Automatic Extended Route Optimization (AERO)
draft-templin-intarea-aero-29
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft whose latest revision state is "Replaced".
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|---|---|---|---|
| Author | Fred Templin | ||
| Last updated | 2023-05-04 (Latest revision 2023-04-03) | ||
| Replaces | draft-templin-6man-aero | ||
| Replaced by | draft-templin-intarea-aero2 | ||
| RFC stream | (None) | ||
| Formats | |||
| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
| RFC Editor Note | (None) | ||
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draft-templin-intarea-aero-29
Network Working Group F. L. Templin, Ed.
Internet-Draft Boeing Research & Technology
Intended status: Standards Track 4 May 2023
Expires: 5 November 2023
Automatic Extended Route Optimization (AERO)
draft-templin-intarea-aero-29
Abstract
This document specifies an Automatic Extended Route Optimization
(AERO) service for IP internetworking over Overlay Multilink Network
(OMNI) interfaces. AERO/OMNI use an IPv6 unique-local address format
for IPv6 Neighbor Discovery (IPv6 ND) messaging over the OMNI virtual
link. Router discovery and neighbor coordination are employed for
network admission and to manage the OMNI link forwarding and routing
systems. 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 mobile internetworking
service especially well-suited to aviation, intelligent
transportation systems, mobile end user devices and many other
applications.
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
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
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 5 November 2023.
Copyright Notice
Copyright (c) 2023 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
and restrictions with respect to this document. Code Components
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 17
4. Automatic Extended Route Optimization (AERO) . . . . . . . . 17
4.1. AERO Node Types . . . . . . . . . . . . . . . . . . . . . 17
4.2. The AERO Service over OMNI Links . . . . . . . . . . . . 19
4.2.1. AERO/OMNI Reference Model . . . . . . . . . . . . . . 19
4.2.2. Addressing and Node Identification . . . . . . . . . 23
4.2.3. AERO Routing System . . . . . . . . . . . . . . . . . 24
4.2.4. Segment Routing Topologies (SRTs) . . . . . . . . . . 26
4.2.5. Segment Routing For OMNI Link Selection . . . . . . . 27
4.3. OMNI Interface Characteristics . . . . . . . . . . . . . 27
4.4. OMNI Interface Initialization . . . . . . . . . . . . . . 29
4.4.1. AERO Proxy/Server and Relay Behavior . . . . . . . . 30
4.4.2. AERO Client Behavior . . . . . . . . . . . . . . . . 30
4.4.3. AERO Host Behavior . . . . . . . . . . . . . . . . . 31
4.4.4. AERO Gateway Behavior . . . . . . . . . . . . . . . . 31
4.5. OMNI Interface Neighbor Cache Maintenance . . . . . . . . 31
4.5.1. OMNI ND Messages . . . . . . . . . . . . . . . . . . 34
4.5.2. OMNI Neighbor Advertisement Message Flags . . . . . . 37
4.5.3. OMNI Neighbor Window Synchronization . . . . . . . . 37
4.6. OMNI Interface Encapsulation and Fragmentation . . . . . 38
4.7. OMNI Interface Decapsulation . . . . . . . . . . . . . . 40
4.8. OMNI Interface Data Origin Authentication . . . . . . . . 41
4.9. OMNI Interface MTU . . . . . . . . . . . . . . . . . . . 42
4.10. OMNI Interface Forwarding Algorithm . . . . . . . . . . . 42
4.10.1. Host Forwarding Algorithm . . . . . . . . . . . . . 44
4.10.2. Client Forwarding Algorithm . . . . . . . . . . . . 45
4.10.3. Proxy/Server and Relay Forwarding Algorithm . . . . 46
4.10.4. Gateway Forwarding Algorithm . . . . . . . . . . . . 48
4.11. OMNI Interface Error Handling . . . . . . . . . . . . . . 50
4.12. AERO Mobility Service Coordination . . . . . . . . . . . 53
4.12.1. AERO Service Model . . . . . . . . . . . . . . . . . 53
4.12.2. AERO Host and Client Behavior . . . . . . . . . . . 54
4.12.3. AERO Proxy/Server Behavior . . . . . . . . . . . . . 55
4.13. AERO Address Resolution, Multilink Forwarding and Route
Optimization . . . . . . . . . . . . . . . . . . . . . . 62
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4.13.1. Multilink Address Resolution . . . . . . . . . . . . 63
4.13.2. Multilink Forwarding . . . . . . . . . . . . . . . . 68
4.13.3. Mobile Ad-hoc Network (MANET) Forwarding . . . . . . 82
4.13.4. Client/Gateway Route Optimization . . . . . . . . . 85
4.13.5. Client/Client Route Optimization . . . . . . . . . . 87
4.13.6. Intra-ANET/ENET Route Optimization for AERO Peers . 89
4.14. Neighbor Unreachability Detection (NUD) . . . . . . . . . 89
4.15. Mobility Management and Quality of Service (QoS) . . . . 91
4.15.1. Mobility Update Messaging . . . . . . . . . . . . . 91
4.15.2. Announcing Link-Layer Information Changes . . . . . 92
4.15.3. Bringing New Links Into Service . . . . . . . . . . 93
4.15.4. Deactivating Existing Links . . . . . . . . . . . . 93
4.15.5. Moving Between Proxy/Servers . . . . . . . . . . . . 93
4.16. Multicast . . . . . . . . . . . . . . . . . . . . . . . . 95
4.16.1. Source-Specific Multicast (SSM) . . . . . . . . . . 95
4.16.2. Any-Source Multicast (ASM) . . . . . . . . . . . . . 96
4.16.3. Bi-Directional PIM (BIDIR-PIM) . . . . . . . . . . . 97
4.17. Operation over Multiple OMNI Links . . . . . . . . . . . 97
4.18. DNS Considerations . . . . . . . . . . . . . . . . . . . 98
4.19. Transition/Coexistence Considerations . . . . . . . . . . 98
4.20. Proxy/Server-Gateway Bidirectional Forwarding
Detection . . . . . . . . . . . . . . . . . . . . . . . 99
4.21. Time-Varying MNPs . . . . . . . . . . . . . . . . . . . . 99
5. Implementation Status . . . . . . . . . . . . . . . . . . . . 100
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 100
7. Security Considerations . . . . . . . . . . . . . . . . . . . 100
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 103
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 105
9.1. Normative References . . . . . . . . . . . . . . . . . . 105
9.2. Informative References . . . . . . . . . . . . . . . . . 106
Appendix A. Non-Normative Considerations . . . . . . . . . . . . 112
A.1. Implementation Strategies for Route Optimization . . . . 112
A.2. Implicit Mobility Management . . . . . . . . . . . . . . 113
A.3. Direct Underlying Interfaces . . . . . . . . . . . . . . 113
A.4. AERO Critical Infrastructure Considerations . . . . . . . 114
A.5. AERO Server Failure Implications . . . . . . . . . . . . 115
A.6. AERO Client / Server Architecture . . . . . . . . . . . . 115
Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 117
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 117
1. Introduction
Automatic Extended Route Optimization (AERO) fulfills the
requirements of Distributed Mobility Management (DMM) [RFC7333] and
route optimization [RFC5522] for aeronautical networking and other
network mobility use cases including intelligent transportation
systems and enterprise mobile device users. AERO is a secure
internetworking and mobility management service that employs the
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Overlay Multilink Network Interface (OMNI) [I-D.templin-intarea-omni]
Non-Broadcast, Multiple Access (NBMA) virtual link model. The OMNI
link is a virtual overlay manifested by IPv6 encapsulation and
configured over a network-of-networks concatenation of underlay
Internetworks. Nodes on the link can exchange original IP packets or
parcels [I-D.templin-intarea-parcels] as single-hop neighbors - both
IP protocol versions (IPv4 and IPv6) are supported. The OMNI
Adaptation Layer (OAL) supports multilink operation for increased
reliability and path optimization while providing fragmentation and
reassembly services to support improved performance and Maximum
Transmission Unit (MTU) diversity. This specification provides a
mobility service architecture companion to the OMNI specification.
The AERO service connects Hosts and Clients as OMNI link neighbors
via Proxy/Servers and Relays as intermediate nodes as necessary; 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 uses an IPv6 unique-local address format that
supports operation of the IPv6 Neighbor Discovery (IPv6 ND) protocol
[RFC4861]. A Client's OMNI interface can be configured over multiple
underlay interfaces, and therefore appears as a single interface with
multiple link layer addresses. Each link layer address is subject to
change due to mobility and/or multilink fluctuations, and link layer
address changes are signaled by ND messaging the same as for any IPv6
link.
AERO provides a secure cloud-based service where mobile node Clients
use Proxy/Servers acting as proxys and/or designated routers while
fixed nodes may use any Relay on the link for efficient
communications. Fixed nodes forward original IP packets/parcels
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, and Clients may
efficiently move between locations while maintaining continuous
communications with correspondents using stable IP Addresses not
subject to dynamic fluctuations.
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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
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. Relays
provide an optimal route from (fixed) correspondent nodes on underlay
Internetworks to (mobile or fixed) nodes on the OMNI link. From the
perspective of underlay Internetworks, each Relay appears as the
source of a route to the MSP; hence uplink traffic to mobile nodes is
naturally routed to the nearest Relay.
AERO can be used with OMNI links that span private-use Internetworks
and/or public Internetworks such as the global 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 robust traversal of NATs while
avoiding "triangle routing" and critical infrastructure traffic
concentration through a service known as "route optimization" is
therefore provided.
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 VPN or non-VPN services enabled according to the appropriate
security model. AERO also supports terrestrial vehicular, urban air
mobility and mobile pedestrian communication services for future
intelligent transportation systems
[I-D.ietf-ipwave-vehicular-networking]. Other applicable use cases
are also in scope.
Along with OMNI, AERO provides secured optimal routing support for
the "6 M's of Modern Internetworking", including:
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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.
2. Multinet - the ability to span the OMNI link over a segment
routing topology with multiple diverse administrative domain
network segments while maintaining seamless end-to-end
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 node vehicle-to-vehicle relaying capability
useful when multiple forwarding hops between vehicles may be
necessary to "reach back" to an infrastructure access point
connection to the OMNI link.
6. Maximization - the ability to exchange large packets/parcels
between peers without loss due to a link size restriction, and to
dynamically adjust packet/parcel 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-intarea-omni] and the
IPv6 Neighbor Discovery [RFC4861] node variables, protocol constants
and messages (including Router Solicitation (RS), Router
Advertisement (RS), Neighbor Solicitation (NS), Neighbor
Advertisement (NA), unsolicited NA (uNA) and Redirect) are cited
extensively throughout.
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Throughout the document, the simple terms "Host", "Client", "Proxy/
Server", "Gateway" and "Relay" refer to "AERO/OMNI Host", "AERO/OMNI
Client", "AERO/OMNI Proxy/Server", "AERO/OMNI Gateway" and "AERO/OMNI
Relay", respectively. Capitalization is used to distinguish these
terms from other common Internetworking uses in which they appear
without capitalization, and implies that the node in question both
configures an OMNI interface and engages the OMNI Adaptation Layer.
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 defines 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 terms "IP jumbogram", "advanced jumbo" and "IP parcel" refer to
special large packet formats discussed in detail in
[I-D.templin-intarea-parcels].
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-intarea-omni].
IPv6 Prefix Delegation
a networking service for delegating IPv6 prefixes to nodes on the
link. The nominal service is DHCPv6 [RFC8415], however alternate
services (e.g., based on IPv6 ND messaging) are also in scope. A
minimal form of prefix delegation known as "prefix registration"
can be used if the Client knows its prefix in advance and can
represent it in the source address of an IPv6 ND message.
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L3
The Network layer in the OSI network model. Also known as "layer
3", "IP layer", etc.
L2
The Data Link layer in the OSI network model. Also known as
"layer 2", "link layer", "sub-IP layer", etc.
Adaptation layer
An encapsulation mid-layer that adapts L3 to a diverse collection
of L2 underlay interfaces and their encapsulations. (No layer
number is assigned, since numbering was an artifact of the legacy
reference model that need not carry forward in the modern
architecture.) The adaptation layer sees the network layer as
"L3" and sees all link layer encapsulations as "L2
encapsulations", which may include UDP, IP and true link layer
(e.g., Ethernet, etc.) headers.
Access Network (ANET)
a connected network region (e.g., an aviation radio access
network, satellite service provider network, cellular operator
network, WiFi network, etc.) that joins Clients to the Mobility
Service. Physical and/or data link level security is assumed, and
sometimes referred to as "protected spectrum". 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.
Internetwork (INET)
a connected network region with a coherent IP addressing plan that
provides transit forwarding services between 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 (ENET)
a simple or complex "downstream" network tethered to a Client as a
single logical unit that travels together. The ENET could be as
simple as a single link connecting a single Host, or as complex as
a large network with many links, routers, bridges and end user
devices. The ENET 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. The ENET can also support a recursively-descending
chain of additional Clients such that the ENET of an upstream
Client is seen as the ANET of a downstream Client.
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{A,I,E}NET interface
a node's attachment to a link in an {A,I,E}NET.
underlay network/interface
an ANET/INET/ENET network/interface over which an OMNI interface
is configured. The OMNI interface is seen as a network layer (L3)
interface by the IP layer, and the OMNI adaptation layer sees the
underlay interface as a data link layer (L2) interface. The
underlay interface either connects directly to the physical
communications media or coordinates with another node where the
physical media is hosted.
Mobile Ad-hoc NETwork (MANET)
a connected network region that shares the same properties as an
ANET except that physical and/or data link layer security cannot
always be assumed and multihop forwarding between Clients acting
as MANET routers may be necessary. Proxy/Servers that connect the
MANET to outside networks act as Clients on their MANET interfaces
and act as ordinary Proxy/Servers on their ANET/INET interfaces,
while Clients configure MANET interfaces and provide a multihop
forwarding service for other Clients.
MANET Interface
a node's underlay interface connection to a local network with
indeterminant neighborhood properties over which multihop relaying
may be necessary.
OMNI link
the same as defined in [I-D.templin-intarea-omni]. The OMNI link
employs IPv6 encapsulation [RFC2473] to traverse intermediate
nodes 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] to navigate between different OMNI
links, and/or to cause packets/parcels to visit selected waypoints
within the same OMNI link.
OMNI Adaptation Layer (OAL)
an OMNI interface sublayer service that encapsulates original IP
packets/parcels 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.
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OMNI Interface
a node's attachment to an OMNI link. Since OMNI interface
addresses are managed for uniqueness, OMNI interfaces do not
require Duplicate Address Detection (DAD) and therefore set the
administrative variable 'DupAddrDetectTransmits' to zero
[RFC4862].
(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 is seen as a separate OMNI link segment as
discussed throughout this document.)
(OMNI) L2 encapsulation
the 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 {A,I,E}NET underlay network
partition. Common L2 encapsulation combinations include UDP/IP/
Ethernet, etc. using a port/protocol/type number for OMNI.
L2 address (L2ADDR)
an address that appears in the L2 encapsulation for an underlay
interface and also in IPv6 ND message OMNI options. L2ADDR 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 considered an
ancillary extension of the IP L2ADDR.)
original IP packet/parcel
a whole IP packet/parcel or fragment admitted into the OMNI
interface by the network layer prior to OAL encapsulation and
fragmentation, or an IP packet delivered to the network layer by
the OMNI interface following OAL decapsulation and reassembly.
OAL packet
an original IP packet/parcel encapsulated in an OAL IPv6 header
before OAL fragmentation, or following OAL reassembly.
OAL fragment
a portion of an OAL packet following fragmentation but prior to L2
encapsulation, or following L2 decapsulation but prior to OAL
reassembly.
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(OAL) atomic fragment
an OAL packet that can be forwarded without fragmentation, but
still includes a Fragment Header with a valid Identification value
and with Fragment Offset and More Fragments both set to 0.
(OAL) carrier packet
an encapsulated OAL packet/fragment following L2 encapsulation or
prior to L2 decapsulation. OAL sources and destinations exchange
carrier packets over underlay interfaces, and may be separated by
one or more OAL intermediate nodes. OAL intermediate nodes re-
encapsulate OAL packets/fragments during forwarding by removing
the L2 headers of the previous hop underlay network and replacing
them with new L2 headers for the next hop underlay network.
OAL source
an OMNI interface acts as an OAL source when it encapsulates
original IP packets/parcels to form OAL packets, then performs OAL
fragmentation and L2 encapsulation to create carrier packets.
