Client is responsible for updating
the MAP Proxy/Server through new RS/RA exchanges using the FHS Proxy/
Server as a first-hop conduit. The FHS Proxy/Server can also act as
a proxy to perform some IPv6 ND exchanges on the Client's behalf
without consuming bandwidth on the Client underlay interface.
Note: when a Client's underlay interface address changes, the Client
and/or its (former) FHS Proxy/Server for this interface must
invalidate any AFVs based on the (changed) interface. Future data
packet forwarding will then trigger a new multilink forwarding MP
message exchange to re-populate new AFVs in the path.
Mobility management considerations are specified in the following
sections.
4.15.1. Registering Link-Layer Information Changes
When a Client needs to change its underlay Interface Attributes and/
or Traffic Selectors for one or more underlay interfaces (e.g., due
to a mobility event), it sends RS messages to its MAP Proxy/Server
via new FHS Proxy/Servers if necessary. Each RS includes an OMNI
option with Interface Attributes and/or Traffic Selector sub-options
for the ifIndex in question.
Note that the FHS Proxy/Server may change due to an underlay
interface connectivity change or an intentional switch to a new
Proxy/Server. If the Client RS includes an OMNI Proxy/Server
Departure sub-option for the former FHS Proxy/Server, the new FHS
Proxy/Server can send a departure indication (see: Section 4.15.3);
otherwise, any stale state in the former FHS Proxy/Server will simply
expire after ReachableTime expires with no effect on the MAP Proxy/
Server.
Up to MAX_RTR_SOLICITATIONS RS messages MAY be sent in parallel with
sending carrier packets containing user data in case one or more RAs
are lost. If all RAs are lost, the Client SHOULD re-associate with a
new Proxy/Server.
When a Client needs to bring new underlay interfaces into service
(e.g., when it activates a new data link), it sends an RS message to
the MAP Proxy/Server via a FHS Proxy/Server for the underlay
interface (if necessary) with an OMNI option that includes an
Interface Attributes sub-option with interface parameters and with
address resolution information for the new link.
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4.15.2. Deactivating Existing Links
When a Client needs to deactivate an existing underlay interface, it
sends an RS message toward the MAP Proxy/Server via an FHS Proxy/
Server with an OMNI option with appropriate Interface Attributes
values for the deactivated link.
If the Client needs to send RS messages over an underlay interface
other than the one being deactivated, it MUST include current
Interface Attributes for the link used as the first sub-option as
well as additional Interface Attributes for any underlay interfaces
being deactivated as additional sub-options with ifMetric set to
'ffffffff'. The Client (or its MAP Proxy/Server) then again sends
uNA messages to all neighbors the same as described above.
Note that when a Client deactivates an underlay interface, neighbors
that receive the ensuing uNA messages need not purge all references
for the underlay interface from their NCEs. The Client may
reactivate or reuse the underlay interface and/or its ifIndex at a
later point in time, when it will send new RS messages to an FHS
Proxy/Server with fresh interface parameters to update any neighbors.
The manner in which the Client dynamically manages its local ifIndex
to interface mappings is a local decision, but should not be done in
a manner that could cause state inconsistencies in the network.
4.15.3. Moving Between Proxy/Servers
When a Client associates with a new MAP Proxy/Server, it sends RS
messages to register its underlay interfaces with the new MAP while
including the departed MAP's MLA in a Proxy/Server Control OMNI sub-
option. When the new MAP Proxy/Server returns an RA message via the
FHS Proxy/Server (acting as a proxy), the FHS Proxy/Server sends a
uNA to the departed MAP Proxy/Server if the departed MLA is other
than ::/128. Note that the FHS Proxy/Server defers the uNA
transmission until after the new MAP has responded for reliability
purposes; if even greater reliability is needed, the FHS Proxy/Server
can instead send an NS(NUD) message to receive an NA(NUD) response.
The FHS Proxy/Server sets the uNA Source Address to the MLA of the
new MAP, sets the Target Address to the Client's MLA and sets the
Destination Address to the MLA of the departed MAP. The FHS Proxy/
Server then includes a Proxy/Server Control OMNI sub-option with the
M flag set to 1 and all other flags set to 0 and with no departed
addresses included. The FHS Proxy/Server then encapsulates the uNA
in an OAL header with its own MLA as the Source Address and the MLA
of the departed MAP as the Destination Address, then performs
underlay encapsulation and forwards the resulting carrier packet via
the secured spanning tree.
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When the departed MAP Proxy/Server receives the carrier packet, it
decapsulates to obtain the uNA and examines the Proxy/Server Control
sub-option M flag. If the M flag is 1 the departed MAP Proxy/Server
then changes the Client's NCE state to DEPARTED, resets DepartTime
and caches the new MAP Proxy/Server MLA. After a short delay (e.g.,
2 seconds) the departed MAP Proxy/Server withdraws the Client's
MNP(s) from the routing system. While in the DEPARTED state, the
departed MAP Proxy/Server forwards any carrier packets received via
the secured spanning tree destined to the Client's MNP addresses to
the new MAP Proxy/Server's MLA. When DepartTime expires, the
departed MAP Proxy/Server deletes the Client's NCE.
Mobility events may also cause a Client to change to a new FHS Proxy/
Server over a specific underlay interface at any time such that a
Client RS/RA exchange over the underlay interface will engage the new
FHS Proxy/Server instead of the old. The Client can arrange to
inform the old FHS Proxy/Server of the departure by including a
Proxy/Server Control sub-option with the MLA of the departed FHS
Proxy/Server. The new FHS Proxy/Server will issue a uNA (or NS/NA)
using the same procedures as outlined for the MAP above.
The new FHS Proxy/Server sets the uNA Source Address its own MLA,
sets the Target Address to the Client's MLA and sets the Destination
Address to the MLA of the departed FHS Proxy/Server. The new FHS
Proxy/Server then includes a Proxy/Server Control OMNI sub-option
with the P flag set to 1 and all other flags set to 0 and with no
departed addresses included. The new FHS Proxy/Server then
encapsulates the uNA in an OAL header with its own MLA as the Source
Address and the MLA of the old FHS Proxy/Server as the Destination
Address, then performs underlay encapsulation and forwards the
resulting carrier packet via the secured spanning tree.
When the departed FHS Proxy/Server receives the uNA, it updates the
Client's MLA to the address of the new FHS Proxy/Server and sets the
NCE state to DEPARTED. The departed FHS Proxy/Server can then
forward any packets it receives for the Client to its new FHS Proxy/
Server. The departed FHS Proxy/Server's NCE for the Client will then
naturally expire if no further RS message arrive. This can often
result in successful delivery of carrier packets that would otherwise
be lost temporarily due to the mobility event.
Clients SHOULD NOT move rapidly between MAP Proxy/Servers in order to
avoid causing excessive oscillations in the AERO routing system.
Examples of when a Client might wish to change to a different MAP
Proxy/Server include a MAP Proxy/Server that has become unresponsive,
topological movements of significant distance, movement to a new
geographic region, movement to a new OMNI link segment, etc.
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Note that a Client simultaneous change to both a new FHS and MAP
Proxy/Server is signaled by the new FHS when it sends a uNA to both
the departed FHS and MAP Proxy/Server. If both the departed FHS/MAP
are one and the same, and the new FHS/MAP are one and the same, the
new FHS sends a single uNA (or NS/NA) with both the M and P flags set
to 1, i.e., it need not send multiple messages.
4.15.4. Mobility Update Messaging
Mobile Clients (and/or their MAP Proxy/Servers) accommodate mobility
and/or multilink change events by sending secured uNA messages to
each neighbor that previously received address resolution
information. When a node sends a uNA message to each specific
neighbor on behalf of a mobile Client, it sets the IPv6 Source and
Target Address to the Client's MLA then sets the Destination Address
to the neighbor's MLA.