OAL destination
an OMNI interface acts as an OAL destination when it decapsulates
carrier packets, then performs OAL reassembly and decapsulation to
derive the original IP packet/parcel.
OAL intermediate node
an OMNI interface acts as an OAL intermediate node when it removes
the L2 headers of carrier packets received from a previous hop,
then re-encapsulates the enclosed OAL packets/fragments in new L2
headers and sends these new carrier packets to the next hop. OAL
intermediate nodes decrement the OAL Hop Limit during forwarding,
and discard the OAL packet/fragment if the Hop Limit reaches 0.
OAL intermediate nodes do not decrement the TTL/Hop Limit of the
original IP packet/parcel.
Mobility Service Prefix (MSP)
an aggregated IP Global Unicast Address (GUA) prefix (e.g.,
2001:db8::/32, 192.0.2.0/24, etc.) assigned to the OMNI link and
from which more-specific Mobile Network Prefixes (MNPs) are
delegated. 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-intarea-omni]). OMNI links that connect to the
global Internet advertise their MSPs to their interdomain routing
peers.
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Mobile Network Prefix (MNP)
a longer IP prefix delegated from an MSP (e.g.,
2001:db8:1000:2000::/56, 192.0.2.8/30, etc.) and delegated to an
AERO Client or Relay.
Interface Identifier (IID)
the least significant 64 bits of an IPv6 address, as specified in
the IPv6 addressing architecture [RFC4291].
Link Local Address (LLA)
an IPv6 address beginning with fe80::/64 per the IPv6 addressing
architecture [RFC4291] and with either a 64-bit MNP (LLA-MNP) or a
56-bit random value (LLA-RND) encoded in the IID as specified in
[I-D.templin-intarea-omni].
Unique Local Address (ULA)
an IPv6 address beginning with fd00::/8 followed by a 40-bit
Global ID followed by a 16-bit Subnet ID per [RFC4193] and with
either a 64-bit MNP (ULA-MNP) or a 56-bit random value (ULA-RND)
encoded in the IID as specified in [I-D.templin-intarea-omni].
(Note that [RFC4193] specifies a second form of ULAs based on the
prefix fc00::/8, which are referred to as "ULA-C" throughout this
document to distinguish them from the ULAs defined here.)
Temporary Local Address (TLA)
a ULA beginning with fd00::/16 followed by a 48-bit randomly-
initialized value followed by an MNP-based (TLA-MNP) or random
(TLA-RND) IID as specified in [I-D.templin-intarea-omni]. Clients
use TLAs to bootstrap autoconfiguration in the presence of OMNI
link infrastructure or for sustained communications in the absence
of infrastructure. (Note that in some environments Clients can
instead use a (Hierarchical) Host Identity Tag ((H)HIT) instead of
a TLA - see: [I-D.templin-intarea-omni].)
eXtended Local Address (XLA)
a ULA beginning with fd00::/64 followed by an MNP-based (XLA-MNP)
or random (XLA-RND) IID as specified in
[I-D.templin-intarea-omni]. An XLA can be used to supply a stable
address for IPv6 ND messaging, a routing table entry for the OMNI
link routing system, etc. (Note that XLAs can also be statelessly
formed from LLAs (and vice-versa) simply by inverting prefix bits
7 and 8.)
AERO node
a node that is connected to an OMNI link and participates in the
AERO internetworking and mobility service.
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AERO Host ("Host")
an AERO node that configures an OMNI interface over an ENET
underlying interface serviced by an upstream Client. The Host
does not assign an LLA or ULA to the OMNI interface, but instead
assigns the address taken from the ENET underlying interface.
When an AERO host forwards an original IP packet/parcel to another
AERO node on the same ENET, it uses simple IP-in-L2 OMNI
encapsulation without including an OAL encapsulation header. The
Host is therefore an OMNI link termination endpoint. (Note: as an
implementation matter, the Host may instead configure the "OMNI
interface" as a virtual sublayer of the underlay interface
itself.)
AERO Client ("Client")
an AERO node that configures an OMNI interface over one or more
underlay interfaces and requests MNP delegation/registration
service from AERO Proxy/Servers. The Client assigns an XLA-MNP
(as well as Proxy/Server-specific ULA-MNPs) to the OMNI interface
for use in IPv6 ND exchanges with other AERO nodes and forwards
original IP packets/parcels to correspondents according to OMNI
interface neighbor cache state. The Client coordinates with
Proxy/Servers and/or other Clients over upstream ANET/INET
interfaces and may also provide Proxy/Server services for Hosts
and/or other Clients over downstream ENET interfaces.
AERO Proxy/Server ("Proxy/Server")
a node that provides a proxying service between AERO Clients and
external peers on its Client-facing 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 ANET
interfaces.) The Proxy/Server configures an OMNI interface and
assigns a ULA-RND to support the operation of IPv6 ND services,
while advertising any associated MNPs for which it is acting as a
hub via BGP peerings with AERO Gateways.
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AERO Relay ("Relay")
a Proxy/Server that provides forwarding services between nodes
reached via the OMNI link and correspondents on other links/
networks. AERO Relays assign a ULA-RND to an OMNI interface and
maintain BGP peerings with Gateways the same as Proxy/Servers.
Relays also run a dynamic routing protocol to discover any non-MNP
IP GUA routes in service on other links/networks, advertise OMNI
link MSP(s) to other links/networks, and redistribute routes
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 Internet can also be configured to advertise
"default" routes into the OMNI link BGP routing system.)
AERO Gateway ("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 nodes
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 MNP and non-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.
First-Hop Segment (FHS) Client
a Client that initiates communications with a target peer by
sending an NS message to establish reverse-path multilink
forwarding state in OMNI link intermediate nodes on the path to
the target. Note that in some arrangements the Client's (FHS)
Proxy/Server (and not the Client itself) initiates the NS.
Last-Hop Segment (LHS) Client
a Client that responds to a communications request from a source
peer's NS by returning an NA response to establish forward-path
multilink forwarding state in OMNI link intermediate nodes on the
path to the source. Note that in some arrangements the Client's
(LHS) Proxy/Server (and not the Client itself) returns the NA.
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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 routing
topology. FHS Proxy/Servers also act as intermediate forwarding
nodes to facilitate RS/RA exchanges between a Client and its Hub
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 routing topology to
the Client over that interface.
Hub Proxy/Server
a single Proxy/Server selected by a Client that injects the
Client's XLA-MNP into the BGP routing system and provides a
designated router service for all of the Client's underlay
interfaces. Clients often select the first FHS Proxy/Server they
coordinate with to serve in the Hub role (as all FHS Proxy/Servers
are equally capable candidates to serve as a Hub), however the
Client can also select any available Proxy/Server for the OMNI
link (as there is no requirement that the Hub must also be one of
the Client's FHS Proxy/Servers).
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 FHS/LHS Client pairs. The SRT maintains a
spanning tree established through BGP peerings between Gateways
and Proxy/Servers. Each SRT 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.
Mobile Node (MN)
an AERO Client and all of its downstream-attached networks that
move together as a single unit, i.e., an end system and its
connected IoT sub-networks.
Mobile Router (MR)
a MN's on-board router that forwards original IP packets/parcels
between any downstream-attached networks and the OMNI link. The
MR is the MN entity that hosts the AERO Client.
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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.
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 Hub Proxy/Server. Note that a Hub Proxy/Server can assume
the ARR role even if it is located on a different SRT segment than
the ART. The Hub Proxy/Server assumes the ARR role only when it
receives an RS message from the ART with the 'A' flag set (see:
[I-D.templin-intarea-omni]).
Potential Router List (PRL)
a geographically and/or topologically referenced list of addresses
of all Proxy/Servers within the same OMNI link. Each OMNI link
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.
AERO Forwarding Information Base (AFIB)
A forwarding table on each OAL source, destination and
intermediate node that includes AERO Forwarding Vectors (AFV) with
both multilink forwarding instructions and context for
reconstructing compressed headers for specific communicating peer
underlay interface pairs. The AFIB also supports route
optimization where one or more OAL intermediate nodes in the path
can be "skipped" to reduce path stretch and decrease load on
critical infrastructure elements.
AERO Forwarding Vector (AFV)
An AFIB entry that includes soft state (including addressing and
Identification information) for each underlay interface pairwise
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communication session between peer OAL nodes. AFVs are identified
by both a forward and reverse path AFV Index (AFVI). OAL nodes
establish reverse path AFVIs when they forward an IPv6 ND unicast
NS message and establish forward path AFVIs when they forward the
solicited IPv6 ND unicast NA response.
AERO Forwarding Vector Index (AFVI)
A locally-unique 2-octet or 4-octet value automatically generated
by an OAL node when it creates an AFV. OAL intermediate nodes
assign two distinct 4-octet AFVIs (called "A" and "B") to each
AFV, with "A" representing the forward path and "B" representing
the reverse path. Meanwhile, the OAL source assigns a single "B"
AFVI, and the OAL destination assigns a single "A" AFVI. Each OAL
node advertises its "A" AFVI to previous hop nodes on the reverse
path toward the source and advertises its "B" AFVI to next hop
nodes on the forward path toward the destination. Clients in
MANETs also assign distinct 2-octet AFVIs (called "C" and "D") to
support local multihop forwarding. The same as for the A/B AFVIs,
the "C" AFVI represents the forward path and the "D" AFVI
represents the reverse path. For unidirectional MANET paths, only
the forward path ("C") AFVI is used.
AERO Forwarding Parameters (AFP)
An OMNI option sub-option that appears in IPv6 ND NS/NA messages
and includes all parameters necessary for establishing AFV state
in OAL nodes in the path (see: [I-D.templin-intarea-omni]).
3. Requirements
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:
4.1. AERO Node Types
AERO Hosts configure an OMNI interface over an underlay interface
connected to a Client's ENET and coordinate with both other AERO
Hosts and Clients over the ENET. As an implementation matter, the
Host either assigns the same (MNP-based) IP address from the underlay
interface to the OMNI interface, or configures the "OMNI interface"
as a virtual sublayer of the underlay interface itself. AERO Hosts
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treat the ENET as an ANET, and treat the upstream Client for the ENET
as a Proxy/Server. AERO Hosts are seen as OMNI link termination
endpoints.
AERO 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 register their Mobile Network Prefixes
(MNPs) with the AERO service, and distribute the MNPs to ENETs (which
may connect AERO Hosts and other Clients). AERO Clients provide
Proxy/Server-like services for Hosts and other Clients on downstream-
attached ENETs.
AERO Gateways, Proxy/Servers and Relays are critical infrastructure
elements in fixed (i.e., non-mobile) INET deployments and hence have
permanent and unchanging INET addresses. Together, they constitute
the AERO service which provides an OMNI link virtual overlay for
connecting AERO Clients and Hosts. AERO Gateways (together with
Proxy/Servers) provide the secured backbone supporting infrastructure
for a Segment Routing Topology (SRT) spanning tree for the OMNI link.
AERO Gateways 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 also peers with Proxy/Servers
and other Gateways in a dynamic routing protocol instance to provide
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
secured tunnels with Proxy/Servers, Relays and other Gateways; they
further maintain forwarding table entries for each MNP or non-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 also peers with Gateways in
an adaptation layer dynamic routing protocol instance to advertise
its list of associated MNPs (see Section 4.2.3). Hub Proxy/Servers
provide prefix delegation/registration 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 ANET/INET boundaries provide a primary forwarding service
for ANET Clients/Host communications with peers in external INETs,
while Proxy/Servers in open INETs provide an authentication service
IPv6 ND messages but should be used only a last resort data plane
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forwarding service when a Client cannot forward directly to an INET
peer or Gateway. 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/parcels between the OMNI link and nodes
on other links/networks. Relays run a dynamic routing protocol to
discover any non-MNP prefixes in service on other 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 non-MNP prefixes
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:
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+-----------------+
| 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 )-. | AERO | | AERO | .-(_ IP )-.
(__ ENET )--|Host H1| |Host H2|--(__ ENET )
`-(______)-' +-------+ +-------+ `-(______)-'
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 Proxy/Servers (S1, S2).
Gateways provide the backbone for an SRT spanning tree for the
OMNI link.
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* 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
non-MNP 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 ENETs.
* AERO Hosts H1 and H2 attach to the ENETs served by Clients C1 and
C2, respectively.
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 L2 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.
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 OMNI Adaptation
Layer (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/parcel. An
example OMNI link SRT is shown in Figure 2:
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. . . . . . . . . . . . . . . . . . . . . . .
. .
. .-(::::::::) .
. .-(::::::::::::)-. +-+ .
. (:::: Segment A :::)--|G|---+ .
. `-(::::::::::::)-' +-+ | .
. `-(::::::)-' | .
. | .
. .-(::::::::) | .
. .-(::::::::::::)-. +-+ | .
. (:::: Segment B :::)--|G|---+ .
. `-(::::::::::::)-' +-+ | .
. `-(::::::)-' | .
. | .
. .-(::::::::) | .
. .-(::::::::::::)-. +-+ | .
. (:::: Segment C :::)--|G|---+ .
. `-(::::::::::::)-' +-+ | .
. `-(::::::)-' | .
. | .
. ..(etc).. x .
. .
. .
. <- Segment Routing Topology (SRT) -> .
. (Spanned by OMNI Link) .
. . . . . . . . . . . . . .. . . . . . . . .
Figure 2: OMNI Link Segment Routing Topology (SRT)
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 treated 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 AERO Multinet service concatenates SRT segments to form a larger
network through Gateway-to-Gateway peerings as originally suggested
in the "Catenet Model for Internetworking" [IEN48]; especially
Figure 2 follows directly from the illustrations in [IEN48-2]. The
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Catenet concept suggested a "network-of-networks" concatenation of
independent and diverse Internetwork "segments" to form a much larger
network supporting end-to-end services.
The Catenet concept first articulated in the 1970's was distorted
through the evolution of the Internet in the decades that followed,
since the adaptation layer was a critical element missing from the
architecture. As a result, while the Internet has been successful
beyond measure it has evolved as a monolithic public routing and
addressing service interconnecting private domains instead of a true
network-of-networks which has impeded flexibility and inhibited end-
to-end services. The adaptation layer manifested by AERO and OMNI
now provides the means to address these limitations as well as the
other "6 Ms of Modern Internetworking" according to the original
Catenet network-of-networks vision.
4.2.2. Addressing and Node Identification
AERO nodes on OMNI links use the Link-Local Address (LLA) prefix
fe80::/64 [RFC4291] to assign LLAs to the OMNI interface to satisfy
the requirements of [RFC4861]. AERO Clients configure LLAs
constructed from MNPs (i.e., "LLA-MNPs") while AERO infrastructure
nodes construct LLAs based on 56-bit random values ("LLA-RNDs") per
[I-D.templin-intarea-omni]. Non-MNP routes are also represented the
same as for MNPs, but may include a prefix that is not properly
covered by an MSP.
AERO nodes also use the Unique Local Address (ULA) prefix fd00::/8
followed by a pseudo-random 40-bit Global ID to form the prefix
{ULA}::/48, then include a 16-bit Subnet ID '*' to form the prefix
{ULA*}::/64 [RFC4291]. The AERO node then uses the prefix
{ULA*}::/64 to form "ULA-MNPs" or "ULA-RNDs" as specified in
[I-D.templin-intarea-omni] to support OAL addressing. (The prefix
{ULA*}::/64 appearing alone and with no suffix represents "default"
for that prefix.)
AERO Clients also use Temporary Local Addresses (TLAs) and eXtended
Local Addresses (XLAs) constructed per [I-D.templin-intarea-omni],
where TLAs are distinguished from ordinary ULAs based on the prefix
fd00::/16 and XLAs are distinguished from ULAs/TLAs based on the
prefix fd00::/64. Clients use TLA-RNDs only in initial control
message exchanges until a stable MNP is assigned, but may sometimes
also use them for sustained communications within a local routing
region. AERO nodes use XLA-MNPs to provide forwarding information
for the global routing table as well as IPv6 ND message addressing
information.
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AERO MSPs, MNPs and non-MNP routes are typically based on Global
Unicast Addresses (GUAs), but in some cases may be based on IPv4
private addresses [RFC1918] or IPv6 ULA-C's [RFC4193]. A GUA block
is also reserved for OMNI link anycast purposes. See
[I-D.templin-intarea-omni] for a full specification of LLAs, ULAs,
TLAs, XLAs, GUAs and anycast addresses used by AERO nodes on OMNI
links.