The node then encapsulates the uNA in an OAL header with Source set
to its own MLA and Destination set to the MLA of the neighbor. The
node also includes an OMNI option with Interface Attributes and
Traffic Selector sub-options for any of the mobile Client's underlay
interfaces that may have changed values and includes an
authentication signature if necessary.
The node next sets the uNA R flag to 1, S flag to 0 and O flag to 1,
then encapsulates the message in an OAL header. Following OAL and
underlay encapsulation, the carrier packet containing the uNA message
will then follow the secured spanning tree and arrive at the specific
neighbor.
As discussed in Section 7.2.6 of [RFC4861], the transmission and
reception of uNA messages is unreliable but provides a useful
optimization. In well-connected Internetworks with robust data links
uNA messages will be delivered with high reliability, but in any case
the node can optionally send up to MAX_NEIGHBOR_ADVERTISEMENT uNAs to
each neighbor to increase the likelihood that at least one will be
received. Alternatively, the node can send an NS(MM) message to
solicit an NA(MM) response as discussed in Section 4.5.1.
When the neighbor receives a uNA with address resolution changes, it
marks any AFVs in its ALNCE for the uNA source that were established
based on now-obsolete information as STALE. When the neighbor
forwards the next packet for an affected flow, it initiates a new
multilink forwarding exchange as specified in Section 4.13.2 to
refresh AFVI state for the path.
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4.15.5. Accommodating Path Changes
After AFV state has been established for a flow, all OAL intermediate
systems in the forward path will have AFVs with header compression
state and (AFVI, UNX) information for the next hop. However, paths
can fluctuate due to factors such as node mobility, routing changes,
network membership, etc. If an OAL intermediate system forwarding
OAL packets with OCH headers detects that the next hop in the path
has changed, it immediately reverts to sending the packets with
header compression disabled by including full OAL IPv6 and Extended
Fragment Headers (plus full original IP headers) in future packets.
When the OAL destination begins to receive OAL packets with full
headers (i.e., when it had previously received authentic MP messages
for this flow), it assumes that the network path has changed and
begins returning uNA messages to the OAL source. The OAL destination
sends the uNA messages subject to rate limiting, and includes an
ICMPv6 Error message OMNI sub-option with Type 4 ("Parameter
Problem"), with Code TBD ("Compressed header expected" - see IANA
Considerations) and with at least the full uncompressed original IP
packet header in the packet-in-error field. The OAL destination then
delivers the packet to upper layers.
When the OAL source receives the uNA messages, it refreshes multilink
forwarding state for this flow by issuing new MP messages the same as
for a new flow as specified in Section 4.13.2. OAL intermediate
nodes in the former path will then simply purge the stale AFV state
when it expires. The OAL source does not report an error to upper
layers as the OAL destination has already accepted the packet.
4.16. Multicast
Each Client provides an IGMP (IPv4) [RFC2236] or MLD (IPv6) [RFC3810]
proxy service for its EUNs and/or hosted applications [RFC4605] and
acts as a Protocol Independent Multicast - Sparse-Mode (PIM-SM, or
simply "PIM") Designated Router (DR) [RFC7761] on the OMNI link.
Proxy/Servers act as OMNI link PIM routers for Clients on ANET, VPN/
IPsec or Direct interfaces, and Relays also act as OMNI link PIM
routers on behalf of nodes on other links/networks.
Clients on VPN/IPsec, Direct or (M)ANET underlay interfaces for which
the *NET has deployed native multicast services forward IGMP/MLD
messages into the *NET. The IGMP/MLD messages may be further
forwarded by a first-hop *NET access router acting as an IGMP/MLD-
snooping switch [RFC4541], then ultimately delivered to a *NET (FHS)
Proxy/Server. The FHS Proxy/Server then acts as an ARS to send
NS(AR) messages to an ARR for the multicast source. Clients on *NET
underlay interfaces without native multicast services instead send
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NS(AR) messages as an ARS to cause their FHS Proxy/Server to forward
the message to an ARR. When the ARR prepares an NA(AR) response, it
initiates PIM protocol messaging according to the Source-Specific
Multicast (SSM) and Any-Source Multicast (ASM) operational modes as
discussed in the following sections.
4.16.1. Source-Specific Multicast (SSM)
When an ARS "X" (i.e., either a Client or Proxy/Server) acting as PIM
router receives a Join/Prune message from a node on its downstream
interfaces containing one or more ((S)ource, (G)roup) pairs, it
updates its Multicast Routing Information Base (MRIB) accordingly.
For each S belonging to a prefix reachable via X's non-OMNI
interfaces, X then forwards the (S, G) Join/Prune to any PIM routers
on those interfaces per [RFC7761]. The same as for unicast
destinations, the 3-tuple of Source Address, Destination Address and
Flow Label identifies a flow for multicast group G.
For each S belonging to a prefix reachable via X's OMNI interface, X
sends an NS(AR) message (see: Section 4.13) into the secured spanning
tree which delivers it to ARR "Y" that services S. Y will then
return an NA(AR) that includes an OMNI option with Interface
Attributes, Traffic Selectors and RIOs for S.
When X processes the NA(AR) it selects one or more underlay
interfaces for S and performs an MP multilink forwarding message
exchange over the secured spanning tree while including a PIM Join/
Prune message OMNI sub-option for each multicast group of interest.
If S is located behind any Proxys "Z"*, each Z* then updates its MRIB
accordingly and maintains the FNP/MNP Source Address of X as the next
hop in the reverse path. Since Gateways forward messages not
addressed to themselves without examining them, this means that the
(reverse) multicast tree path is simply from each Z* (and/or S) to X
with no other multicast-aware routers in the path.
Following the initial combined Join/Prune and MP messaging, X
maintains a NCE for each S the same as if X was sending unicast data
traffic to S. In particular, X performs additional MP message
exchanges to keep the NCE alive for up to t_periodic seconds
[RFC7761]. If no new Joins are received within t_periodic seconds, X
allows the NCE to expire. Finally, if X receives any additional
Join/Prune messages for (S,G) it forwards the messages over the
secured spanning tree.
Client C that holds an MNP for source S may later depart from a first
Proxy/Server Z1 and/or connect via a new Proxy/Server Z2. In that
case, Y sends an MP message to X the same as specified for unicast
mobility in Section 4.15. When X receives the MP message, it updates
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its NCE for the MLA for source S and sends new Join messages in MP
message exchanges addressed to the new target Client underlay
interface connection for S. There is no requirement to send any
Prune messages to old Proxy/Server Z1 since source S will no longer
source any multicast data traffic via Z1. Instead, the multicast
state for (S,G) in Proxy/Server Z1 will soon expire since no new
Joins will arrive.
4.16.2. Any-Source Multicast (ASM)
When an ARS "X" acting as a PIM router receives Join/Prune messages
from a node on its downstream interfaces containing one or more (*,G)
pairs, it updates its Multicast Routing Information Base (MRIB)
accordingly. X first performs an NS/NA(AR) exchange to receive
address resolution information for Rendezvous Point (RP) "R" for each
G. X then includes a copy of each Join/Prune message in the OMNI
option of an MP message, then encapsulates the MP message in an OAL
header and sends the message into the secured spanning tree.
For each source "S" that sends multicast traffic to group G via R,
Client S* that aggregates S (or its Proxy/Server) encapsulates the
original IP packets in PIM Register messages, includes the PIM
Register messages in the OMNI options of MP messages, performs OAL
encapsulation and fragmentation with Identification values within the
receive window for Client R* that aggregates R, then performs
underlay encapsulation and forwards the resulting carrier packets.