Finally, AERO Clients and Proxy/Servers configure node identification
values as specified in [I-D.templin-intarea-omni].
4.2.3. AERO Routing System
The AERO routing system comprises a private Border Gateway Protocol
(BGP) [RFC4271] service coordinated between Gateways and Proxy/
Servers (Relays also engage in the routing system as simplified
Proxy/Servers). 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 links and networks connected by Relays.
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 only for ULA prefixes for
infrastructure elements and XLA-MNPs corresponding to MNP and non-MNP
routes that are currently active; Gateways also maintain black-hole
routes for the OMNI link MSPs so that OAL packets/fragments destined
to non-existent more-specific routes are dropped with a Destination
Unreachable message returned. 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 non-
AERO links) and they forward all other OAL packets/fragments to
Gateways which have full topology knowledge.
Each OMNI link segment assigns a unique sub-prefix of {ULA}::/48
known as the "SRT prefix". For example, a first segment could assign
{ULA}:1000::/56, a second could assign {ULA}:2000::/56, a third could
assign {ULA}:3000::/56, etc. Within each segment, each Proxy/Server
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configures a ULA-RND within the segment's SRT prefix with a 56-bit
random value in the interface identifier as specified in
[I-D.templin-intarea-omni].
The administrative authorities for each segment must therefore
coordinate to assure mutually-exclusive ULA prefix assignments, but
internal provisioning of ULAs is an independent local consideration
for each administrative authority. For each ULA prefix, the
Gateway(s) that connect that segment assign the all-zero's address of
the prefix as a Subnet Router Anycast address. For example, the
Subnet Router Anycast address for {ULA}:1023::/64 is simply
{ULA}:1023::/64.
ULA prefixes are statically represented in Gateway forwarding tables.
Gateways join multiple SRT segments into a unified OMNI link over
multiple diverse network administrative domains. They support a
virtual bridging service by first establishing forwarding table
entries for their ULA prefixes either via standard BGP routing or
static routes. For example, if three Gateways ('A', 'B' and 'C')
from different segments serviced {ULA}:1000::/56, {ULA}:2000::/56 and
{ULA}:3000::/56 respectively, then the forwarding tables in each
Gateway appear as follows:
A: {ULA}:1000::/56->local, {ULA}:2000::/56->B, {ULA}:3000::/56->C
B: {ULA}:1000::/56->A, {ULA}:2000::/56->local, {ULA}:3000::/56->C
C: {ULA}:1000::/56->A, {ULA}:2000::/56->B, {ULA}:3000::/56->local
These forwarding table entries rarely change, since they correspond
to fixed infrastructure elements in their respective segments.
MNP (and non-MNP) routes are instead dynamically advertised in the
AERO routing system by Proxy/Servers and Relays that provide service
for their corresponding MNPs. The routes are advertised as XLA-MNP
prefixes, i.e., as fd00::{MNP} (see: [I-D.templin-intarea-omni]).
For example, if three Proxy/Servers ('D', 'E' and 'F') service the
MNPs 2001:db8:1000:2000::/56, 2001:db8:3000:4000::/56 and
2001:db8:5000:6000::/56 then the routing system would include:
D: fd00::2001:db8:1000:2000/120
E: fd00::2001:db8:3000:4000/120
F: fd00::2001:db8:5000:6000/120
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Note that the MNP length found in OMNI Neighbor Control sub-option
encodes a Preflen between 1 and 64, but the corresponding XLA-MNP is
entered into the routing system with length (64 + MNP length). 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 {ULA}::/48 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 ULAs,
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.
Each SRT is identified by a distinct value in the 40-bit ULA Global
ID field and assigns an OMNI IPv6 anycast address used for OMNI
interface determination in Safety-Based Multilink (SBM) as discussed
in [I-D.templin-intarea-omni]. 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 ULA 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
IPv6 ND messages.
Note: The distinct ULA 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 ULAs of multiple OMNI links within a
common routing system may be acceptable.
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4.2.5. Segment Routing For OMNI Link Selection
Original IPv6 sources can direct IPv6 packets/parcels to an AERO node
by including a standard IPv6 Segment Routing Header (SRH) [RFC8754]
with the OMNI IPv6 anycast address for the selected OMNI link as
either the IPv6 destination or as an intermediate hop within the SRH.
This allows the original source to determine the specific OMNI link
SRT an original IPv6 packet/parcel will traverse when there may be
multiple alternatives.
When an AERO node processes the SRH and forwards the original IPv6
packet/parcel to the correct OMNI interface, the OMNI interface
writes the next IPv6 address from the SRH into the IPv6 destination
address and decrements Segments Left. If decrementing would cause
Segments Left to become 0, the OMNI interface deletes the SRH before
forwarding. This form of Segment Routing supports Safety-Based
Multilink (SBM).
4.3. OMNI Interface Characteristics
OMNI interfaces are virtual interfaces configured over one or more
underlay interfaces classified as follows:
* ANET interfaces connect to a protected and secured ANET that is
separated from open INETs by Proxy/Servers. The 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 an ANET and may require NAT
traversal on the path to the Proxy/Server the same as for the INET
case.)
* 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
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.
* ENET interfaces connect a Client's downstream-attached networks,
where the Client provides forwarding services for ENET Host and
Client communications to remote peers. An ENET 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.
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* VPNed interfaces use security encapsulation over an underlay
network to a Client or Proxy/Server acting as a Virtual Private
Network (VPN) gateway. Other than the link layer encapsulation
format, VPNed interfaces behave the same as for Direct interfaces.
* Direct (aka "point-to-point") interfaces connect directly to a
Client or Proxy/Server without engaging any forwarding devices in
the path. An example is a line-of-sight link between a remote
pilot and an unmanned aircraft.
OMNI interfaces use OAL encapsulation and fragmentation as discussed
in Section 4.6. OMNI interfaces use L2 encapsulation (see:
Section 4.6) to exchange carrier packets with OMNI link neighbors
over INET or VPNed interfaces as well as over ANET interfaces for
which the Client and FHS Proxy/Server may be multiple IP hops away.
OMNI interfaces use link layer encapsulation only (i.e., and no other
L2 encapsulations) over Direct underlay interfaces or ANET interfaces
when the Client and FHS Proxy/Server are known to be on the same
underlay link.
OMNI interfaces maintain a neighbor cache for tracking per-neighbor
state the same as for any interface. OMNI interfaces use IPv6 ND
messages including Router Solicitation (RS), Router Advertisement
(RA), Neighbor Solicitation (NS), Neighbor Advertisement (NA)
unsolicited Neighbor Advertisement (uNA) and Redirect for neighbor
cache management. In environments where spoofing may be a threat,
OMNI neighbors should invoke OAL Identification window
synchronization in their IPv6 ND message exchanges.
OMNI interfaces send IPv6 ND messages with an OMNI option formatted
as specified in [I-D.templin-intarea-omni]. The OMNI option includes
prefix registration information, Interface Attributes and/or AERO
Forwarding Parameters (AFPs) containing link information parameters
for the OMNI interface's underlay interfaces and any other per-
neighbor information.
A Host's OMNI interface is configured over an underlay interface
connected to an ENET provided by an upstream Client. From the Host's
perspective, the ENET appears as an ANET and the upstream Client
appears as a Proxy/Server. The Host does not provide OMNI
intermediate node services and is therefore a logical termination
point for the OMNI link.
A Client's OMNI interface may be configured over multiple ANET/INET
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
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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 ANET/INET underlay interfaces are used "one at
a time" (i.e., all other interfaces are in standby mode while one
interface is active), then successive IPv6 ND messages all include
OMNI option Interface Attributes, Traffic Selector and/or AFP 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 link layer address.
If the Client has multiple active ANET/INET underlay interfaces, then
from the perspective of IPv6 ND it would appear to have multiple link
layer addresses. In that case, IPv6 ND message OMNI options MAY
include sub-options with different underlay interface ifIndexes.
Proxy/Servers on the open Internet include only a single INET
underlay interface. INET Clients therefore discover only the L2ADDR
information for the Proxy/Server's INET interface. Proxy/Servers on
an ANET/INET boundary include both an ANET and INET underlay
interface. ANET Clients therefore must discover both the ANET and
INET L2ADDR information for their Proxy/Servers.
Gateway and Proxy/Server OMNI interfaces are configured over underlay
interfaces that provide both secured tunnels for carrying IPv6 ND and
BGP protocol control plane messages and open INET access for carrying
unsecured messages. The OMNI interface configures a ULA-RND and acts
as an OAL source to encapsulate original IP packets/parcels, then
fragments the resulting OAL packets, performs L2 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 ULA-RND source and destination addresses. The
ULA-RND addresses that appear in the original IP packets/parcels of a
BGP protocol session may therefore be the same as those that appear
in the OAL IPv6 encapsulation header.
4.4. OMNI Interface Initialization
AERO Proxy/Servers, Clients and Hosts 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/parcels with
destination addresses covered by an MNP not explicitly associated
with another interface are directed to an OMNI interface.
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OMNI interface initialization procedures for Proxy/Servers, Clients
Hosts and Gateways are discussed in the following sections.
4.4.1. AERO Proxy/Server and Relay Behavior
When a Proxy/Server enables an OMNI interface, it assigns a ULA-RND
appropriate for the given OMNI link SRT segment. The Proxy/Server
also configures secured underlay interface tunnels and engages in 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 sending
carrier packets to OMNI interface neighbors over underlay interfaces
and/or secured tunnels. The Proxy/Server further configures a
service to facilitate IPv6 ND exchanges with AERO Clients and manages
per-Client neighbor cache entries 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 INET/ENET
interfaces (see: Section 4.2.3). The Relay provisions MNPs to
networks on the INET/ENET interfaces (i.e., the same as a Client
would do) and advertises the MSP(s) for the OMNI link over the INET/
ENET interfaces. The Relay further provides an OMNI link attachment
point for non-MNP-based topologies.
4.4.2. AERO Client Behavior
When a Client enables an OMNI interface, it assigns either an XLA-MNP
or a TLA and sends OMNI-encapsulated RS messages over its ANET/INET
underlay interfaces to an FHS Proxy/Server, which coordinates with a
Hub Proxy/Server that returns an RA message with corresponding
parameters. The RS/RA messages may pass through one or more NATs in
the path between the Client and FHS Proxy/Server. (Note: if the
Client used a TLA in its initial RS messages, it may discover ULA-
MNPs in the corresponding RAs that it receives from FHS Proxy/Servers
and begin using these new addresses. If the Client is operating
outside the context of AERO infrastructure such as in a Mobile Ad-hoc
Network (MANET), however, it may continue using TLAs for Client-to-
Client communications at least until it encounters an infrastructure
element that can delegate MNPs.)
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A Client can further extend the OMNI link over its (downstream) ENET
interfaces where it provides a first-hop router for Hosts and other
AERO Clients connected to the ENET. A downstream Client that
connects via the ENET serviced by an upstream Client can in turn
service further downstream ENETs that connect other Hosts and
Clients. This OMNI link extension can be applied recursively over a
"chain" of ENET Clients.
4.4.3. AERO Host Behavior
When a Host enables an OMNI interface, it assigns an address taken
from the ENET underlay interface which may itself be a GUA delegated
by the upstream Client. The Host does not assign a link-local
address to the OMNI interface, since no autoconfiguration is
necessary on that interface. (As an implementation matter, the Host
could instead configure the "OMNI interface" as a virtual sublayer of
the ENET underlay interface itself.)
The Host sends OMNI-encapsulated RS messages over its ENET underlay
interface to the upstream Client, which returns encapsulated RAs and
provides routing services in the same fashion that Proxy/Servers
provides services for Clients. Hosts represent the leaf end systems
in recursively-nested chain of concatenated ENETs, i.e., they
represent terminating endpoints for the OMNI link.
4.4.4. AERO Gateway Behavior
AERO Gateways configure an OMNI interface and assign a ULA-RND and
corresponding Subnet Router Anycast address for each of their OMNI
link SRT segments. 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 a
BGP routing protocol session with neighbors over the secured spanning
tree (see: Section 4.2.3).
4.5. OMNI Interface Neighbor Cache Maintenance
Each Client, Proxy/Server and Gateway OMNI interface maintains a
network layer conceptual neighbor cache per [RFC1256] or [RFC4861]
the same as for any IP interface. The OMNI interface network layer
neighbor cache is maintained through static and/or dynamic neighbor
cache entry configurations.
Each OMNI interface also maintains a separate internal adaptation
layer conceptual neighbor cache that includes a Neighbor Cache Entry
(NCE) for each of its active OAL neighbors per [RFC4861]. Throughout
this document, the terms "neighbor cache" and "NCE" refer to this
adaptation layer neighbor cache unless otherwise specified.
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Each OMNI interface NCE is indexed by the ULA of a neighbor found in
the ND message IPv6 header 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 NS/NA message
exchanges.
Hosts maintain NCEs for Clients and other Hosts through the exchange
of RS/RA, NS/NA or Redirect messages. Each NCE is indexed by the IP
address assigned to the Host ENET interface, which is the same
address used for L2 encapsulation (i.e., without the insertion of an
OAL header). This encapsulation format identifies the NCE as a Host-
based entry where the Host is a leaf end system in the recursively
extended OMNI link.
Gateways maintain NCEs for Clients within their local segments based
on NS/NA route optimization messaging (see: Section 4.13.4). When a
Gateway creates/updates a NCE for a local segment Client based on NS/
NA route optimization, it also maintains AFIB state for messages
destined to this local segment Client.
Clients establish NCEs for their associated FHS and Hub Proxy/Servers
through the exchange of RS/RA messages. When a Client and Proxy/
Server establish NCEs, they set a ReachableTime timer to
REACHABLE_TIME seconds. Clients determine the service profiles for
their FHS and Hub Proxy/Servers by setting the NUD/ARR/RPT flags in
RS messages and also by setting/clearing the FMT-Forward and FMT-Mode
flags in the Interface Attributes sub-option. When the NUD/ARR/RPT
flags are clear, Proxy/Servers forward all NS/NA messages to the
Client, while the Client performs mobility update signaling through
the transmission of uNA messages to all active neighbors following a
mobility event. However, in some environments this may result in
excessive NS/NA control message overhead especially for Clients
connected to low-end data links.
Clients can therefore set the NUD/ARR/RPT flags in RS messages they
send to select their Proxy/Server service profiles. If the NUD flag
is set, the FHS Proxy/Server that forwards the RS message assumes the
role of responding to NS messages and maintains peer NCEs associated
with the NCE for this Client. If the ARR flag is set, the Hub Proxy/
Server that processes the RS message assumes the role of responding
to NS(AR) messages on behalf of this Client NCE. If the RPT flag is
set, the Hub Proxy/Server that processes the RS message becomes
responsible for maintaining a "Report List" for each Client NCE for
the source addresses of NS(AR) messages it forwards on behalf of this
Client.
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When a Client sets the RPT flag, the Hub Proxy/Server maintains
Report List entries based on a ReportTime timer initialized to
REACHABLE_TIME seconds upon receipt of an NS(AR) and decremented once
per second while no additional NS(AR)s arrive. The Hub Proxy/Server
then sends uNA messages to each Report List entry when it receives a
Client mobility update indication (e.g., through receipt of an RS
with updated Interface Attributes and/or Traffic Selectors). When a
Report List entry ReportTime timer expires, the Hub Proxy/Server
deletes the entry. When a Client NCE timer expires, the Hub Proxy/
Server deletes the NCE along with its associated Report List.
Clients can also set/clear the FMT-Forward and FMT-Mode flags in the
Interface Attributes sub-option of each RS message to express their
desired service profile from each FHS Proxy/Server. The FHS Proxy/
Server will consider the Client's preferences and either accept or
override by setting/clearing the flags in the corresponding RA
message reply. Implications for these bits are discussed in
[I-D.templin-intarea-omni].
Both the Client and its Hub 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. Clients
determine their FHS and Hub Proxy/Server service models by setting
the NUD/ARR/RPT flags in the RS messages they send as discussed
above.
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 Hub Proxy/Server for the ART.
The Hub 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 a NCE for the ART while caching L3 and
L2 addressing information. The ARS then (re)sets ReachableTime for
the NCE to REACHABLE_TIME seconds and performs unicast NS/NA
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 NA messages
arrive.