Client R* may then elect to send a PIM Join to S* in the OMNI option
of a MP over the secured spanning tree. This will result in an (S,G)
tree rooted at S* with R as the next hop so that R will begin to
receive two copies of the original IP packet; one native copy from
the (S, G) tree and a second copy from the pre-existing (*, G) tree
that still uses MP PIM Register encapsulation. R can then issue an
MP with a PIM Register-stop message over the secured spanning tree to
suppress the Register-encapsulated stream. At some later time, if
Client S* moves to a new Proxy/Server, it resumes sending original IP
packets via MP PIM Register encapsulation via the new Proxy/Server.
At the same time, as multicast listeners discover individual S's for
a given G, they can initiate an (S,G) Join for each S under the same
procedures discussed in Section 4.16.1. Once the (S,G) tree is
established, the listeners can send (S, G) Prune messages to R so
that multicast original IP packets for group G sourced by S will only
be delivered via the (S, G) tree and not from the (*, G) tree rooted
at R. All mobility considerations discussed for SSM apply.
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4.16.3. Bi-Directional PIM (BIDIR-PIM)
Bi-Directional PIM (BIDIR-PIM) [RFC5015] provides an alternate
approach to ASM that treats the Rendezvous Point (RP) as a Designated
Forwarder (DF). Further considerations for BIDIR-PIM are out of
scope.
4.17. Operation over Multiple OMNI Links
An AERO Client can connect to multiple OMNI links the same as for any
data link service. In that case, the Client maintains a distinct
OMNI interface for each link, e.g., 'omni0' for the first link,
'omni1' for the second, 'omni2' for the third, etc. Each OMNI link
would include its own distinct set of Gateways and Proxy/Servers,
thereby providing redundancy in case of failures.
Each OMNI link could utilize the same or different ANET/INET link
layer connections. The links can be distinguished at the link layer
via the SRT prefix in a similar fashion as for Virtual Local Area
Network (VLAN) tagging (e.g., IEEE 802.1Q) and/or through assignment
of distinct sets of MSPs on each link. This gives rise to the
opportunity for supporting multiple redundant networked paths (see:
Section 4.2.4).
The Client's network layer can select the outbound OMNI interface
appropriate for a given traffic profile while (in the reverse
direction) correspondent nodes must have some way of steering their
original IP packets destined to a target via the correct OMNI link.
In a first alternative, if each OMNI link services different MSPs the
Client can receive a distinct MNP from each of the links. IP routing
will therefore assure that the correct OMNI link is used for both
outbound and inbound traffic. This can be accomplished using
existing technologies and approaches, and without requiring any
special supporting code in correspondent nodes or Gateways.
In a second alternative, if each OMNI link services the same MSP(s)
then each link could assign a distinct "OMNI link Anycast" address
that is configured by all Gateways on the link. Correspondent nodes
can then perform Segment Routing to select the correct SRT, which
will then direct the original IP packet over multiple hops to the
target.
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4.18. Transition/Coexistence Considerations
OAL encapsulation ensures that dissimilar INET partitions can be
joined into a single unified OMNI link, even though the partitions
themselves may have differing protocol versions and/or incompatible
addressing plans. However, a commonality can be achieved by
incrementally distributing globally routable (i.e., native) IP
prefixes to eventually reach all nodes (both mobile and fixed) in all
OMNI link segments. This can be accomplished by incrementally
deploying AERO Gateways on each INET partition, with each Gateway
distributing its MNPs and/or discovering FNPs on its INET links.
This gives rise to the opportunity to eventually distribute native IP
addresses to all nodes, and to present a unified OMNI link view even
if the INET partitions remain in their current protocol and
addressing plans. In that way, the OMNI link can serve the dual
purpose of providing a mobility/multilink service and a transition/
coexistence service. Alternatively, if an INET partition is
transitioned to a native IP protocol version and addressing scheme
compatible with the OMNI link MNP-based addressing scheme, the
partition and OMNI link can be joined by Gateways.
Relays that connect INETs/EUNs with dissimilar IP protocol versions
may need to employ a network address and protocol translation
function such as NAT64 [RFC6146].
4.19. Proxy/Server-Gateway Bidirectional Forwarding Detection
In environments where rapid failure recovery is essential, Proxy/
Servers and Gateways SHOULD use Bidirectional Forwarding Detection
(BFD) [RFC5880]. Nodes that use BFD can quickly detect and react to
failures so that cached information is re-established through
alternate nodes. BFD control messaging is carried only over well-
connected ground domain networks (i.e., and not low-end radio links)
and can therefore be tuned for rapid response.
Proxy/Servers and Gateways can maintain BFD sessions in parallel with
their BGP peerings. If a Proxy/Server or Gateway fails, BGP peers
will quickly re-establish routes through alternate paths the same as
for common BGP operational practice.
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4.20. Time-Varying MNPs
In some use cases, it is desirable, beneficial and efficient for the
Client to receive a constant MNP that travels with the Client
wherever it moves. For example, this would allow air traffic
controllers to easily track aircraft, etc. In other cases, however
(e.g., intelligent transportation systems), the MN may be willing to
sacrifice a modicum of efficiency in order to have time-varying MNPs
that can be changed every so often to defeat adversarial tracking.
The DHCPv6 service offers a way for Clients that desire time-varying
MNPs to obtain short-lived prefixes (e.g., on the order of a small
number of minutes). In that case, the identity of the Client would
not be bound to the MNP but rather to a Node Identification value
(see: [I-D.templin-6man-omni3]) that can serve as a Client ID seed
for MNP prefix delegation. The Client would then be obligated to
renumber its internal networks whenever its MNP changes. This should
not present problems for Clients with automated network renumbering
services, however it can limit the durations of ongoing sessions that
would prefer to use a constant address.
5. Implementation Status
AERO/OMNI Release-3.2 was tagged on March 30, 2021, and was subject
to internal testing. The implementation is not planned for public
release.
A write-from-scratch reference implementation is under active
internal development, with release version v0.pre8 tagged on January
16, 2026. Future versions will be made available for public release.
6. IANA Considerations
The IANA is requested to assign a new Code TBD ("Compressed header
expected") in the "ICMPv6 Parameter Problem" registry
[https://www.iana.org/assignments/icmpv6-parameters/
icmpv6-parameters.xhtml]. Registration Procedures include Standards
Action or IESG Approval.
The IANA assigned UDP port number "8060" for an experimental first
edition of AERO [RFC6706]. The Overlay Multilink Network Interface
(OMNI) specification [I-D.templin-6man-omni3] reclaims "8060" as the
service port for AERO/OMNI UDP/IP encapsulation, therefore this
document makes no IANA request. (Note: although [RFC6706] was not
widely implemented or deployed, it need not be obsoleted since it
uses ICMPv6 message type '0' (Reserved) which implementations of this
specification ignore.)
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7. Security Considerations
AERO Gateways establish security associations with AERO Proxy/Servers
and Relays within their local OMNI link segments using secured
tunnels over underlay interfaces. The AERO Gateways of all OMNI link
segments in turn configure secured tunnels with neighboring AERO
Gateways for other OMNI link segments in a secured spanning tree
topology. Applicable security services include IPsec [RFC4301] with
IKEv2 [RFC7296], etc. (Note that secured direct point-to-point links
can also be used instead of or in addition to network layer
security.) Together, these services are responsible for assuring
connectionless integrity and data origin authentication with optional
protection against replays for control messages that traverse the
secured spanning tree.
To prevent unauthorized local applications from congesting the
secured spanning tree, Proxy/Servers and Gateways configure local
access controls to permit only the BGP protocol service daemon to
source routing protocol control messages with the MLA assigned to the
OMNI interface as the source over the secured spanning tree. An
implementation can employ a port/address filtering configuration that
permits only TCP port 179 (as defined in the IANA "Service Names and
Port Numbers" registry) when using the MLA assigned to the OMNI
interface. To prevent malicious Clients from congesting the secured
spanning tree, Proxy/Servers should also rate-limit the secured IPv6
ND messages they process for the same (source, target) pair, e.g., by
applying IPv6 ND MAX_UNICAST_SOLICIT; MAX_NEIGHBOR_ADVERTISEMENT
limits.
To prevent spoofing, Proxy/Servers MUST silently discard without
responding to any unsecured IPv6 ND messages with OMNI sub-options
that would otherwise affect state. Also, Proxy/Servers MUST silently
discard without forwarding any original IP packets received from one
of their own Clients (whether directly or following OAL reassembly)
with a Source Address that does not match the Client's MNP and/or a
Destination Address that does match the Client's MNP. Finally,
Proxy/Servers MUST silently discard without forwarding any carrier
packets that include an OAL packet/fragment with Source and
Destination Addresses that both match the same MNP.
AERO Clients that connect to secured ANETs need not apply additional
security to their IPv6 ND messages, since the messages will be
accepted and forwarded by a perimeter Proxy/Server that applies
security over its INET-facing interface to the secured spanning tree
(see above). AERO Clients that connect to MANETs or open INETs can
use network and/or transport layer security services such as VPNs
(e.g., IPsec tunnels) or can by some other means establish a secured
direct link to a Proxy/Server. When a VPN or direct link may be
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impractical, however, INET Clients and Proxy/Servers SHOULD include
and verify authentication signatures for IPv6 ND messages as
specified in [I-D.templin-6man-omni3].
End systems SHOULD apply transport or higher layer security services
such as QUIC-TLS [RFC9000], TLS/SSL [RFC8446], DTLS [RFC6347], etc.
to provide a level of protection comparable to critical secured
Internet services. End systems that require host-based VPN services
SHOULD use network and/or transport layer security services such as
IPsec, TLS/SSL, DTLS, etc. AERO Proxy/Servers and Clients can also
provide a network-based VPN service on behalf of end systems, e.g.,
if the end system is located within a secured enclave and cannot
establish a VPN on its own behalf.
AERO Proxy/Servers and Gateways present targets for traffic
amplification Denial of Service (DoS) attacks. This concern is no
different than for widely-deployed VPN security gateways in the
Internet, where attackers could send spoofed packets to the gateways
at high data rates. This can be mitigated through the AERO/OMNI data
origin authentication procedures, as well as connecting Proxy/Servers
and Gateways over dedicated links with no connections to the Internet
and/or when connections to the Internet are only permitted through
well-managed firewalls. Traffic amplification DoS attacks can also
target an AERO Client's low data rate links. This is a concern not
only for Clients located on the open Internet but also for Clients in
secured enclaves. AERO Proxy/Servers and Proxys can institute rate
limits that protect Clients from receiving carrier packet floods that
could DoS low data rate links.
AERO Relays must implement ingress filtering to avoid a spoofing
attack in which spurious messages with ULA addresses are injected
into an OMNI link from an outside attacker. AERO Clients MUST ensure
that their connectivity is not used by unauthorized nodes on their
EUNs to gain access to a protected network, i.e., AERO Clients that
act as routers MUST NOT provide routing services for unauthorized
nodes. (This concern is no different than for ordinary hosts that
receive an IP address delegation but then "share" the address with
other nodes via some form of Internet connection sharing such as
tethering.)
The AERO service for MANET and open INET Clients depends on a public
key distribution service in which Client public keys and identities
are maintained in a shared database accessible to Proxy/Servers and
potential correspondent peer nodes. Similarly, each Client must be
able to determine the public key of each Proxy/Server, e.g. by
consulting an online database.
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The PRL contains only public information, but MUST be well-managed
and secured from unauthorized tampering. The PRL can be conveyed to
the Client in a similar fashion as in [RFC5214] (e.g., through data
link layer login messaging, secure upload of a static file, DNS
lookups, etc.).
Security considerations for IPv6 fragmentation and reassembly are
discussed in [I-D.templin-6man-omni3]. In environments where
spoofing is considered a threat, all OAL nodes SHOULD employ
Identification window synchronization and OAL end systems SHOULD
configure an (end-system-based) firewall.
Security considerations for accepting link layer ICMP messages and
reflected carrier packets are discussed throughout the document.
8. Acknowledgements
Discussions in the IETF, aviation standards communities and private
exchanges helped shape some of the concepts in this work.
Individuals who contributed insights include Mikael Abrahamsson,
Felipe Magno de Almeida, Mark Andrews, Fred Baker, Amanda Baber, Bob
Braden, Stewart Bryant, Scott Burleigh, Brian Carpenter, Wojciech
Dec, Pavel Drasil, Ralph Droms, Adrian Farrel, Nick Green, Sri
Gundavelli, Brian Haberman, Bernhard Haindl, Joel Halpern, Tom
Herbert, Bob Hinden, Sascha Hlusiak, Lee Howard, Christian Huitema,
Zdenek Jaron, Andre Kostur, Hubert Kuenig, Eliot Lear, Ted Lemon,
Andy Malis, Satoru Matsushima, Tomek Mrugalski, Thomas Narten, Madhu
Niraula, Alexandru Petrescu, Behcet Saikaya, Michal Skorepa, Dave
Thaler, Joe Touch, Bernie Volz, Ryuji Wakikawa, Tony Whyman, Lloyd
Wood and James Woodyatt. Members of the IESG also provided valuable
input during their review process that greatly improved the document.
Special thanks go to Stewart Bryant, Joel Halpern and Brian Haberman
for their shepherding guidance during the publication of the AERO
first edition.
This work has further been encouraged and supported by Boeing
colleagues including Akash Agarwal, Kyle Bae, M. Wayne Benson, Dave
Bernhardt, Cam Brodie, John Bush, Balaguruna Chidambaram, Irene Chin,
Bruce Cornish, Claudiu Danilov, Sean Dickson, Don Dillenburg, Joe
Dudkowski, Wen Fang, Samad Farooqui, Anthony Gregory, Jeff Holland,
Seth Jahne, Brian Jaury, Greg Kimberly, Ed King, Madhuri Madhava
Badgandi, Laurel Matthew, Gene MacLean III, Kyle Mikos, Rob
Muszkiewicz, Sean O'Sullivan, Satish Raghavendran, Vijay Rajagopalan,
Kristina Ross, Greg Saccone, Ron Sackman, Bhargava Raman Sai Prakash,
Rod Santiago, Madhanmohan Savadamuthu, Kent Shuey, Brian Skeen, Mike
Slane, Carrie Spiker, Katie Tran, Brendan Williams, Amelia Wilson,
Julie Wulff, Yueli Yang, Eric Yeh and other members of the Boeing
mobility, networking and autonomy teams. Akash Agarwal, Kyle Bae,
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Wayne Benson, Madhuri Madhava Badgandi, Vijayasarathy Rajagopalan,
Bhargava Raman Sai Prakash, Katie Tran and Eric Yeh are especially
acknowledged for their work on the AERO implementation. Chuck
Klabunde is honored for his support and guidance, and we mourn his
untimely loss.