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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 IPv6 ND 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/Hub 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.
AERO nodes also use the value MAX_UNICAST_SOLICIT to limit the number
of NS 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 uNAs 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. OMNI ND Messages
OMNI interfaces prepare IPv6 ND messages the same as for standard
IPv6 ND, but also include a new option type termed the OMNI option
[I-D.templin-intarea-omni]. OMNI interfaces use ULAs instead of LLAs
as IPv6 ND message source and destination addresses. This allows
multiple different OMNI links to be joined into a single link at some
future time without requiring a global renumbering event.
For each IPv6 ND message, the OMNI interface includes one or more
OMNI options (and any other ND message options) then completely
populates all option information. If the OMNI interface includes an
authentication option, it first writes the value 0 into the
authentication signature field then calculates the signature
beginning with the first IPv6 ND message octet following the header
Checksum field and continuing over the entire length of the packet or
super-packet. The OMNI interface next writes the authentication
signature value into the appropriate OMNI authentication option
field, then calculates the IPv6 ND message checksum per [RFC4443]
beginning with a pseudo-header of the IPv6 header and writes the
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value into the Checksum field. The IPv6 ND message checksum
therefore provides integrity assurance for the message, while the
authentication signature covers the entire packet or super-packet.
OMNI interfaces verify integrity and authentication of each packet or
super-packet received, and process the message further only following
successful verification.
OMNI options include per-neighbor information that provides multilink
forwarding, link layer address and traffic selector information for
the neighbor's underlay interfaces. This information is stored in
both the neighbor cache and AERO Forwarding 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.
The OMNI option is distinct from any Source/Target Link-Layer Address
Options (S/TLLAOs) that may appear in an IPv6 ND message according to
the appropriate IPv6 over specific link layer specification (e.g.,
[RFC2464]). If both OMNI options and S/TLLAOs appear, the former
pertains to adaptation layer to underlay interface address mappings
while the latter pertains to the native L2 address format of the
underlay media.
OMNI interface IPv6 ND messages may also include other IPv6 ND
options. In particular, solicitation messages may include a Nonce
option if required for verification of advertisement replies. If an
OMNI IPv6 ND solicitation message includes a Nonce option, the
advertisement reply must echo the same Nonce. If an OMNI IPv6 ND
solicitation message includes a Timestamp option, the recipient must
also include a Timestamp option in its advertisement reply. All
unsolicited advertisement and redirect messages should include a
Timestamp option.
AERO Clients send RS messages to the link-scoped All-Routers
multicast address or a ULA-RND while using unicast or anycast OAL/L2
addresses. AERO Proxy/Servers respond by returning unicast RA
messages. During the RS/RA exchange, AERO Clients and Proxy/Servers
include state synchronization parameters to establish Identification
windows and other state.
AERO Hosts and Clients on ENET underlay networks send RS messages to
the link-scoped All-Routers multicast address, a ULA-RND of a remote
Hub Proxy/Server or the ULA-MNP of an upstream Client while using
unicast or anycast OAL/L2 addresses. The upstream AERO Client
responds by returning a unicast RA message.
AERO nodes use NS/NA messages for the following purposes:
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* NS/NA(AR) messages are used for address resolution and optionally
to establish sequence number windows. The ARS sends an NS(AR) to
the solicited-node multicast address of the ART, and an ARR with
addressing information for the ART returns a unicast NA(AR) that
contains current, consistent and authentic target address
resolution information. NS(AR) messages include a solicited-node
multicast destination address to distinguish them from ordinary NS
messages. NS/NA(AR) messages must be secured.
* Ordinary NS/NA messages are used determine target reachability,
establish and maintain NAT state, and/or establish AFIB state.
The source sends an NS to the unicast address of the target while
optionally including an OMNI AERO Forwarding Parameters (AFP) sub-
option naming a specific underlay interface pair, and the target
returns a unicast NA that includes a responsive AFP if necessary.
NS/NA messages that use an in-window sequence number and do not
update any other state need not include an authentication
signature but must include an IPv6 ND message checksum. NS/NA
messages used to establish window synchronization and/or AFIB
state must be secured.
* Unsolicited NA (uNA) messages are used to signal addressing and/or
other neighbor state changes (e.g., address changes due to
mobility, signal degradation, traffic selector updates, etc.). uNA
messages can also be also used to acknowledge receipt of non-
solicitation IPv6 ND messages (see below). uNA messages that
update state information must be secured.
* NS/NA(DAD) messages are not used in AERO, since Duplicate Address
Detection is not required.
AERO and OMNI together support an added reliability feature not
available in ordinary IPv6 ND messaging. In particular, nodes can
set the OMNI Neighbor Coordination SNR flag or Window Synchronization
SYN flag in unicast non-solicitation IPv6 ND messages (including RA,
NA and Redirect) to request a synchronous (but "unsolicited") uNA
response (see: [I-D.templin-intarea-omni]).
The node that processes an SNR/SYN message prepares the response the
same as for an ordinary uNA as specified in [RFC4861], including the
setting of the R/S/O flags as discussed below. The node sets the uNA
Target Address to the unicast destination and uNA destination address
to the unicast source of the original message.
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The node then sets the uNA source address to its own address and
includes any necessary OMNI sub-options but MUST NOT itself set the
SNR/SYN flags. If the SNR/SYN message included a Nonce and/or
Timestamp option, the node includes matching Nonce/Timestamp options
in the uNA response. The node finally returns the uNA message to the
source of the SNR/SYN message.
4.5.2. OMNI Neighbor Advertisement Message Flags
As discussed in Section 4.4 of [RFC4861] NA messages include three
flag bits R, S and O. OMNI interface NA messages treat the flags as
follows:
* R: The R ("Router") flag is set to 1 in the NA messages sent by
all AERO forwarding nodes on the OMNI link. (AERO Hosts are by
definition the only non-forwarding nodes on the OMNI link and
therefore set the R flag to 0.)
* S: The S ("Solicited") flag is set exactly as specified in
Section 4.4. of [RFC4861], i.e., it is set to 1 for Solicited NAs
and set to 0 for uNAs (both unicast and multicast).
* O: The O ("Override") flag is set to 0 for solicited NAs returned
by a Proxy/Server ARR and set to 1 for all other solicited and
unsolicited NAs. For further study is whether solicited NAs for
anycast targets apply for OMNI links. Since XLA-MNPs must be
uniquely assigned to Clients to support correct IPv6 ND protocol
operation, however, no role is currently seen for assigning the
same XLA-MNP to multiple Clients.
4.5.3. 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 OAL packets using randomly-
initialized and monotonically-increasing Identification values
(modulo 2**32) without window synchronization. In environments where
spoofing is considered a threat, OMNI interface neighbors instead
invoke window synchronization by including OMNI Window
Synchronization sub-options in RS/RA or NS/NA message exchanges to
maintain send/receive window state in their respective neighbor cache
and AFIB entries as specified in [I-D.templin-intarea-omni].
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4.6. OMNI Interface Encapsulation and Fragmentation
When the network layer forwards an original IP packet/parcel into an
OMNI interface, the interface locates or creates a Neighbor Cache
Entry (NCE) that matches the destination. The OMNI interface then
invokes the OMNI Adaptation Layer (OAL) as discussed in
[I-D.templin-intarea-omni] which encapsulates the packet/parcel in an
IPv6 header to produce an OAL packet. For example, an original IP
packet/parcel with source address 2001:db8:1:2::1 and destination
address 2001:db8:1234:5678::1 might cause the OAL encapsulation
header to include source address {XLA*}::2001:db8:1:2 (i.e., an XLA-
MNP) and destination address {ULA*}::0012:3456:789a:bcde (i.e., a
ULA-RND).
Following encapsulation, the OAL source then calculates a 2-octet OAL
checksum, then fragments the OAL packet while including an identical
Identification value for each fragment that must be within the window
for the neighbor. The OAL source then appends the checksum as the
final 2 octets of the final fragment, i.e., as a "trailer".
The OAL source next includes an identical Compressed Routing Header
with 32-bit ID fields (CRH-32) [I-D.bonica-6man-comp-rtg-hdr] with
each fragment containing AERO Forwarding Vector Indexes (AFVIs) as
discussed in Section 4.13. The OAL source can instead invoke OAL
header compression by replacing the OAL IPv6 header, CRH-32 and
Fragment Header with an OAL Compressed Header (OCH).
The OAL source finally encapsulates each resulting OAL fragment in L2
headers to form a carrier packet, with source address set to its own
L2 address (e.g., 192.0.2.100) and destination set to the L2 address
of the next hop OAL intermediate node or destination (e.g.,
192.0.2.1). The carrier packet encapsulation format in the above
example is shown in Figure 3:
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| L2 Headers |
~ src = 192.0.2.100 ~
| dst = 192.0.2.1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OAL IPv6 Header |
~ src = {XLA*}::2001:db8:1:2 ~
|dst={ULA*}::0012:3456:789a:bcde|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ CRH-32 (if necessary) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ OAL Fragment Header ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Original IP Header |
~ (first-fragment only) ~
~ src = 2001:db8:1:2::1 ~
| dst = 2001:db8:1234:5678::1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ ~
~ Original Packet Body/Fragment ~
~ ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OAL Checksum | <-- (final-fragment only)
+-+-+-+-+-+-+-+-+
Figure 3: Carrier Packet Format
(Note that carrier packets exchanged by Hosts on ENETs do not include
the OAL IPv6 or CRH-32 headers, i.e., the OAL encapsulation is NULL
and only the Fragment Header and L2 encapsulations are included.)
In this format, the OAL source encapsulates the original IP header
and packet/parcel body/fragment in an OAL IPv6 header prepared
according to [RFC2473], the CRH-32 is a Routing Header extension of
the OAL header, the Fragment Header identifies each fragment, and the
L2 headers are prepared as discussed in [I-D.templin-intarea-omni].
The OAL source sends each such carrier packet into the SRT spanning
tree, where they are forwarded over possibly multiple OAL
intermediate nodes until they arrive at the OAL destination.
The OMNI link control plane service distributes Client XLA-MNP prefix
information that may change occasionally due to regional node
mobility, as well as XLA-MNP prefix information for Relay non-MNPs
and per-segment ULA prefix information that rarely changes. OMNI
link Gateways and Proxy/Servers use the information to establish and
maintain a forwarding plane spanning tree that connects all nodes on
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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 Forwarding
Information Base (AFIB) that caches AERO Forwarding 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 to greatly improve performance and
reduce load on critical infrastructure elements.
For OAL packets/fragments undergoing L2 re-encapsulation at an OAL
intermediate node, the OMNI interface removes the L2 encapsulation
headers and reassembles 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, recalculates the OAL checksum and re-fragments if
necessary, then re-encapsulates each fragment in new L2 encapsulation
headers to form carrier packets appropriate for next segment
forwarding.
When an FHS Gateway forwards an OAL packet/fragment to an LHS Gateway
over the unsecured spanning tree, it reconstructs the OAL header
based on AFV state, inserts a CRH-32 immediately following the OAL
header and adjusts the OAL payload length and destination address
field. The FHS Gateway includes a single AFVI in the CRH-32 that the
LHS Gateway can use to search its AFIB, then forwards the OAL packet/
fragment over the unsecured spanning tree. When the LHS Gateway
receives the OAL packet/fragment, it locates the AFV for the next hop
based on the CRH-32 AFVI then re-applies header compression
(resulting in the removal of the CRH-32) and forwards the OAL packet/
fragment to the next hop.
4.7. OMNI Interface Decapsulation
When an OAL node receives OAL packets/fragments addressed to another
node, it discards the L2 headers and includes new L2 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.
When an OAL node receives OAL packets/fragments addressed to itself,
it discards the L2 headers, verifies the Identification, reassembles
to obtain the original OAL packet (or super-packet - see:
[I-D.templin-intarea-omni]) then finally verifies the OAL checksum.
Next, if the enclosed original IP packet(s)/parcel(s) are destined
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either to itself or to a destination reached via an interface other
than the OMNI interface, the OAL node discards the OAL encapsulation
and forwards the original IP packet(s)/parcel(s) to the network
layer.
If the original IP packet(s)/parcel(s) are destined to another node
reached by the OMNI interface, the OAL node instead changes the OAL
source to its own address, changes the OAL destination to the ULA of
the next-hop node over the OMNI interface, decrements the Hop Limit,
recalculates the OAL checksum, refragments if necessary, includes new
L2 headers appropriate for the next hop, then sends these new carrier
packets into the next hop underlay interface.
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/parcels that originate from within the same secured
ANET.
* AERO Clients and Relays accept original IP packets/parcels from
downstream network correspondents based on ingress filtering.
* AERO Hosts, Clients, Relays, Proxy/Servers and Gateways verify
carrier packet L2 encapsulation addresses according to
[I-D.templin-intarea-omni].
* AERO nodes 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/parcels 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), Maximum Reassembly Unit (MRU) and
the role of fragmentation and reassembly [I-D.ietf-intarea-tunnels].
The OMNI interface employs an OMNI Adaptation Layer (OAL) that
accommodates multiple underlay links with diverse MTUs while
observing both a minimum and per-path Maximum Payload Size (MPS).
OMNI interface packet sizing considerations are specified in
[I-D.templin-intarea-omni], where the OMNI interface MTU can
essentially be considered "unlimited".
When the network layer presents an original IP packet/parcel to the
OMNI interface, the OAL source encapsulates and fragments the packet/
parcel if necessary. When the network layer presents the OMNI
interface with multiple original IP packets/parcels bound to the same
OAL destination, the OAL source can concatenate them as a single OAL
super-packet as discussed in [I-D.templin-intarea-omni] before
applying fragmentation. The OAL source then encapsulates each OAL
fragment in L2 headers for transmission as carrier packets over 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 (see the definition of link in [RFC8200]).
Note: Although a CRH-32 may be inserted or removed by a Gateway in
the path (see: Section 4.10.4), this does not interfere with the
destination's ability to reassemble since the CRH-32 is not included
in the fragmentable part and its removal/transformation does not
invalidate fragment header information.
4.10. OMNI Interface Forwarding Algorithm
Original IP packets/parcels 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 link layer
(i.e., from an OMNI interface neighbor). All original IP packets/
parcels 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/parcels 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/parcel should instead be
forwarded back to the network layer, the packet/parcel is dropped to
avoid looping). Carrier packets that enter the OMNI interface from
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the link layer are either re-encapsulated and re-admitted into the
link layer, or reassembled and forwarded to the network layer where
they are subject to either local delivery or IP forwarding.
When the network layer forwards an original IP packet/parcel into the
OMNI interface, it decrements the TTL/Hop Limit following standard IP
router conventions. Once inside the OMNI interface, however, the OAL
does not further decrement the original IP packet/parcel TTL/Hop
Limit since its adaptation layer forwarding actions occur below the
network layer. The original IP packet/parcel'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 node receives a carrier packet, it discards
the L2 headers to obtain the enclosed OAL packet/fragment. When the
intermediate node forwards an OAL packet/fragment not addressed to
itself, 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 node drops the OAL
packet/fragment. This ensures that original IP packet(s)/parcel(s)
cannot enter an endless loop.
OMNI interfaces may have multiple underlay interfaces and/or neighbor
cache entries 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 segment routing and/or link layer
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 may improve 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 only use "reachable" interfaces for
forwarding purposes.
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
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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.
The ULA Subnet ID value is used only for subnet coordination within a
local OMNI link segment. When a node forwards an OAL packet/fragment
addressed to a ULA with a foreign Global and/or Subnet ID value, it
forwards the OAL packet/fragment based solely on the OMNI link
routing information. For this reason, OMNI link routing and
forwarding table entries always include both ULA-RNDs with their
associated prefix lengths and XLA-MNPs which encode an MNP while
leaving the Global and Subnet ID values set to 0.
The following sections discuss the OMNI interface-specific forwarding
algorithms for Hosts, Clients, Proxy/Servers and Gateways. In the
following discussion, an original IP packet/parcel's destination
address is said to "match" if it is the same as a cached address, or
if it is covered by a cached prefix (which may be encoded in an
{ULA,XLA}-MNP).
4.10.1. Host Forwarding Algorithm
When an original IP packet/parcel enters a Host's OMNI interface from
the network layer the Host searches for a NCE that matches the
destination. If there is a matching NCE, the Host performs OMNI L2
encapsulation, fragments if necessary as discussed in Section 6.13 of
[I-D.templin-intarea-omni] then sends the resulting carrier packets
into the ENET addressed to the L2 address of the neighbor. If there
is no match, the host instead sends the carrier packets to its
upstream Client.
After sending the carrier packet, the Host may receive an OAL
Redirect message from its upstream Client to inform it of another
AERO node on the same ENET that would provide a better first hop.
The Host authenticates the Redirect message, then updates its
neighbor cache accordingly.
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4.10.2. Client Forwarding Algorithm
When an original IP packet/parcel enters a Client's OMNI interface
from the network layer the Client searches for a NCE that matches the
destination. If there is a matching NCE for a neighbor reached via
an ANET/INET interface (i.e., an upstream interface), the Client
selects one or more "reachable" neighbor interfaces in the entry for
forwarding purposes. Otherwise, the Client performs OAL
encapsulation and fragmentation, forwards the resulting OAL packet/
fragment to an FHS Proxy/Server, then either invokes address
resolution and multilink forwarding procedures per Section 4.13 or
allows the FHS Proxy/Server to invoke these procedures on its behalf.
If there is a matching NCE for a neighbor reached via an ENET
interface (i.e., a downstream interface), the Client instead forwards
the original IP packet/parcel to the downstream Host or Client using
encapsulation and fragmentation if necessary.
When a carrier packet enters a Client's OMNI interface from the link
layer, the Client discards the L2 headers to obtain the OAL packet/
fragment then examines the OAL destination. If the OAL destination
matches one of the Client's ULAs 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/parcel to the network layer. If the OAL
destination matches a NCE for a peer Client on an ENET interface, the
Client instead forwards the OAL packet/fragment to the peer while
decrementing the OAL Hop Limit. If the OAL destination matches a NCE
for a Host on an ENET interface, the Client instead reassembles then
forwards the original IP packet/parcel to the Host while using L2
encapsulation and fragmentation (i.e., without invoking the OAL) if
necessary. If the OAL destination does not match, the Client drops
the original IP packet/parcel and MAY return a network layer ICMP
Destination Unreachable message subject to rate limiting (see:
Section 4.11).
When a Client forwards an OAL packet/fragment from an ENET Host to a
neighbor connected to the same ENET, it also returns a Redirect
message to inform the Host that it can reach the neighbor directly as
an ENET peer.
Note: Clients and their FHS Proxy/Server (and other Client) peers can
exchange original IP packets/parcels over ANET underlay interfaces
using OMNI L2 encapsulation without invoking the OAL, since the ANET
is secured at the link and physical layers. By forwarding original
IP packets/parcels without invoking the OAL, the ANET peers use the
same L2 encapsulation and fragmentation procedures as specified for
Hosts above.
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Note: The forwarding table entries established in peer Clients of a
multihop forwarding region are based on ULA-MNPs and/or TLAs used to
seed the multihop routing protocols. When ULA-MNPs are used, the ULA
/64 prefix provides topological relevance for the multihop forwarding
region, while the 64-bit Interface Identifier encodes the Client MNP.
Therefore, Clients can forward atomic fragments with compressed OAL
headers that do not include ULA or AFVI information by examining the
MNP-based addresses in the original IP packet/parcel header. In
other words, each forwarding table entry contains two pieces of
forwarding information - the ULA information in the prefix and the
MNP information in the interface identifier.
4.10.3. Proxy/Server and Relay Forwarding Algorithm
When the network layer admits an original IP packet/parcel into a
Proxy/Server's OMNI interface, the OAL drops the packet/parcel 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 ULA of a
neighboring Gateway found in the OMNI interface's network layer
neighbor cache. If so, the Proxy/Server performs OAL fragmentation
followed by L2 encapsulation then sends the resulting carrier packets
to the neighboring Gateway over a secured tunnel to support the
operation of the BGP routing protocol. If the destination is a non-
ULA, the Proxy/Server instead assumes the Relay role and forwards the
original IP packet/parcel in a similar manner as for Clients.
Specifically, if there is a matching NCE the Proxy/Server selects one
or more "reachable" neighbor interfaces in the entry for forwarding
purposes; otherwise, the Proxy/Server performs OAL encapsulation/
fragmentation followed by L2 encapsulation and sends 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 delegated MNP, the
Proxy/Server drops the carrier packets regardless of their OMNI link
point of origin. The Proxy/Server also drops original IP packets/
parcels received on underlay interfaces either directly from an ANET
Client or following reassembly of carrier packets received from an
ANET/INET Client if the original IP destination corresponds to the
same Client's delegated MNP. Proxy/Servers also drop carrier packets
that contain OAL packets/fragments with foreign OAL destinations that
do not match their own ULA, the ULA of one of their Clients or a ULA
corresponding to one of their GUA routes. These checks are essential
to prevent forwarding inconsistencies from accidentally or
intentionally establishing endless loops that could congest nodes
and/or ANET/INET links.
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Proxy/Servers process carrier packets that contain OAL packets/
fragments with OCH headers or with destinations that match their ULA
and also include a CRH-32 header that encodes AFVI information. The
Proxy/Server examines the AFVI to locate the corresponding AFV entry
in the AFIB. If the carrier packets were not received from the
secured spanning tree, the Proxy/Server must then verify that the L2
addresses are "trusted" according to the AFV. If the carrier packets
were trusted, the Proxy/Server then forwards them according to the
AFV state while decrementing the OAL packet/fragment Hop Limit.
For OAL packets/fragments with destinations that match their ULA but
do not include a CRH-32/OCH, the Proxy/Server instead discards the L2
headers and performs OAL reassembly if necessary to obtain the
original IP packet/parcel. For data packets/parcels addressed to
their own ULA that arrived via the secured spanning tree, the Proxy/
Server delivers the original IP packet/parcel to the network layer to
support secured BGP routing protocol control messaging. For data
packets/parcels originating from one of its dependent Clients, the
Proxy/Server instead performs OAL encapsulation/fragmentation then
performs L2 encapsulation and sends the resulting carrier packets
while invoking address resolution and multilink forwarding procedures
per Section 4.13. For IPv6 ND 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.
When the Proxy/Server receives a carrier packet that contains an OAL
packet/fragment with OAL destination set to a {ULA,XLA}-MNP of one of
its Client neighbors established through RS/RA exchanges, it accepts
the carrier packet only if data origin authentication succeeds. If
the NCE state is DEPARTED, the Proxy/Server changes the OAL
destination address to the ULA of the new Proxy/Server, decrements
the OAL Hop Limit, then supplies new OMNI L2 headers and forwards the
resulting carrier packet into the spanning tree which will eventually
deliver it to the new Proxy/Server. If the neighbor cache state for
the Client is REACHABLE and the Proxy/Server is a Hub responsible for
serving as the Client's address resolution responder and/or default
router, it submits the OAL packet/fragment for reassembly then
decapsulates and processes the resulting IPv6 ND message or original
IP packet/parcel accordingly. Otherwise, the Proxy/Server decrements
the OAL Hop Limit, supplies new OMNI L2 headers and sends the carrier
packets to the Client which must then perform data origin
verification and reassembly. (In the latter case, the Client may
receive fragments of the same original IP packet/parcel from
different Proxy/Servers but this will not interfere with reassembly.)
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When the Proxy/Server receives a carrier packet that contains an OAL
packet/fragment with OAL destination set to a {ULA,XLA}-MNP that does
not match the MSP, it accepts the carrier packet only if data origin
authentication succeeds and if there is a network layer forwarding
table entry for a GUA route that matches the MNP. The Proxy/Server
then discards the L2 headers, performs OAL reassembly and
decapsulation to obtain the original IP packet/parcel, then presents
it to the network layer (as a Relay) where it will be delivered
according to standard IP forwarding.
Clients and their FHS Proxy/Server peers can exchange original IP
packets/parcels over ANET underlay interfaces using L2 encapsulation
with Type-3 compressed OAL headers that include only fragmentation
information and no OAL addressing information, since the ANET is
secured at the link and physical layers. (For packets that do not
require fragmentation, the peers can even omit the Type-3 header.)
FHS Proxy/Servers will then supply a Type 0/1/2 OAL header when they
forward ANET Client original IP packets/parcels toward final
destinations located in other networks.
Proxy/Servers forward OAL packets/fragments received in secure
control plane carrier packets via the SRT secured spanning tree and
forward other OAL packets/fragments via the unsecured spanning tree.
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. When a
Proxy/Server receives a carrier packet from the unsecured spanning
tree, it applies data origin authentication itself and/or forwards
the enclosed unsecured OAL contents toward the destination which must
apply data origin authentication on its own behalf.
If the Proxy/Server has multiple original IP packets/parcels to send
to the same neighbor, it can concatenate them as a single OAL super-
packet [I-D.templin-intarea-omni]. If the super-packet begins with
an IPv6 ND control message to be sent over the secured spanning tree,
the remainder of the super-packet also traverses the secured spanning
tree.
4.10.4. Gateway Forwarding Algorithm
When the network layer admits an original IP packet/parcel 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 ULA of a neighboring Gateway
or Proxy/Server by examining the OMNI interface's network layer
neighbor cache. If so, the Gateway performs OAL fragmentation
followed by L2 encapsulation and forwards the resulting carrier
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packets to the neighboring Gateway or Proxy/Server over a secured
tunnel to support the operation of the BGP routing protocol between
OAL neighbors.
Gateways forward OAL packets/fragments received in 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 IPv6 ND control messages
or BGP routing protocol 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 removes the L2 headers
to obtain the OAL packet/fragment then searches for an AFIB entry
that matches the OAL header AFVI or an IP forwarding table entry that
matches the OAL destination address.
Gateways process carrier packets that contain OAL packets/fragments
with OAL destinations that do not match their ULA or the SRT Subnet
Router Anycast address 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 ULA or the
SRT Subnet Router Anycast address as the OAL destination. If the OAL
packet/fragment contains an OCH or a full OAL header with a CRH-32
extension, the Gateway examines the AFVI to locate the AFV entry in
the AFIB for next hop forwarding. If an AFV is found, the Gateway
uses the next hop AFVI to forward the OAL packet/fragment to the next
hop while decrementing the OAL Hop Limit but without reassembling.
If the Gateway has a NCE for the target Client with an entry for the
target underlay interface and current L2 addresses, the Gateway
instead forwards the OAL packet/fragment directly to the target
Client while using the final hop AFVI instead of the next hop (see:
Section 4.13.4).
If the OAL packet/fragment includes a full OAL header addressed to
itself but does not include an AFVI, the Gateway instead reassembles
if necessary, verifies the OAL checksum, and processes the OAL packet
further. The Gateway first determines whether the OAL packet
includes an NS/NA 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 ULA, the Gateway
instead reassembles then discards the OAL header and forwards the
original IP packet/parcel to the network layer to support secured BGP
routing protocol control messaging. The Gateway instead drops all
other OAL packets.
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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 a single IPv6 routing table that always determines the same
next hop for a given OAL destination, where the secured/unsecured
spanning tree is determined through the selection of the underlay
interface to be used for transmission (i.e., a secured tunnel or an
open INET interface).
As for Proxy/Servers, Gateways must verify that the L2 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/parcel 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 neighbor or by the
neighbor itself. The message includes an IP header with the address
of the node that generated the error as the source address and with
the link layer 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", "Time Exceeded" and "Parameter Problem"
[RFC0792][RFC4443]. (OMNI interfaces ignore link layer IPv4
"Fragmentation Needed" and IPv6 "Packet Too Big" messages for carrier
packets that are no larger than the minimum/path MPS as discussed in
Section 4.9, however these messages may provide useful hints of probe
failures during path MPS probing.)
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
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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 L2 and OAL ~ a
~ encapsulation headers ~ c
| | k
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ e
| | t
~original IP packet/parcel hdrs ~
~ (first-fragment only) ~ i
| | n
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | e
~ Portion of the body of ~ r
~ the original IP packet/parcel ~ 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].
* 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 begin including integrity checks and/or institute rate
limits for subsequent carrier packets.
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* 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 4.15.5.
* 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 reconverge and correct
the temporary outage.
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.
When an AERO node receives a carrier packet for which OAL reassembly
is currently congested, it returns an OMNI interface Packet Too Big
(PTB) message as discussed in [I-D.templin-intarea-omni] (note that
the PTB messages could indicate either "hard" or "soft" errors).
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.
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4.12. AERO Mobility Service Coordination
AERO nodes observes the Router Discovery and Prefix Registration
specifications found in Section 15 of [I-D.templin-intarea-omni].
AERO nodes further coordinate their autoconfiguration actions with
the mobility service as discussed in the following sections.
4.12.1. AERO Service Model
Each AERO Proxy/Server on the OMNI link is configured to facilitate
Client prefix delegation/registration requests. Each Proxy/Server is
provisioned with a database of MNP-to-Client ID mappings for all
Clients enrolled in the AERO service, as well as any information
necessary to authenticate each Client. 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 service regardless of
the Proxy/Servers they select.
Clients associate each of their ANET/INET underlay interfaces with a
FHS Proxy/Server. 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 Hub Proxy/Server (the Client may
instead select a "third-party" Hub 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 Hub Proxy/Server and Client without assuming the
Hub role functions themselves.
Each Client associates with a single Hub Proxy/Server at a time,
while all other Proxy/Servers are candidates for providing the Hub
role for other Clients. An FHS Proxy/Server assumes the Hub role
when it receives an RS message with its own ULA or link-scoped All-
Routers multicast as the destination. An FHS Proxy/Server assumes
the proxy role when it receives an RS message with the ULA of another
Proxy/Server as the destination. (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 ULA of
another Proxy/Server to serve as a Hub.)
Hosts and Clients on ENET interfaces associate with an upstream
Client on the ENET the same as a Client would associate with an ANET
Proxy/Server. In particular, the Host/Client sends an RS message via
the ENET which directs the message to the upstream Client. The
upstream Client returns an RA message. In this way, the downstream
nodes see the ENET as an ANET and see the upstream Client as a Proxy/
Server for that ANET.
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AERO Hosts, Clients and Proxy/Servers use IPv6 ND messages to
maintain neighbor cache entries. 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.,
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 Hub Proxy/Servers include prefix delegation and/or
registration parameters in RS/RA messages. The IPv6 ND messages are
exchanged between the Client and Hub Proxy/Server (via any FHS Proxy/
Servers acting as proxys) according to the prefix management schedule
required by the service. If the Client knows its MNP in advance, it
can employ prefix registration by including its XLA-MNP as the source
address of an RS message and with an OMNI option with valid prefix
registration information for the MNP. If the Hub Proxy/Server
accepts the Client's MNP assertion, it injects the MNP into the
routing system and establishes the necessary neighbor cache state.
If the Client does not have a pre-assigned MNP, it can instead employ
prefix delegation by including a TLA as the source address of an RS
message and with an OMNI option with prefix delegation parameters to
request an MNP.
The following sections outlines Host, Client and Proxy/Server
behaviors based on the Router Discovery and Prefix Registration
specifications found in Section 15 of [I-D.templin-intarea-omni].
These sections observe all of the OMNI specifications, and include
additional specifications of the interactions of Client-Proxy/Server
RS/RA exchanges with the AERO mobility service.
4.12.2. AERO Host and Client Behavior
AERO Hosts and Clients discover the addresses of candidate Proxy/
Servers by resolving the Potential Router List (PRL) in a similar
manner as described in [RFC5214]. Discovery methods include static
configuration (e.g., a flat-file map of Proxy/Server addresses and
locations), or through an automated means such as Domain Name System
(DNS) name resolution [RFC1035]. Alternatively, the Host/Client can
discover Proxy/Server addresses through a data link layer login
exchange, or through an RA response to a multicast/anycast RS as
described below. In the absence of other information, the Host/
Client can resolve the DNS Fully-Qualified Domain Name (FQDN)
"linkupnetworks.[domainname]" where "linkupnetworks" is a constant
text string and "[domainname]" is a DNS suffix for the OMNI link
(e.g., "example.com"). The name resolution returns a set of resource
records with Proxy/Server address information.
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The Host/Client then performs RS/RA exchanges over each of its
underlay interfaces to associate with (possibly multiple) FHS Proxy/
Serves and a single Hub Proxy/Server as specified in Section 15 of
[I-D.templin-intarea-omni]. The Host/Client then sends each RS
(either directly via Direct interfaces, via a VPN for VPNed
interfaces, via an access router for ANET interfaces or via INET
encapsulation for INET interfaces) and waits up to RetransTimer
milliseconds for an RA message reply (see Section 4.12.3) while
retrying up to MAX_RTR_SOLICITATIONS if necessary. If the Host/
Client receives no RAs, or if it receives an RA with Router Lifetime
set to 0, the Client SHOULD abandon attempts through the first
candidate Proxy/Server and try another Proxy/Server.