This work was inspired by the support and encouragement of countless
outstanding colleagues, managers and program directors over the span
of many decades. Beginning in the late 1980s,' the Digital Equipment
Corporation (DEC) Ultrix Engineering and DECnet Architects groups
identified early issues with fragmentation and bridging links with
diverse MTUs. In the early 1990s, engagements at DEC Project Sequoia
at UC Berkeley and the DEC Western Research Lab in Palo Alto included
investigations into large-scale networked filesystems, ATM vs
Internet and network security proxys. In the mid-1990s to early
2000s employment at the NASA Ames Research Center (Sterling Software)
and SRI International supported early investigations of IPv6, ONR UAV
Communications and the IETF. An employment at Nokia where important
IETF documents were published gave way to a present-day engagement
with The Boeing Company. The work matured at Boeing through major
programs including Future Combat Systems, Advanced Airplane Program,
DTN for the International Space Station, Mobility Vision Lab, CAST,
Caravan, Airplane Internet of Things, the NASA UAS/CNS program, the
FAA/ICAO ATN/IPS program and many others. An attempt to name all who
gave support and encouragement would double the current document size
and result in many unintentional omissions - but to all a humble
thanks.
Earlier works on NBMA tunneling approaches are found in
[RFC2529][RFC5214][RFC5569].
Many of the constructs presented in this second edition of AERO are
based on the author's earlier works, including:
* Intra-Site Automatic Tunnel Addressing Protocol (ISATAP) [RFC5214]
* The Subnetwork Encapsulation and Adaptation Layer (SEAL) [RFC5320]
* Virtual Enterprise Traversal (VET) [RFC5558]
* Routing and Addressing in Networks with Global Enterprise
Recursion (RANGER) [RFC5720][RFC6139]
* The Internet Routing Overlay Network (IRON) [RFC6179]
* AERO, First Edition [RFC6706]
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Note that these works cite numerous earlier efforts that are not
included here due to space limitations. The authors of those earlier
works are acknowledged for their insights.
This work is aligned with the NASA Safe Autonomous Systems Operation
(SASO) program under NASA contract number NNA16BD84C.
This work is aligned with the FAA as per the SE2025 contract number
DTFAWA-15-D-00030.
This work is aligned with the Boeing Commercial Airplanes (BCA)
Airplane Internet of Things (AIoT) and autonomy programs.
This work is aligned with the Boeing Information Technology (BIT)
MobileNet program.
This work is aligned with the Boeing/Virginia Tech National Security
Institute (VTNSI) 5G MANET research program.
Honoring life, liberty and the pursuit of happiness.
9. References
9.1. Normative References
[I-D.templin-6man-omni3]
Templin, F., "Transmission of IP Packets over Overlay
Multilink Network (OMNI) Interfaces", Work in Progress,
Internet-Draft, draft-templin-6man-omni3-73, 6 February
2026, <https://datatracker.ietf.org/doc/html/draft-
templin-6man-omni3-73>.
[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791,
DOI 10.17487/RFC0791, September 1981,
<https://www.rfc-editor.org/info/rfc791>.
[RFC0792] Postel, J., "Internet Control Message Protocol", STD 5,
RFC 792, DOI 10.17487/RFC0792, September 1981,
<https://www.rfc-editor.org/info/rfc792>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and
More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191,
November 2005, <https://www.rfc-editor.org/info/rfc4191>.
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[RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005,
<https://www.rfc-editor.org/info/rfc4193>.
[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271,
DOI 10.17487/RFC4271, January 2006,
<https://www.rfc-editor.org/info/rfc4271>.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, DOI 10.17487/RFC4291, February
2006, <https://www.rfc-editor.org/info/rfc4291>.
[RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet
Control Message Protocol (ICMPv6) for the Internet
Protocol Version 6 (IPv6) Specification", STD 89,
RFC 4443, DOI 10.17487/RFC4443, March 2006,
<https://www.rfc-editor.org/info/rfc4443>.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
DOI 10.17487/RFC4861, September 2007,
<https://www.rfc-editor.org/info/rfc4861>.
[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862,
DOI 10.17487/RFC4862, September 2007,
<https://www.rfc-editor.org/info/rfc4862>.
[RFC6437] Amante, S., Carpenter, B., Jiang, S., and J. Rajahalme,
"IPv6 Flow Label Specification", RFC 6437,
DOI 10.17487/RFC6437, November 2011,
<https://www.rfc-editor.org/info/rfc6437>.
[RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label
for Equal Cost Multipath Routing and Link Aggregation in
Tunnels", RFC 6438, DOI 10.17487/RFC6438, November 2011,
<https://www.rfc-editor.org/info/rfc6438>.
[RFC6890] Cotton, M., Vegoda, L., Bonica, R., Ed., and B. Haberman,
"Special-Purpose IP Address Registries", BCP 153,
RFC 6890, DOI 10.17487/RFC6890, April 2013,
<https://www.rfc-editor.org/info/rfc6890>.
[RFC8028] Baker, F. and B. Carpenter, "First-Hop Router Selection by
Hosts in a Multi-Prefix Network", RFC 8028,
DOI 10.17487/RFC8028, November 2016,
<https://www.rfc-editor.org/info/rfc8028>.
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[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/info/rfc8200>.
[RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A.,
Richardson, M., Jiang, S., Lemon, T., and T. Winters,
"Dynamic Host Configuration Protocol for IPv6 (DHCPv6)",
RFC 8415, DOI 10.17487/RFC8415, November 2018,
<https://www.rfc-editor.org/info/rfc8415>.
9.2. Informative References
[BGP] Huston, G., "BGP in 2015, http://potaroo.net", January
2016.
[CERF1] Cerf, V. and R. Kahn, "A Protocol for Packet Network
Intercommunication,
https://ieeexplore.ieee.org/document/1092259", May 1974.
[CERF2] Cerf, V., "The Catenet Model For Internetworking, IETF
IEN48, https://www.rfc-editor.org/ien/scanned/ien48.pdf",
July 1978.
[EUI] "IEEE Guidelines for Use of Extended Unique Identifier
(EUI), Organizationally Unique Identifier (OUI), and
Company ID, https://standards.ieee.org/wp-
content/uploads/import/documents/tutorials/eui.pdf", 3
August 2017.
[I-D.ietf-6man-rfc6724-update]
Buraglio, N., Chown, T., and J. Duncan, "Prioritizing
known-local IPv6 ULAs through address selection policy",
Work in Progress, Internet-Draft, draft-ietf-6man-rfc6724-
update-25, 11 August 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-6man-
rfc6724-update-25>.
[I-D.ietf-intarea-tunnels]
Touch, J. D. and M. Townsley, "IP Tunnels in the Internet
Architecture", Work in Progress, Internet-Draft, draft-
ietf-intarea-tunnels-15, 9 May 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-intarea-
tunnels-15>.
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[I-D.ietf-rtgwg-atn-bgp]
Templin, F., Saccone, G., Dawra, G., Lindem, A., and V.
Moreno, "A Simple BGP-based Mobile Routing System for the
Aeronautical Telecommunications Network", Work in
Progress, Internet-Draft, draft-ietf-rtgwg-atn-bgp-30, 6
February 2026, <https://datatracker.ietf.org/doc/html/
draft-ietf-rtgwg-atn-bgp-30>.
[I-D.perkins-manet-aodvv2]
Perkins, C. E., Dowdell, J., Steenbrink, L., and V.
Pritchard, "Ad Hoc On-demand Distance Vector Version 2
(AODVv2) Routing", Work in Progress, Internet-Draft,
draft-perkins-manet-aodvv2-06, 20 June 2025,
<https://datatracker.ietf.org/doc/html/draft-perkins-
manet-aodvv2-06>.
[I-D.templin-6man-mla]
Templin, F., "IPv6 Addresses for Ad Hoc Networks", Work in
Progress, Internet-Draft, draft-templin-6man-mla-30, 11
November 2025, <https://datatracker.ietf.org/doc/html/
draft-templin-6man-mla-30>.