After the Host/Client registers its underlay interfaces, it may wish
to change one or more registrations, e.g., if an interface changes
address or becomes unavailable, if traffic selectors change, etc. To
do so, the Host/Client prepares an RS message to send over any
available underlay interface as above. The RS includes an OMNI
option with prefix registration/delegation information and with an
Interface Attributes sub-option specific to the selected underlay
interface. When the Host/Client receives the Hub Proxy/Server's RA
response, it has assurance that both the Hub and FHS Proxy/Servers
have been updated with the new information.
If the Host/Client wishes to discontinue use of a Hub Proxy/Server it
issues an RS message over any underlay interface with an OMNI Proxy/
Server Departure sub-option that encodes the (old) Hub Proxy/Server's
ULA. When the Hub Proxy/Server processes the message, it releases
the MNP, sets the NCE state for the Host/Client to DEPARTED and
returns an RA reply with Router Lifetime set to 0. After a short
delay (e.g., 2 seconds), the Hub Proxy/Server withdraws the MNP from
the routing system. (Alternatively, when the Host/Client associates
with a new FHS/Hub Proxy/Server it can include an OMNI "Proxy/Server
Departure" sub-option in RS messages with the ULAs of the Old FHS/Hub
Proxy/Servers.)
4.12.3. AERO Proxy/Server Behavior
AERO Proxy/Servers act as both IP routers and IPv6 ND proxys, and
support a prefix delegation/registration service for Clients. Proxy/
Servers arrange to add their ULAs to the PRL maintained in a static
map of Proxy/Server addresses for the link, the DNS resource records
for the FQDN "linkupnetworks.[domainname]", etc. before entering
service. The PRL should be arranged such that Clients can discover
the addresses of Proxy/Servers that are geographically and/or
topologically "close" to their underlay network connections.
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When a FHS/Hub Proxy/Server receives a prospective Client's RS
message, it SHOULD return an immediate RA reply with Router Lifetime
set to 0 if it is currently too busy or otherwise unable to service
the Client; otherwise, it processes the RS as specified in Section 15
of [I-D.templin-intarea-omni]. When the Hub Proxy/Server receives
the RS, it determines the correct MNPs to provide to the Client by
processing the XLA-MNP prefix parameters and/or the DHCPv6 OMNI sub-
option. When the Hub Proxy/Server returns the MNPs, it also creates
an XLA-MNP forwarding table entry for the MNP resulting in a BGP
update (see: Section 4.2.3). The Hub Proxy/Server then returns an RA
to the Client with destination set to the source of the RS (if an FHS
Proxy/Server on the return path proxys the RA, it changes the
destination to the Client's ULA-MNP).
After the initial RS/RA exchange, the Hub Proxy/Server maintains a
ReachableTime timer for each of the Client's underlay interfaces
individually (and for the Client's NCE collectively) set to expire
after ReachableTime seconds. If the Client (or an FHS Proxy/Server)
issues additional RS messages, the Hub Proxy/Server sends an RA
response and resets ReachableTime. If the Hub Proxy/Server receives
an IPv6 ND message with a prefix release indication it sets the
Client's NCE to the DEPARTED state and withdraws the XLA-MNP route
from the routing system after a short delay (e.g., 2 seconds). If
ReachableTime expires before a new RS is received on an individual
underlay interface, the Hub Proxy/Server marks the interface as DOWN.
If ReachableTime expires before any new RS is received on any
individual underlay interface, the Hub Proxy/Server sets the NCE
state to STALE and sets a 10 second timer. If the Hub Proxy/Server
has not received a new RS or uNA message with a prefix release
indication before the 10 second timer expires, it deletes the NCE and
withdraws the XLA-MNP from the routing system.
The Hub Proxy/Server processes any IPv6 ND messages pertaining to the
Client while forwarding to the Client or responding on the Client's
behalf as necessary. The Hub Proxy/Server may also issue unsolicited
RA messages, e.g., with reconfigure parameters to cause the Client to
renegotiate its prefix delegation/registrations, with Router Lifetime
set to 0 if it can no longer service this Client, etc. The Hub
Proxy/Server may also receive carrier packets via the secured
spanning tree that contain initial data sent while route optimization
is in progress. The Hub Proxy/Server reassembles the enclosed OAL
packets/fragments, then re-encapsulates/re-fragments and sends the
carrier packets to the target Client via an FHS Proxy/Server if
necessary. Finally, If the NCE is in the DEPARTED state, the old Hub
Proxy/Server forwards any OAL packets/fragments it receives from the
secured spanning tree and destined to the Client to the new Hub
Proxy/Server, then deletes the entry after DepartTime expires.
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Note: Clients SHOULD arrange to notify former Hub Proxy/Servers of
their departures, but Hub Proxy/Servers are responsible for expiring
neighbor cache entries and withdrawing XLA-MNP routes even if no
departure notification is received (e.g., if the Client leaves the
network unexpectedly). Hub Proxy/Servers SHOULD therefore set Router
Lifetime to ReachableTime seconds in solicited RA messages to
minimize persistent stale cache information in the absence of Client
departure notifications. A short Router Lifetime also ensures that
proactive RS/RA messaging between Clients and FHS Proxy/Servers will
keep any NAT state alive (see above).
Note: All Proxy/Servers on an OMNI link MUST advertise consistent
values in the RA Cur Hop Limit, M and O flags, Reachable Time and
Retrans Timer fields the same as for any link, since unpredictable
behavior could result if different Proxy/Servers on the same link
advertised different values.
4.12.3.1. Additional Proxy/Server Considerations
AERO Clients register with FHS Proxy/Servers for each underlay
interface. Each of the Client's FHS Proxy/Servers must inform a
single Hub Proxy/Server of the Client's underlay interface(s) that it
services. For Clients on Direct and VPNed underlay interfaces, the
FHS Proxy/Server for each interface is directly connected, for
Clients on ANET underlay interfaces the FHS Proxy/Server is located
on the ANET/INET boundary, and for Clients on INET underlay
interfaces the FHS Proxy/Server is located somewhere in the connected
Internetwork. When FHS Proxy/Server "B" processes a Client
registration, it must either assume the Hub role or forward a proxyed
registration to another Proxy/Server "A" acting as the Hub. Proxy/
Servers satisfy these requirements as follows:
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* when FHS Proxy/Server "B" receives a Client RS message, it first
verifies that the OAL Identification is within the window for the
NCE that matches the {ULA,XLA}-MNP in the RS source address for
this Client neighbor and authenticates the message. If no NCE was
found, Proxy/Server "B" instead creates one in the STALE state and
caches the Client-supplied Interface Attributes, Origin Indication
and OMNI Window Synchronization sub-option parameters as well as
the Client's observed L2 addresses (noting that they may differ
from the Origin addresses if there were NATs on the path). Proxy/
Server "B" then examines the RS destination address. If the
destination address is the ULA of a different Proxy/Server "A",
Proxy/Server "B" prepares a separate proxyed version of the RS
message with an OAL header with source set to its own ULA and
destination set to Proxy/Server B's ULA. Proxy/Server "B" also
writes its own information over the Interface Attributes sub-
option supplied by the Client, omits or zeros the Origin
Indication sub-option then forwards the message into the OMNI link
secured spanning tree.
* when Hub Proxy/Server "A" receives the RS, it assume the Hub role,
delegates an MNP for the Client if necessary according to the
Prefen in a Neighbor Control sub-option included by the Client,
and creates/updates a NCE indexed by the Client's XLA-MNP with FHS
Proxy/Server "B"'s Interface Attributes as the link layer address
information for this FHS ifIndex. Hub Proxy/Server "A" then
prepares an RA message with source set to its own ULA, destination
set to the source of the RS message, and with a Neighbor Control
sub-option with Preflen set to the actual MNP length it will
delegate to the Client. Hub Proxy/Server "A" then encapsulates
the RA in an OAL header with source set to its own ULA and
destination set to the ULA of FHS Proxy/Server, then finally
performs fragmentation if necessary and sends the resulting
carrier packets into the secured spanning tree.
* when FHS Proxy/Server "B" reassembles the RA, it locates the
Client NCE based on the RA destination. If the RA message
includes an OMNI "Proxy/Server Departure" sub-option with non zero
old FHS/Hub Proxy/Server ULAs that do not match its own ULA, FHS
Proxy/Server "B" first sends a uNA to the old FHS/Hub Proxy/
Servers named in the sub-option. If the RA message delegates a
new XLA-MNP, Proxy/Server "B" then resets the RA destination to
the corresponding ULA-MNP for this interface. Proxy/Server "B"
then re-encapsulates the message with OAL source set to its own
ULA and OAL destination set to ULA that appeared in the Client's
RS message OAL source, with an appropriate Identification value,
with an authentication signature if necessary, with the Client's
Interface Attributes sub-option echoed and with the cached
observed L2 addresses written into an Origin Indication sub-
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option. Proxy/Server "B" sets the P flag in the RA flags field to
indicate that the message has passed through a proxy [RFC4389],
includes responsive window synchronization parameters, then
fragments the RA if necessary and returns the fragments to the
Client.
* The Client repeats this process over each of its additional
underlay interfaces while treating each additional FHS Proxy/
Server "C", "D", "E", etc. as a proxy to facilitate RS/RA
exchanges between the Hub and the Client. The Client creates/
updates NCEs for each such FHS Proxy/Server as well as the Hub
Proxy/Server in the process.
After the initial RS/RA exchanges each FHS Proxy/Server forwards any
of the Client's carrier packets that contain OAL packets/fragments
with destinations for which there is no matching NCE to a Gateway
using OAL encapsulation with its own ULA as the source and with
destination determined by the Client. The Proxy/Server instead
forwards any OAL packets/fragments destined to a neighbor cache
target directly to the target according to the OAL or link layer
information - the process of establishing neighbor cache entries is
specified in Section 4.13.
While the Client is still associated with FHS Proxy/Servers "B", "C",
"D", etc., each FHS Proxy/Server can send NS, RS and/or uNA messages
to update the neighbor cache entries of other AERO nodes on behalf of
the Client based on changes in Interface Attributes, Traffic
Selectors, etc. This allows for higher-frequency Proxy-initiated RS/
RA messaging over well-connected INET infrastructure supplemented by
lower-frequency Client-initiated RS/RA messaging over constrained
ANET data links.
If the Hub Proxy/Server "A" ceases to send solicited RAs, FHS Proxy/
Servers "B", "C", "D" can send unsolicited RAs over the Client's
underlay interface with destination set to (link-local) All-Nodes
multicast and with Router Lifetime set to zero to inform Clients that
the Hub Proxy/Server has failed. Although FHS Proxy/Servers "B", "C"
and "D" can engage in IPv6 ND exchanges on behalf of the Client, the
Client can also send IPv6 ND messages on its own behalf, e.g., if it
is in a better position to convey state changes. The IPv6 ND
messages sent by the Client include the Client's XLA-MNP as the
source in order to differentiate them from the IPv6 ND messages sent
by a FHS Proxy/Server.
If the Client becomes unreachable over all underlay interfaces it
serves, the Hub Proxy/Server sets the NCE state to DEPARTED and
retains the entry for DepartTime seconds. While the state is
DEPARTED, the Hub Proxy/Server forwards any OAL packets/fragments
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destined to the Client to a Gateway via OAL encapsulation. When
DepartTime expires, the Hub Proxy/Server deletes the NCE, withdraws
the XLA-MNP route and discards any further carrier packets that
contain OAL packets/fragments destined to the former Client.
In some ANETs that employ a Proxy/Server, the Client's MNP can be
injected into the ANET routing system. In that case, the Client can
send original IP packets/parcels without invoking the OAL so that the
ANET routing system transports the original IP packets/parcels to the
Proxy/Server. This can be beneficial, e.g., if the Client connects
to the ANET via low-end data links such as some aviation wireless
links.
If the ANET first-hop access router is on the same underlay link as
the Client and recognizes the AERO/OMNI protocol, the Client can
avoid OAL encapsulation for both its control and data messages. When
the Client connects to the link, it can send an unencapsulated RS
message with source address set to its own XLA-MNP (or to a TLA), and
with destination address set to the ULA of the Client's selected
Proxy/Server or to link-scoped All-Routers multicast. The Client
includes an OMNI option formatted as specified in
[I-D.templin-intarea-omni]. The Client then sends the unencapsulated
RS message, which will be intercepted by the AERO-aware ANET access
router.
The ANET access router then performs OAL encapsulation on the RS
message and forwards it to a Proxy/Server at the ANET/INET boundary.
When the access router and Proxy/Server are one and the same node,
the Proxy/Server would share an underlay link with the Client but its
message exchanges with outside correspondents would need to pass
through a security gateway at the ANET/INET border. The method for
deploying access routers and Proxys (i.e. as a single node or
multiple nodes) is an ANET-local administrative consideration.
Note: When a Proxy/Server alters the IPv6 ND message contents before
forwarding (e.g., such as altering the OMNI option contents), the
original IPv6 ND message checksum and authentication signature values
are invalidated and must be re-calculated.
Note: When a Proxy/Server receives a secured Client NS message, it
performs the same proxying procedures as for described for RS
messages above. The proxying procedures for NS/NA message exchanges
is specified in Section 4.13.
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4.12.3.2. Detecting and Responding to Proxy/Server Failures
In environments where fast recovery from Proxy/Server failure is
required, FHS Proxy/Servers SHOULD use proactive Neighbor
Unreachability Detection (NUD) to track Hub Proxy/Server reachability
in a fashion that parallels Bidirectional Forwarding Detection (BFD)
[RFC5880]. Each FHS Proxy/Server can then quickly detect and react
to failures so that cached information is re-established through
alternate paths. The NS/NA control messaging is carried only over
well-connected ground domain networks (i.e., and not low-end
aeronautical radio links) and can therefore be tuned for rapid
response.
FHS Proxy/Servers perform continuous NS/NA exchanges with the Hub
Proxy/Server, e.g., one exchange per second. The FHS Proxy/Server
sends the NS message via the spanning tree with its own ULA as the
source and the ULA of the Hub Proxy/Server as the destination, and
the Hub Proxy/Server responds with an NA. When the FHS Proxy/Server
is also sending RS messages to a Hub Proxy/Server on behalf of
Clients, the resulting RA responses can be considered as equivalent
hints of forward progress. This means that the FHS Proxy/Server need
not also send a periodic NS if it has already sent an RS within the
same period. If the Hub Proxy/Server fails (i.e., if the FHS Proxy/
Server ceases to receive advertisements), the FHS Proxy/Server can
quickly inform Clients by sending unsolicited RA messages
The FHS Proxy/Server sends unsolicited RA messages with source
address set to the Hub Proxy/Server's address, destination address
set to (link-local) All-Nodes multicast, and Router Lifetime set to
0. The FHS Proxy/Server SHOULD send MAX_FINAL_RTR_ADVERTISEMENTS RA
messages separated by small delays [RFC4861]. Any Clients that had
been using the failed Hub Proxy/Server will receive the RA messages
and select a different Proxy/Server to assume the Hub role (i.e., by
sending an RS with destination set to the ULA of the new Hub).
4.12.3.3. DHCPv6-Based Prefix Registration
When a Client is not pre-provisioned with an MNP, it will need for
the Hub Proxy/Server to select one or more MNPs on its behalf and set
up the correct state in the AERO routing service. (A Client with a
pre-provisioned MNP may also request the Hub Proxy/Server to select
additional MNPs.) The DHCPv6 service [RFC8415] is used to support
this requirement.
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When a Client needs to have the Hub Proxy/Server select MNPs, it
sends an RS message with source address set to a TLA and with an OMNI
option that includes a DHCPv6 message sub-option with DHCPv6 Prefix
Delegation (DHCPv6-PD) parameters. When the Hub Proxy/Server
receives the RS message, it extracts the DHCPv6-PD message from the
OMNI option.
The Hub Proxy/Server then acts as a "Proxy DHCPv6 Client" in a
message exchange with the locally-resident DHCPv6 server, which
delegates MNPs and returns a DHCPv6-PD Reply message. (If the Hub
Proxy/Server wishes to defer creation of MN state until the DHCPv6-PD
Reply is received, it can instead act as a Lightweight DHCPv6 Relay
Agent per [RFC6221] by encapsulating the DHCPv6-PD message in a
Relay-forward/reply exchange with Relay Message and Interface ID
options.)
When the Hub Proxy/Server receives the DHCPv6-PD Reply, it creates an
XLA based on the delegated MNP adds an XLA-MNP route to the routing
system. The Hub Proxy/Server then sends an RA back to the Client
either directly or via an FHS Proxy/Server acting as a proxy. The
Proxy/Server that returns the RA directly to the Client sets the
(newly-created) ULA-MNP as the destination address and with a
DHCPv6-PD Reply message sub-option coded in the OMNI option. When
the Client receives the RA, it creates a default route, assigns the
Subnet Router Anycast address and sets its {ULA,XLA}-MNP based on the
delegated MNP.
Note: Further details of the DHCPv6-PD based MNP registration (as
well as a minimal MNP delegation alternative that avoids including a
DHCPv6 message sub-option in the RS) are found in
[I-D.templin-intarea-omni].
Note: when the Hub Proxy/Server forwards an RA to the Client via a
different node acting as a FHS Proxy/Server, the Hub sets the RA
destination to the same address that appeared in the RS source. The
FHS Proxy/Server then subsequently sets the RA destination to the
ULA-MNP when it forwards the Proxyed version of the RA to the Client
- see [I-D.templin-intarea-omni] for further details.
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 initial original IP packets/
parcels to new neighbors over ANET/INET interfaces and for ongoing
multilink forwarding coordination with existing neighbors. Address
resolution is based on an IPv6 ND NS/NA(AR) messaging exchange
between an Address Resolution Source (ARS) and the target neighbor as
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the Address Resolution Target (ART). Either the ART itself or the
ART's current Hub Proxy/Server serves as the Address Resolution
Responder (ARR).
Address resolution is initiated by the first eligible ARS closest to
the original source as follows:
* For Clients on VPNed and Direct interfaces, the Client's FHS
Proxy/Server is the ARS.
* For Clients on ANET interfaces, either the Client or the FHS
Proxy/Server may be the ARS.
* For Clients on INET interfaces, the Client itself is the ARS.
* For correspondent nodes on INET/ENET interfaces serviced by a
Relay, the Relay is the ARS.
* For Clients that engage the Hub Proxy/Server in "mobility anchor"
mode, the Hub Proxy/Server is the ARS.
* For peers within the same ANET/ENET, 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 continuous unicast multilink forwarding and
route optimization exchanges to maintain optimal forwarding profiles.
The address resolution, multilink forwarding and route optimization
procedures are specified in the following sections.
4.13.1. Multilink Address Resolution
When one or more original IP packets/parcels from a source node
destined to a target node arrives, the ARS checks for a NCE with an
XLA-MNP that matches the target destination. If there is a NCE in
the REACHABLE state, the ARS invokes the OAL and sends the resulting
carrier packets according to the cached state then returns from
processing.
Otherwise, if there is no NCE the ARS creates one in the INCOMPLETE
state. The ARS then prepares an NS message for Address Resolution
(NS(AR)) to send toward an ART while including the original IP
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packet(s)/parcel(s) as trailing data following the NS(AR) in an OAL
super-packet [I-D.templin-intarea-omni]. The resulting NS(AR)
message must be sent securely, and includes:
* the ULA of the ARS as the source address.
* the XLA corresponding to the original IP packet/parcel's
destination as the Target Address, e.g., for 2001:db8:1:2::10:2000
the Target Address is fd00::2001:db8:1:2.
* the Solicited-Node multicast address [RFC4291] formed from the
lower 24 bits of the original IP packet/parcel's destination as
the destination address, e.g., for 2001:db8:1:2::10:2000 the
NS(AR) destination address is ff02:0:0:0:0:1:ff10:2000.
The NS(AR) message also includes an OMNI option with an
authentication sub-option if necessary, includes Interface Attributes
and/or Traffic Selectors for all of the source Client's underlay
interfaces and a Neighbor Control sub-option with a valid Preflen for
its claimed MNP. The ARS then calculates and includes the
authentication signature (if necessary) followed by the checksum,
then submits the NS(AR) message for OAL encapsulation. The ARS sets
the OAL source to its own ULA and sets the OAL destination according
to the Client's RS message 'U' flag (see:
[I-D.templin-intarea-omni]). If the 'U' flag was set, the ARS sets
the OAL destination to the ULA of its Hub Proxy/Server which
maintains a Report List; otherwise, the ARS sets the destination to
the XLA-MNP corresponding to the ART. The ARS then selects an
identification value, inserts a fragment header, calculates the OAL
checksum, performs fragmentation and L2 encapsulation, then sends the
resulting carrier packets into the SRT secured spanning tree without
decrementing the network layer TTL/Hop Limit field.
When the ARS is a Client, it must instead use the ULA of one of its
FHS Proxy/Servers as the OAL destination. The ARS Client then
fragments, performs L2 encapsulation and forwards the carrier packets
to the FHS Proxy/Server. The FHS Proxy/Server then discards the L2
headers, verifies the Identification, reassembles if necessary,
verifies the NS(AR) checksum/authentication signature and confirms
that the Client's claimed Neighbor Control Preflen is valid for its
ULA-MNP source address. The FHS Proxy/Server then changes the OAL
source to its own ULA and changes the OAL destination to the ULA of
the Hub Proxy/Server or XLA-MNP corresponding to the ART as specified
above. The FHS Proxy/Server next selects an appropriate
Identification, calculates the OAL checksum, re-fragments, performs
L2 encapsulation and sends the resulting carrier packets into the
secured spanning tree on behalf of the Client.
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Note: both the source and target Client/Relay and their Hub Proxy/
Servers include current and accurate information for their multilink
Interface Attributes profile. The Hub Proxy/Servers can be trusted
to provide an authoritative ARR response and/or mobility update
message on behalf of the source/target should the need arise. While
the source or target itself has no such trust basis, any attempt to
mount an attack by providing false Interface Attributes information
would only result in black-holing of return traffic, i.e., the
"attack" could only result in denial of service to the source/target
itself. Therefore, the source/target's asserted Interface Attributes
need not be validated by the Hub Proxy/Server.
4.13.1.1. ARS Hub Proxy/Server NS(AR) Processing
If the ARS Client's Hub Proxy/Server maintains a Report List, the
carrier packets containing the NS(AR) will first arrive at the at the
Hub due to the OAL destination address supplied by the ARS (see
above). This source Hub then discards the L2 headers, reassembles
then records the NS Target Address in the Report List for this source
Client. The Hub then leaves the OAL source address unchanged, but
changes the OAL destination address to the XLA corresponding to the
NS Target Address. The Hub then decrements the OAL header Hop Limit,
includes an appropriate Identification, recalculates the OAL
checksum, refragments, performs L2 encapsulation and sends the
resulting carrier packets into the secured spanning tree.
4.13.1.2. Relaying the NS(AR)
When a Gateway receives carrier packets containing the NS(AR), it
discards the L2 headers and determines the next hop by consulting its
standard IPv6 forwarding table for the OAL header XLA destination
address. The Gateway next decrements the OAL header Hop Limit, then
performs L2 encapsulation and sends the carrier packet(s) via the
secured spanning tree the same as for any IPv6 router, where they may
traverse multiple OMNI link segments. The final-hop Gateway will
deliver the carrier packets via the secured spanning tree to the Hub
Proxy/Server (or Relay) that services the ART.
4.13.1.3. NS(AR) Processing at the ARR/ART
When the Hub Proxy/Server of the ART receives the NS(AR) secured
carrier packets with the XLA-MNP of the ART as the OAL destination,
it discards the L2 headers, verifies the Identification, reassembles
if necessary, verifies the OAL checksum then either forwards the
NS(AR) to the ART or processes it locally if it is acting as a Relay
or as the ART's designated ARR. The Hub Proxy/Server processes the
message as follows:
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* if the NS(AR) target matches a Client NCE in the DEPARTED state,
the (old) Hub Proxy/Server resets the OAL destination address to
the ULA of the Client's new Hub Proxy/Server. The old Hub Proxy/
Server then decrements the OAL header Hop Limit, recalculates the
OAL checksum, re-fragments, includes appropriate L2 headers then
forwards the resulting carrier packets over the secured spanning
tree.
* If the NS(AR) target matches a Client NCE in the REACHABLE state,
the Hub Proxy/Server notes whether the NS(AR) arrived from the
secured spanning tree. If the message arrived via the secured
spanning tree the Hub Proxy/Server verifies the NS checksum only;
otherwise, it must also verify the message authentication
signature. If the Hub Proxy/Server maintains a Report List for
the ART, it next records the NS source address in the Report List
for this ART. If the Hub Proxy/Server is the ART's designated
ARR, it prepares to return an NA(AR) as discussed below;
otherwise, the Hub Proxy/Server determines the underlay interface
for the ART and proceeds as follows:
- If the Hub Proxy/Server is also the FHS Proxy/Server on the
underlay interface used to convey the NS(AR) to the ART, it
includes an authentication signature if necessary then
recalculates the NS(AR) checksum. The Hub then changes the OAL
source to its own ULA and OAL destination to the ULA-MNP of the
ART, decrements the OAL Hop Limit, includes a suitable
identification value, recalculates the OAL checksum, re-
fragments if necessary, includes appropriate L2 headers and
sends the resulting carrier packets over the underlay interface
to the ART.
- If the Hub Proxy/Server is not the FHS Proxy/Server on the
underlay interface used to convey the NS(AR) to the ART, it
instead recalculates the NS(AR) checksum, changes the OAL
source to its own ULA and changes the OAL destination to the
ULA of the FHS Proxy/Server for this ART interface. The Hub
Proxy/Server next decrements the OAL Hop Limit, includes a
suitable Identification value, recalculates the OAL checksum,
re-fragments if necessary, includes appropriate L2 headers and
sends the resulting carrier packets over the secured spanning
tree.
- When the FHS Proxy/Server receives the carrier packets, it
discards the L2 headers, reassembles and verifies the OAL and
NS(AR) checksums, then forwards to the ART the same as
described above.
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* If the NS(AR) target matches one of its non-MNP routes, the Hub
Proxy/Server serves as both a Relay and an ARR, since the Relay
forwards original IP packets/parcels toward the (fixed network)
target at the network layer.
If the ARR is a Relay or the ART itself, it first creates or updates
a NCE for the NS(AR) source address while caching all Interface
Attributes and Traffic Selector information. Next, the ARR prepares
a solicited NA(AR) message to return to the ARS with the source
address set to the ART's XLA, the destination address set to the
NS(AR) ULA source address and the Target Address set to the same
value that appeared in the NS(AR) Target 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 and includes a Neighbor Control sub-
option with the Preflen to apply to the ART's MNP. 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 if necessary, calculates the NA message checksum, then
submits the NA(AR) for OAL encapsulation with source set to its own
ULA and destination set to the ULA that appeared in the NS(AR) OAL
source and selects an appropriate Identification. The ARR then
calculates the OAL checksum, fragments, includes appropriate L2
headers and forwards the resulting (L2-encapsulated) carrier packets.
When the ART Proxy/Server receives carrier packets sent by an ART
acting as an ARR on its own behalf, it reassembles if necessary and
verifies the checksum/authentication signature. The Proxy/Server
then verifies that the Neighbor Control Preflen is acceptable,
changes the OAL source address to its own ULA and changes the OAL
destination to the ULA corresponding to the NA(AR) destination. The
Proxy/Server next decrements the OAL Hop Limit, includes an
appropriate Identification, recalculates the NA and OAL checksums and
fragments if necessary. The Proxy/Server finally includes
appropriate L2 headers and sends the carrier packets into the secured
spanning tree.
4.13.1.4. Relaying the NA(AR)
When a Gateway receives NA(AR) carrier packets, it discards the L2
headers 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, re-encapsulates the carrier
packets with new L2 headers and forwards them via the SRT secured
spanning tree where they may traverse multiple OMNI link segments.
The final-hop Gateway will deliver the carrier packets via the
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secured spanning tree to a Proxy/Server for the ARS.
4.13.1.5. Processing the NA(AR) at the ARS
When the ARS receives the NA(AR) message, it first searches for a NCE
that matches the NA(AR) target address. The ARS then processes the
message the same as for standard IPv6 Address Resolution [RFC4861].
In the process, it caches all OMNI option information in the NCE for
the ART (including Interface Attributes, Traffic Selectors, etc.),
and caches the NA(AR) XLA source address as the address of the ART.
When the ARS is a Client, the SRT secured spanning tree will first
deliver the solicited NA(AR) message to the FHS Proxy/Server, which
re-adjusts the OAL header 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; if the Client is on the open
INET the Proxy/Server must instead include an authentication
signature (while adjusting the OMNI option size, if necessary). The
Proxy/Server uses its own ULA as the OAL source and the ULA-MNP of
the Client as the OAL destination when it forwards the NA(AR). The
Proxy/Server then decrements the OAL Hop Limit, includes an
appropriate Identification, recalculates the OAL checksum, re-
fragments, includes appropriate L2 headers and sends the carrier
packets over the underlay interface to the Client.
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 (or their Proxy/
Servers) can assert multilink forwarding paths through underlay
interface pairs serviced by the same source/destination ULAs by
sending unicast NS/NA messages with OMNI AERO Forwarding Parameter
(AFP) sub-options. The unicast NS/NA messages establish multilink
forwarding state in OAL intermediate nodes in the path between the
ARS and ART. Note that either the ARS or ART can independently
initiate multilink forwarding by sending unicast NS messages on
behalf of specific underlay interface pairs. (Underlay interface
directionality (i.e., in/out) must also be factored into the paths
established for multilink forwarding.)
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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 guide the dispersal of
different traffic types over available multilink paths, while other
factors such as link quality, 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.
Nodes that configure OMNI interfaces and engage in multilink
coordination include an additional forwarding table termed the AERO
Forwarding Information Base (AFIB) that supports OAL packet/fragment
forwarding based on OMNI neighbor underlay interface pairs. The AFIB
contains per-interface-pair AERO Forwarding Vectors (AFVs) identified
by locally-unique values known as AFV Indexes (AFVIs). The AFVs
cache uncompressed OAL header information as well as the previous/
next-hop addressing and AFVI information. The AFVs also cache window
synchronization state for the specific underlay interface pair.
Using the window synchronization state, simple Identification-based
data origin authentication is enabled at each OAL source,
intermediate and target node.
OMNI interfaces manage the AFIB in conjunction with their internal
Neighbor Cache. OMNI interface NCEs link to (possibly) multiple
AFVs, with one AVF per underlay interface pair (according to
directionality). When OMNI interface peers need to coordinate, they
locate a NCE for the peer then use the NCE as a nexus that aggregates
potentially many AVFs. In particular, the NCE caches the AFVI to be
used to index the local AFV at the head end of the path.
OAL source, intermediate and target nodes create AFVs/AFVIs when they
process an NS message with an AFP sub-option with Job code '00'
(Initialize; Build B) or a solicited NA message with Job code '01'
(Follow B; Build A) (see: [I-D.templin-intarea-omni]). The OAL
source of the NS (which is also the OAL destination of the solicited
NA) is considered to reside in the "First Hop Segment (FHS)", while
the OAL destination of the NS (which is also the OAL source of the
solicited NA) is considered to reside in the "Last Hop Segment
(LHS)".
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The FHS and LHS roles are determined on a per-interface-pair basis.
After address resolution, either peer is equally capable of
initiating multilink forwarding on behalf of a specific FHS/LHS
underlay interface pair. The peer that sends the initiating NS with
Job code '00' message for a specific pair becomes the FHS peer while
the one that returns the NA response becomes the LHS peer for that
pair only. It is therefore quite possible (and even commonplace)
that both peers may assume the FHS role for some pairs while assuming
the LHS role for other pairs, i.e., even though each peer maintains
only a single NCE.
When an OAL node initiates or forwards an NS with Job code '00', it
creates an AFV, records the NS source and destination ULAs then
generates and assigns a locally-unique "B" AFVI (while also caching
the "B" values for all previous OAL hops on the path from the FHS OAL
source). When the OAL node receives future OAL packets/fragments
that include "B", it can unambiguously locate the correct AFV and
determine directionality without examining addresses. When the AFV
is indexed by its "B" AFVI, it returns the ULAs in (dst,src) order
the opposite of how they appeared in the OAL header of the original
NS to support full header reconstruction for reverse-path forwarding.