[I-D.templin-manet-inet]
Templin, F. and D. J. Jakubisin, "MANET Internetworking:
Problem Statement and Gap Analysis", Work in Progress,
Internet-Draft, draft-templin-manet-inet-02, 12 January
2026, <https://datatracker.ietf.org/doc/html/draft-
templin-manet-inet-02>.
[KAHN] Perry, T., "The Great Interconnector, IEEE Spectrum,
https://spectrum.ieee.org/bob-kahn-2667754905", May 2024.
[POUZIN] Pouzin, L., "Interconnection of Packet Switching Networks,
http://xn--brwolff-5wa.de/public/Pouzin-1973-
Interconnection-of-Packet-Switching-Networks--INWG-Note-
42.pdf", October 1973.
[RFC1256] Deering, S., Ed., "ICMP Router Discovery Messages",
RFC 1256, DOI 10.17487/RFC1256, September 1991,
<https://www.rfc-editor.org/info/rfc1256>.
[RFC1812] Baker, F., Ed., "Requirements for IP Version 4 Routers",
RFC 1812, DOI 10.17487/RFC1812, June 1995,
<https://www.rfc-editor.org/info/rfc1812>.
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[RFC1918] Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G.
J., and E. Lear, "Address Allocation for Private
Internets", BCP 5, RFC 1918, DOI 10.17487/RFC1918,
February 1996, <https://www.rfc-editor.org/info/rfc1918>.
[RFC2236] Fenner, W., "Internet Group Management Protocol, Version
2", RFC 2236, DOI 10.17487/RFC2236, November 1997,
<https://www.rfc-editor.org/info/rfc2236>.
[RFC2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet
Networks", RFC 2464, DOI 10.17487/RFC2464, December 1998,
<https://www.rfc-editor.org/info/rfc2464>.
[RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4
Domains without Explicit Tunnels", RFC 2529,
DOI 10.17487/RFC2529, March 1999,
<https://www.rfc-editor.org/info/rfc2529>.
[RFC3056] Carpenter, B. and K. Moore, "Connection of IPv6 Domains
via IPv4 Clouds", RFC 3056, DOI 10.17487/RFC3056, February
2001, <https://www.rfc-editor.org/info/rfc3056>.
[RFC3724] Kempf, J., Ed., Austein, R., Ed., and IAB, "The Rise of
the Middle and the Future of End-to-End: Reflections on
the Evolution of the Internet Architecture", RFC 3724,
DOI 10.17487/RFC3724, March 2004,
<https://www.rfc-editor.org/info/rfc3724>.
[RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener
Discovery Version 2 (MLDv2) for IPv6", RFC 3810,
DOI 10.17487/RFC3810, June 2004,
<https://www.rfc-editor.org/info/rfc3810>.
[RFC4007] Deering, S., Haberman, B., Jinmei, T., Nordmark, E., and
B. Zill, "IPv6 Scoped Address Architecture", RFC 4007,
DOI 10.17487/RFC4007, March 2005,
<https://www.rfc-editor.org/info/rfc4007>.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, DOI 10.17487/RFC4301,
December 2005, <https://www.rfc-editor.org/info/rfc4301>.
[RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through
Network Address Translations (NATs)", RFC 4380,
DOI 10.17487/RFC4380, February 2006,
<https://www.rfc-editor.org/info/rfc4380>.
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[RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery
Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April
2006, <https://www.rfc-editor.org/info/rfc4389>.
[RFC4429] Moore, N., "Optimistic Duplicate Address Detection (DAD)
for IPv6", RFC 4429, DOI 10.17487/RFC4429, April 2006,
<https://www.rfc-editor.org/info/rfc4429>.
[RFC4511] Sermersheim, J., Ed., "Lightweight Directory Access
Protocol (LDAP): The Protocol", RFC 4511,
DOI 10.17487/RFC4511, June 2006,
<https://www.rfc-editor.org/info/rfc4511>.
[RFC4541] Christensen, M., Kimball, K., and F. Solensky,
"Considerations for Internet Group Management Protocol
(IGMP) and Multicast Listener Discovery (MLD) Snooping
Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006,
<https://www.rfc-editor.org/info/rfc4541>.
[RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick,
"Internet Group Management Protocol (IGMP) / Multicast
Listener Discovery (MLD)-Based Multicast Forwarding
("IGMP/MLD Proxying")", RFC 4605, DOI 10.17487/RFC4605,
August 2006, <https://www.rfc-editor.org/info/rfc4605>.
[RFC5015] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano,
"Bidirectional Protocol Independent Multicast (BIDIR-
PIM)", RFC 5015, DOI 10.17487/RFC5015, October 2007,
<https://www.rfc-editor.org/info/rfc5015>.
[RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site
Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214,
DOI 10.17487/RFC5214, March 2008,
<https://www.rfc-editor.org/info/rfc5214>.
[RFC5320] Templin, F., Ed., "The Subnetwork Encapsulation and
Adaptation Layer (SEAL)", RFC 5320, DOI 10.17487/RFC5320,
February 2010, <https://www.rfc-editor.org/info/rfc5320>.
[RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008,
<https://www.rfc-editor.org/info/rfc5340>.
[RFC5522] Eddy, W., Ivancic, W., and T. Davis, "Network Mobility
Route Optimization Requirements for Operational Use in
Aeronautics and Space Exploration Mobile Networks",
RFC 5522, DOI 10.17487/RFC5522, October 2009,
<https://www.rfc-editor.org/info/rfc5522>.
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[RFC5558] Templin, F., Ed., "Virtual Enterprise Traversal (VET)",
RFC 5558, DOI 10.17487/RFC5558, February 2010,
<https://www.rfc-editor.org/info/rfc5558>.
[RFC5569] Despres, R., "IPv6 Rapid Deployment on IPv4
Infrastructures (6rd)", RFC 5569, DOI 10.17487/RFC5569,
January 2010, <https://www.rfc-editor.org/info/rfc5569>.
[RFC5614] Ogier, R. and P. Spagnolo, "Mobile Ad Hoc Network (MANET)
Extension of OSPF Using Connected Dominating Set (CDS)
Flooding", RFC 5614, DOI 10.17487/RFC5614, August 2009,
<https://www.rfc-editor.org/info/rfc5614>.
[RFC5720] Templin, F., "Routing and Addressing in Networks with
Global Enterprise Recursion (RANGER)", RFC 5720,
DOI 10.17487/RFC5720, February 2010,
<https://www.rfc-editor.org/info/rfc5720>.
[RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,
<https://www.rfc-editor.org/info/rfc5880>.
[RFC6081] Thaler, D., "Teredo Extensions", RFC 6081,
DOI 10.17487/RFC6081, January 2011,
<https://www.rfc-editor.org/info/rfc6081>.
[RFC6106] Jeong, J., Park, S., Beloeil, L., and S. Madanapalli,
"IPv6 Router Advertisement Options for DNS Configuration",
RFC 6106, DOI 10.17487/RFC6106, November 2010,
<https://www.rfc-editor.org/info/rfc6106>.
[RFC6139] Russert, S., Ed., Fleischman, E., Ed., and F. Templin,
Ed., "Routing and Addressing in Networks with Global
Enterprise Recursion (RANGER) Scenarios", RFC 6139,
DOI 10.17487/RFC6139, February 2011,
<https://www.rfc-editor.org/info/rfc6139>.
[RFC6145] Li, X., Bao, C., and F. Baker, "IP/ICMP Translation
Algorithm", RFC 6145, DOI 10.17487/RFC6145, April 2011,
<https://www.rfc-editor.org/info/rfc6145>.
[RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
NAT64: Network Address and Protocol Translation from IPv6
Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146,
April 2011, <https://www.rfc-editor.org/info/rfc6146>.
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[RFC6147] Bagnulo, M., Sullivan, A., Matthews, P., and I. van
Beijnum, "DNS64: DNS Extensions for Network Address
Translation from IPv6 Clients to IPv4 Servers", RFC 6147,
DOI 10.17487/RFC6147, April 2011,
<https://www.rfc-editor.org/info/rfc6147>.
[RFC6179] Templin, F., Ed., "The Internet Routing Overlay Network
(IRON)", RFC 6179, DOI 10.17487/RFC6179, March 2011,
<https://www.rfc-editor.org/info/rfc6179>.
[RFC6296] Wasserman, M. and F. Baker, "IPv6-to-IPv6 Network Prefix
Translation", RFC 6296, DOI 10.17487/RFC6296, June 2011,
<https://www.rfc-editor.org/info/rfc6296>.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
January 2012, <https://www.rfc-editor.org/info/rfc6347>.
[RFC6621] Macker, J., Ed., "Simplified Multicast Forwarding",
RFC 6621, DOI 10.17487/RFC6621, May 2012,
<https://www.rfc-editor.org/info/rfc6621>.
[RFC6706] Templin, F., Ed., "Asymmetric Extended Route Optimization
(AERO)", RFC 6706, DOI 10.17487/RFC6706, August 2012,
<https://www.rfc-editor.org/info/rfc6706>.
[RFC6724] Thaler, D., Ed., Draves, R., Matsumoto, A., and T. Chown,
"Default Address Selection for Internet Protocol Version 6
(IPv6)", RFC 6724, DOI 10.17487/RFC6724, September 2012,
<https://www.rfc-editor.org/info/rfc6724>.
[RFC7181] Clausen, T., Dearlove, C., Jacquet, P., and U. Herberg,
"The Optimized Link State Routing Protocol Version 2",
RFC 7181, DOI 10.17487/RFC7181, April 2014,
<https://www.rfc-editor.org/info/rfc7181>.
[RFC7296] Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T.
Kivinen, "Internet Key Exchange Protocol Version 2
(IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October
2014, <https://www.rfc-editor.org/info/rfc7296>.
[RFC7333] Chan, H., Ed., Liu, D., Seite, P., Yokota, H., and J.
Korhonen, "Requirements for Distributed Mobility
Management", RFC 7333, DOI 10.17487/RFC7333, August 2014,
<https://www.rfc-editor.org/info/rfc7333>.
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[RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I.,
Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent
Multicast - Sparse Mode (PIM-SM): Protocol Specification
(Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March
2016, <https://www.rfc-editor.org/info/rfc7761>.
[RFC8175] Ratliff, S., Jury, S., Satterwhite, D., Taylor, R., and B.
Berry, "Dynamic Link Exchange Protocol (DLEP)", RFC 8175,
DOI 10.17487/RFC8175, June 2017,
<https://www.rfc-editor.org/info/rfc8175>.
[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/info/rfc8402>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>.
[RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
(SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,
<https://www.rfc-editor.org/info/rfc8754>.
[RFC8966] Chroboczek, J. and D. Schinazi, "The Babel Routing
Protocol", RFC 8966, DOI 10.17487/RFC8966, January 2021,
<https://www.rfc-editor.org/info/rfc8966>.
[RFC9000] Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
Multiplexed and Secure Transport", RFC 9000,
DOI 10.17487/RFC9000, May 2021,
<https://www.rfc-editor.org/info/rfc9000>.
[RFC9365] Jeong, J., Ed., "IPv6 Wireless Access in Vehicular
Environments (IPWAVE): Problem Statement and Use Cases",
RFC 9365, DOI 10.17487/RFC9365, March 2023,
<https://www.rfc-editor.org/info/rfc9365>.
[RFC9762] Colitti, L., Linkova, J., Ma, X., Ed., and D. Lamparter,
"Using Router Advertisements to Signal the Availability of
DHCPv6 Prefix Delegation to Clients", RFC 9762,
DOI 10.17487/RFC9762, June 2025,
<https://www.rfc-editor.org/info/rfc9762>.
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Appendix A. Non-Normative Considerations
AERO can be applied to a multitude of Internetworking scenarios, with
each having its own adaptations. The following considerations are
provided as non-normative guidance:
A.1. Implementation Strategies for Route Optimization
Address resolution and route optimization as discussed in
Section 4.13 results in the creation of NCEs. The NCE state is set
to REACHABLE for at most ReachableTime seconds. In order to refresh
the NCE lifetime before the ReachableTime timer expires, the
specification requires implementations to issue a new NS/NA(AR)
exchange to reset ReachableTime while data messages are still
flowing. However, the decision of when to initiate a new NS/NA(AR)
exchange and to perpetuate the process is left as an implementation
detail.
One possible strategy may be to monitor the NCE watching for data
messages for (ReachableTime - 5) seconds. If any data messages have
been sent to the neighbor within this timeframe, then send an NS(AR)
to receive a new NA(AR). If no data messages have been sent, wait
for 5 additional seconds and send an immediate NS(AR) if any data
packets are sent within this "expiration pending" 5 second window.
If no additional data messages are sent within the 5 second window,
reset the NCE state to STALE.
The monitoring of the neighbor data traffic therefore becomes an
ongoing process during the NCE lifetime. If the NCE expires, future
data messages will trigger a new NS/NA(AR) exchange while the
messages themselves may be delivered over longer paths until route
optimization state is re-established.
A.2. Implicit Mobility Management
OMNI interface neighbors MAY provide a configuration option that
allows them to perform implicit mobility management in which no IPv6
ND messaging is used. In that case, the Client only transmits
carrier packets over a single interface at a time, and the neighbor
always observes carrier packets arriving from the Client from the
same underlay Source Address.
If the Client's underlay interface address changes (either due to a
readdressing of the original interface or switching to a new
interface) the neighbor immediately updates the NCE for the Client
and begins accepting and sending carrier packets according to the
Client's new address. This implicit mobility method applies to use
cases such as cellphones with both WiFi and Cellular interfaces where
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only one of the interfaces is active at a given time, and the Client
automatically switches over to the backup interface if the primary
interface fails.
A.3. Direct Underlying Interfaces
When a Client's OMNI interface is configured over a Direct interface,
the neighbor at the other end of the Direct link can receive original
IP packets without any encapsulation. In that case, the Client sends
packets over the Direct link according to traffic selectors. If the
Direct interface is selected, then the Client's packets are
transmitted directly to the peer without traversing an ANET/INET. If
other interfaces are selected, then the Client's packets are
transmitted via a different interface, which may result in the
inclusion of Proxy/Servers and Gateways in the communications path.
Direct interfaces must be tested periodically for reachability, e.g.,
via NUD.
A.4. AERO Critical Infrastructure Considerations
AERO Gateways can be either Commercial off-the Shelf (COTS) standard
IP routers or virtual machines in the cloud. Gateways must be
provisioned, supported and managed by the INET administrative
authority, and connected to the Gateways of other INETs via inter-
domain peerings. Cost for purchasing, configuring and managing
Gateways is nominal even for very large OMNI links.
AERO INET Proxy/Servers can be standard dedicated server platforms,
but most often will be deployed as virtual machines in the cloud.
The only requirements for INET Proxy/Servers are that they can run
the AERO/OMNI code and have at least one network interface connection
to the INET. INET Proxy/Servers must be provisioned, supported and
managed by the INET administrative authority. Cost for purchasing,
configuring and managing cloud Proxy/Servers is nominal especially
for virtual machines.
AERO ANET Proxy/Servers are most often standard dedicated server
platforms with one underlay interface connected to the ANET and a
second interface connected to an INET. As with INET Proxy/Servers,
the only requirements are that they can run the AERO/OMNI code and
have at least one interface connection to the INET. ANET Proxy/
Servers must be provisioned, supported and managed by the ANET
administrative authority. Cost for purchasing, configuring and
managing Proxys is nominal, and borne by the ANET administrative
authority.
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AERO Relays are simply Proxy/Servers connected to INETs and/or EUNs
that provide forwarding services for non-MNP destinations. The Relay
connects to the OMNI link and engages in eBGP peering with one or
more Gateways as a stub AS. The Relay then injects its MNPs and/or
non-MNP prefixes into the BGP routing system, and provisions the
prefixes to its downstream-attached networks. The Relay can perform
ARS/ARR services the same as for any Proxy/Server, and can route
between the MNP and non-MNP address spaces.
A.5. AERO Server Failure Implications
AERO Proxy/Servers do not present a single point of failure in the
architecture since all Proxy/Servers on the link provide identical
services and loss of a Proxy/Server does not imply immediate and/or
comprehensive communication failures. Proxy/Server failure can be
quickly detected and conveyed by Bidirectional Forward Detection
(BFD) and/or proactive NUD allowing Clients to migrate to new Proxy/
Servers.
If a Proxy/Server fails, peer carrier packet forwarding to Clients
will continue by virtue of the NCEs that have already been
established through address resolution and route optimization. If a
Client also experiences mobility events at roughly the same time the
Proxy/Server fails, uNA messages may be lost but NCEs in the DEPARTED
state will ensure that carrier packet forwarding to the Client's new
locations will continue for up to DepartTime seconds.
If a Client is left without a Proxy/Server for a considerable length
of time (e.g., greater than ReachableTime seconds) then existing NCEs
will eventually expire and both ongoing and new communications will
fail. The original source will continue to retransmit until the
Client has established a new Proxy/Server relationship, after which
time communications can continue .
Therefore, links that provide many Proxy/Servers with high
availability profiles are responsive to loss of individual
infrastructure elements, since Clients can quickly establish new
Proxy/Server relationships in event of failures.
A.6. AERO Client / Server Architecture
The AERO architectural model is client / server in the control plane,
with route optimization in the data plane. The same as for common
Internet services, the AERO Client discovers the addresses of AERO
Proxy/Servers and connects to one or more of them. The AERO service
is analogous to common Internet services such as google.com,
yahoo.com, cnn.com, etc. However, there is only one AERO service for
the link and all Proxy/Servers provide identical services.
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Common Internet services provide differing strategies for advertising
server addresses to clients. The strategy is conveyed through the
DNS resource records returned in response to name resolution queries.
As of January 2020 Internet-based 'nslookup' services were used to
determine the following:
* When a client resolves the domainname "google.com", the DNS always
returns one A record (i.e., an IPv4 address) and one AAAA record
(i.e., an IPv6 address). The client receives the same addresses
each time it resolves the domainname via the same DNS resolver,
but may receive different addresses when it resolves the
domainname via different DNS resolvers. But, in each case,
exactly one A and one AAAA record are returned.
* When a client resolves the domainname "ietf.org", the DNS always
returns one A record and one AAAA record with the same addresses
regardless of which DNS resolver is used.
* When a client resolves the domainname "yahoo.com", the DNS always
returns a list of 4 A records and 4 AAAA records. Each time the
client resolves the domainname via the same DNS resolver, the same
list of addresses are returned but in randomized order (i.e.,
consistent with a DNS round-robin strategy). But, interestingly,
the same addresses are returned (albeit in randomized order) when
the domainname is resolved via different DNS resolvers.
* When a client resolves the domainname "amazon.com", the DNS always
returns a list of 3 A records and no AAAA records. As with
"yahoo.com", the same three A records are returned from any
worldwide Internet connection point in randomized order.
The above example strategies show differing approaches to Internet
resilience and service distribution offered by major Internet
services. The Google approach exposes only a single IPv4 and a
single IPv6 address to clients. Clients can then select whichever IP
protocol version offers the best response, but will always use the
same IP address according to the current Internet connection point.
This means that the IP address offered by the network must lead to a
highly-available server and/or service distribution point. In other
words, resilience is predicated on high availability within the
network and with no client-initiated failovers expected (i.e., it is
all-or-nothing from the client's perspective). However, Google does
provide for worldwide distributed service distribution by virtue of
the fact that each Internet connection point responds with a
different IPv6 and IPv4 address. The IETF approach is like google
(all-or-nothing from the client's perspective), but provides only a
single IPv4 or IPv6 address on a worldwide basis. This means that
the addresses must be made highly-available at the network level with
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no client failover possibility, and if there is any worldwide service
distribution it would need to be conducted by a network element that
is reached via the IP address acting as a service distribution point.
In contrast to the Google and IETF philosophies, Yahoo and Amazon
both provide clients with a (short) list of IP addresses with Yahoo
providing both IP protocol versions and Amazon as IPv4-only. The
order of the list is randomized with each name service query
response, with the effect of round-robin load balancing for service
distribution. With a short list of addresses, there is still
expectation that the network will implement high availability for
each address but in case any single address fails the client can
switch over to using a different address. The balance then becomes
one of function in the network vs function in the end system.
The same implications observed for common highly-available services
in the Internet apply also to the AERO client/server architecture.
When an AERO Client connects to one or more ANETs, it discovers one
or more AERO Proxy/Server addresses through the mechanisms discussed
in earlier sections. Each Proxy/Server address presumably leads to a
fault-tolerant clustering arrangement such as supported by Linux-HA,
Extended Virtual Synchrony or Paxos. Such an arrangement has
precedence in common Internet service deployments in lightweight
virtual machines without requiring expensive hardware deployment.
Similarly, common Internet service deployments set service IP
addresses on service distribution points that may relay requests to
many different servers.
For AERO, the expectation is that a combination of the Google/IETF
and Yahoo/Amazon philosophies would be employed. The AERO Client
connects to different ANET access points and can receive 1-2 Proxy/
Server ULAs at each point. It then selects one AERO Proxy/Server
address, and engages in RS/RA exchanges with the same Proxy/Server
from all ANET connections. The Client remains with this Proxy/Server
unless or until the Proxy/Server fails, in which case it can switch
over to an alternate Proxy/Server. The Client can likewise switch
over to a different Proxy/Server at any time if there is some reason
for it to do so. So, the AERO expectation is for a balance of
function in the network and end system, with fault tolerance and
resilience at both levels.
Appendix B. Change Log
<< RFC Editor - remove prior to publication >>
Differences from earlier versions:
Draft -55 to -57
Templin Expires 29 August 2026 [Page 97]
Internet-Draft AERO February 2026
* Final version; future updates to appear in amendments draft.
* Clarification on SRH addressing; ICMPv6 message code
description change.
Draft -54 to -55
* Simplified Multilink Forwarding messages now based only on MP
control messages which are ordinary IP packets with OMNI option
trailers.
Draft -53 to -54
* Removed defunct specification on Segment Routing.
Draft -52 to -53
* Support marking non IPv6 ND messages as control.
* OMNI interface LLA clarifications.
Draft -50 to -52
* Fully embraced segment routing and Segment Routing Topology.
* Fully embraced MLA addressing and removed PNP addressing.
* Updated historical background.
* Clarified IPv6 ND message Source, Destination and Target
addressing.
* Clarified that AFVI is now an SRH TLV option.
Author's Address
Fred L. Templin (editor)
Boeing Technology Innovation
P.O. Box 3707
Seattle, WA 98124
United States of America
Email: [email protected]
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