(If the NS message included a nested OAL encapsulation, the ULAs of
both OAL headers are returned.)
When an OAL node initiates or forwards a solicited NA with Job code
'01', it uses the "B" AFVI to locate the AFV created by the NS then
generates and assigns a locally-unique "A" AFVI (while also caching
the "A" values for all previous OAL hops on the path from the LHS OAL
source). When the OAL node receives future carrier packets that
include "A", it can unambiguously locate the correct AFV and
determine directionality without examining addresses. When the AFV
is indexed by its "A" AFVI, it returns the ULAs in (src,dst) order
the same as they appeared in the OAL header of the original NS to
support full header reconstruction for forward-path forwarding. (If
the NS message included a nested OAL encapsulation, the ULAs of both
OAL headers are returned.)
OAL nodes generate random non-zero 32-bit values as candidate AFVIs
which must first be tested for local uniqueness. If a candidate AFVI
s already in use, the OAL node repeats the random generation process
until it obtains a unique non-zero value. Since the number of AFVs
in service at each OAL node is likely to be much smaller than 2**32,
the process will generate a unique value after a small number of
tries. Since the uniqueness property is node-local only, an AFVI
locally generated by a first OAL node must not be tested for
uniqueness by other OAL nodes.
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OAL nodes cache AFVs for up to ReachableTime seconds following their
initial creation. If the node processes another NS or NA message
specific to an AFV, it resets ReachableTime to REACHABLE_TIME
seconds, i.e., the same as for NCEs. If ReachableTime expires, the
node deletes the AFV and frees its associated AFVIs so they can be
reused for future AFVs.
The following sections provide the detailed specifications of these
NS/NA exchanges for all nodes along the forward and reverse paths.
4.13.2.1. FHS Client-Proxy/Server NS Forwarding
When an FHS OAL source has an original IP packet/parcel to send
toward an LHS OAL target, it first performs multilink address
resolution resulting in the creation of a NCE for the XLA of the
target then selects a source and target underlay interface pair. The
FHS source uses its cached information for the target interface as
LHS information then prepares an NS message with an AFP sub-option
with Job code '00', includes window synchronization information, then
sets the NS source to the XLA of the FHS Client and the NS target to
the XLA of the LHS Client. The FHS source next creates an AFV then
generates and assigns a locally-unique "B" AFVI to the AFV while also
including it as the first "B" entry in the AFP AFVI List. The FHS
source then includes any FHS/LHS addressing information it knows
locally in the AFP sub-option, i.e., based on information discovered
through address resolution.
If the FHS source is the FHS Proxy/Server, it then examines the LHS
FMT-Forward code. If FMT-Forward is clear the FHS Proxy/Server sets
the NS destination to the ULA of the LHS Proxy/Server; otherwise, it
sets the NS destination to the same address as the target. The FHS
Proxy/Server then performs OAL encapsulation while setting the OAL
source to its own ULA and setting the OAL destination to the FHS
Subnet Router Anycast ULA determined by applying the FHS SRT prefix
length to its ULA. The FHS Proxy/Server then selects an appropriate
Identification value, calculates the OAL checksum, fragments if
necessary, encapsulates in appropriate L2 headers then sends the
carrier packets into the secured spanning tree which will deliver
them to a Gateway interface that assigns the FHS Subnet Router
Anycast ULA.
If the FHS source is the FHS Client, it instead includes an
authentication signature if necessary. If LHS FMT-Forward is clear,
the FHS Client sets the NS destination to the ULA of the LHS Proxy/
Server; otherwise, it sets the NS destination to the same address as
the target. The FHS Client then calculates the NS message checksum,
performs OAL encapsulation, sets the OAL source to its own ULA-MNP
and sets the OAL destination to the ULA of the FHS Proxy/Server. The
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FHS Client finally selects an appropriate Identification value for
the FHS Proxy/Server, calculates the OAL checksum, fragments if
necessary, encapsulates in appropriate L2 headers then sends the
carrier packets to the FHS Proxy/Server.
When the FHS Proxy/Server receives the carrier packets, it discards
the L2 headers then verifies the Identification, reassembles if
necessary, verifies the OAL checksum and verifies the NS checksum/
authentication signature. The FHS Proxy/Server then creates an AFV
(i.e., the same as the FHS Client had done) while caching the AFP "B"
entry along with the FHS Client addressing information as previous
hop information for this AFV. The FHS Proxy/Server next generates a
new locally-unique "B" AFVI, then assigns it as the AFV index and
writes it as the next "B" entry in the AFP AFVI List (while also
writing any FHS Client and Proxy/Server addressing information). The
FHS Proxy/Server then calculates the NS checksum and sets the OAL
source address to its own ULA and destination address to the FHS
Subnet Router Anycast ULA. The FHS Proxy/Server finally decrements
the OAL Hop Limit, includes an Identification appropriate for the
secured spanning tree, calculates the OAL checksum and re-fragments
if necessary. The FHS Proxy/Server finally includes appropriate L2
headers and sends the carrier packets into the secured spanning tree.
4.13.2.2. Gateway NS 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 OAL packet/fragment
over the secured spanning tree addressed to its ULA or the FHS Subnet
Router Anycast ULA, it instead reassembles to obtain the NS then
verifies the OAL and NS checksums. The FHS Gateway next creates an
AFV (i.e., the same as the FHS Proxy/Server had done) while caching
the AFP FHS Client and Proxy/Server addressing information, window
synchronization information and corresponding AFVI List "B" values in
the AFV to enable future reverse path forwarding to this FHS Client.
The FHS Gateway then generates a locally-unique "B" AFVI for the AFV
and writes it as the next "B" entry in the NS AFP AFVI List.
The FHS Gateway then examines the SRT prefixes corresponding to both
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 NS AFP LHS information in
the AFV, writes its LHS ULA and L2ADDR into the NS AFP LHS fields,
then sets its LHS ULA as the OAL source and the ULA of the LHS Proxy/
Server as the OAL destination. If the FHS and LHS prefixes are
different, the FHS Gateway instead sets its FHS ULA as the OAL source
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and the LHS Subnet Router Anycast ULA as the OAL destination. The
FHS Gateway then decrements the OAL Hop Limit, selects an appropriate
Identification, recalculates the NS and OAL checksums, re-fragments
if necessary, then finally includes appropriate L2 headers and sends
the carrier packets 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 simply forward the enclosed OAL
packets/fragments without further processing. The LHS Gateway then
reassembles to obtain the NS, verifies the OAL and NS checksums then
creates an AFV (i.e., the same as the FHS Gateway had done) while
caching the AFP "B" AFVIs and addressing information of previous OAL
forwarding hops along with window synchronization information. In
particular, the LHS Gateway caches the ULA of the FHS Gateway as the
spanning tree address for the previous-hop, caches the LHS
information then generates a locally-unique "B" AFVI for the AFV.
The LHS Gateway then writes its own LHS ULA and L2ADDR into the AFP
sub-option while also writing "B" as the next entry in the AFP AFVI
List. The LHS Gateway then sets its own ULA as the OAL source and
the ULA of the LHS Proxy/Server as the OAL destination, decrements
the OAL Hop Limit, selects an appropriate Identification,
recalculates the NS and OAL checksums, re-fragments if necessary,
then finally includes appropriate L2 headers and sends the carrier
packets into the secured spanning tree.
4.13.2.3. LHS Proxy/Server-Client NS Receipt and NA Forwarding
When the LHS Proxy/Server receives the carrier packets from the
secured spanning tree, it discards the L2 headers, reassembles if
necessary, verifies the OAL and NS checksums then verifies that the
LHS information supplied by the FHS source is consistent with its own
cached information. If the information is consistent, the LHS Proxy/
Server then creates an AFV and caches the AFP "B" AFVIs and
addressing information of previous OAL forwarding hops the same as
for the prior hop. The LHS Proxy/Server next caches the NS window
synchronization parameters in the AFV. If the NS destination is the
XLA of the LHS Client, the LHS Proxy/Server also generates a locally-
unique "B" AFVI and assigns it both to the AFV and as the next "B"
entry in the NS AFVI List.
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If the NS destination matches its own ULA, the LHS Proxy/Server next
prepares to return a solicited NA with Job code '01'. The LHS Proxy/
Server next creates or updates an NCE for the NS source address (if
necessary) with state set to STALE and with an AFVI pointer to the
new AFV state. When the LHS Proxy/Server forwards future carrier
packets based on the cached information, it can populate forwarding
information in a CRH-32 routing header to enable forwarding based on
the cached AFVI List "B" entries.
The LHS Proxy/Server then creates an NA with Job code '01' while
copying the NS AFP sub-option into the NA and including responsive
window synchronization information. The LHS Proxy/Server then
generates a locally-unique "A" AFVI and both assigns it to the AFV
and includes it as the first "A" entry in the AFP sub-option AFVI
List (see: [I-D.templin-intarea-omni] for details on AFVI List A/B
processing). The LHS Proxy/Server then encapsulates the NA with OAL
source set to its own ULA and OAL destination set to the ULA of the
LHS Gateway. The LHS Proxy/Server then selects an appropriate
Identification value, calculates the NA and OAL checksums, fragments
if necessary then finally includes appropriate L2 headers and
forwards the carrier packets into the secured spanning tree.
If the NS destination was the XLA of the LHS Client, the LHS Proxy/
Server includes an authentication signature in the NS if necessary,
then recalculates the NS checksum, changes the OAL source to its own
ULA and changes the OAL destination to the ULA-MNP of the LHS Client.
The LHS Proxy/Server then decrements the OAL Hop Limit, selects an
appropriate Identification value, calculates the OAL checksum,
fragments if necessary then finally includes appropriate L2 headers
and sends the carrier packets to the LHS Client. When the LHS Client
receives the carrier packets, it discards the L2 headers, verifies
the Identification, reassembles if necessary, then verifies the OAL
checksum and NS checksum/authentication signature. The LHS Client
then creates a NCE for the NS ULA source address (if necessary) in
the STALE state and examines the AFP sub-option. The Client then
caches the NS OMNI AFP sub-options in the NCE corresponding to the NS
ULA source, then creates an AFV, caches the addressing information
and "B" entries of the previous OAL hops then finally generates and
assigns a locally-unique "A" AFVI the same as for previous hops. The
Client finally caches the new AFVI in the NCE so that future
communications can locate the correct AFV.
The LHS Client then prepares an NA using exactly the same procedures
as for the LHS Proxy/Server above (while including responsive window
synchronization information), except that it uses its XLA as the NA
source and the NS source as the NA destination. The LHS Client also
includes an authentication signature if necessary, calculates the NA
message checksum, then encapsulates the NA with OAL source set to its
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own ULA-MNP and OAL destination set to the ULA of the LHS Proxy/
Server. The LHS Client finally includes an appropriate
Identification, calculates the OAL checksum, fragments if necessary
then includes appropriate L2 headers and sends the carrier packets to
the LHS Proxy/Server. When the LHS Proxy/Server receives the carrier
packets, it discards the L2 headers verifies the Identifications,
reassembles if necessary, verifies the OAL checksum and NA checksum/
authentication signature, then uses the current AFP AFVI List "B"
entry to locate the AFV. The LHS Proxy/Server then caches the
addressing and "A" information for the LHS Client in the AFV, then
generates a locally-unique "A" AFVI and both assigns it to the AFV
and writes it as the next AFP AFVI List "A" entry. The LHS Proxy/
Server then calculates the NA checksum, sets the OAL source to its
own ULA and destination to the ULA of the LHS Gateway, decrements the
OAL Hop Limit, includes an appropriate Identification, calculates the
OAL checksum, re-fragments if necessary then finally includes
appropriate L2 headers and sends the carrier packets into the secured
spanning tree.
4.13.2.4. Gateway NA Forwarding
When the LHS Gateway receives the carrier packets containing the NA
message, it discards the L2 headers, reassembles if necessary,
verifies the OAL and NA checksums then uses the current NA AFP AFVI
List "B" entry to locate the AFV. The LHS Gateway then caches the
AFP addressing and AFVI List "A" information for the previous hops in
the AFV, then generates a locally-unique "A" AFVI and both assigns it
to the AFV and writes it as the next AFP AFVI List "A" entry. The
LHS Gateway then recalculates the NA checksum. If the LHS Gateway is
connected directly to both the FHS and LHS segments (whether the
segments are the same or different), the LHS Gateway will have
already cached the FHS/LHS information based on the original NS; the
LHS Gateway then sets the OAL source to its FHS ULA and OAL
destination to the ULA of the FHS Proxy/Server. Otherwise, the LHS
Gateway sets the OAL source to its LHS ULA and OAL destination to the
ULA of the FHS Gateway. The LHS Gateway then decrements the OAL Hop
Limit, selects an appropriate Identification, recalculates the OAL
checksum, re-fragments if necessary, includes appropriate L2 headers
and finally sends the carrier packets into the secured spanning tree.
When the FHS and LHS Gateways are different, the FHS Gateway will
receive carrier packets containing the NA message from the LHS
Gateway over the secured spanning tree, where there may have been
many intermediate Gateway forwarding hops. The FHS Gateway then
discards the L2 headers, reassembles if necessary, verifies the OAL
and NA checksums and locates the AFV based on the current AFP AFVI
List "B" entry. The FHS Gateway then caches the addressing and "A"
information for the previous hops in the AFV and generates a locally-
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unique "A" AFVI. The FHS Gateway then assigns the new "A" value to
the AFV, records "A" in the AFP AFVI List then writes its FHS ULA and
L2ADDR into the AFP FHS Gateway fields. The FHS Gateway then
recalculates the NA checksum, sets its FHS ULA as the OAL source and
sets the ULA of the FHS Proxy/Server as the OAL destination. The FHS
Gateway then decrements the OAL Hop Limit, selects an appropriate
Identification value, recalculates the OAL checksum, re-fragments if
necessary, includes appropriate L2 headers and finally sends the
carrier packets into the secured spanning tree.
4.13.2.5. FHS Proxy/Server-Client NA Receipt
When the FHS Proxy/Server receives the carrier packets from the
secured spanning tree, it discards the L2 headers, reassembles if
necessary, verifies the OAL and NA checksums then locates the AFV
based on the current AFP AFVI List "B" entry. The FHS Proxy/Server
then caches the AFP addressing and "A" information for the previous
hops. If the NA destination matches its own ULA, the FHS Proxy/
Server locates the NCE for the ULA of the LHS Proxy/Server or XLA of
the LHS Client and sets the state to REACHABLE. The FHS Proxy/Server
then caches the window synchronization parameters and prepares to
return an acknowledgement, if necessary.
If the NA destination is the XLA of the FHS Client, the FHS Proxy/
Server instead generates a locally-unique "A" AFVI and assigns it
both to the AFV and as the next AFP AFVI List "A" entry, then
includes an authentication signature/checksum in the NA message. The
FHS Proxy/Server then sets the OAL source to its own ULA and sets the
OAL destination to the ULA-MNP of the FHS Client. The FHS Proxy/
Server then decrements the OAL Hop Limit, selects an appropriate
Identification value, recalculates the OAL checksum, re-fragments if
necessary, includes appropriate L2 headers and finally sends the
carrier packets to the FHS Client.
When the FHS Client receives the carrier packets, it discards the L2
headers, verifies the Identification, reassembles if necessary,
verifies the OAL checksum and NA checksum/authentication signature,
then locates the AFV based on the current AFP AFVI List "B" entry.
The FHS Client then caches the previous hop addressing and "A"
information the same as for prior hops. The FHS Client then locates
the NCE for the NS source address and sets the state to REACHABLE,
then caches the window synchronization parameters and prepares to
return a uNA acknowledgement, if necessary.
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4.13.2.6. Returning Window Acknowledgements
If either the FHS Client or FHS Proxy/Server needs to return an
acknowledgement to complete window synchronization, it prepares a uNA
message with an AFP sub-option with Job code set to '10' (Follow A;
Record B). The FHS node sets the uNA source to its own ULA or XLA,
then sets the uNA destination to the ULA or XLA of the LHS node. The
FHS node next sets the AFP AFVI List to the cached list of "A"
entries received in the Job code '01' NA, but need not set any other
FHS/LHS information. The FHS node then encapsulates the uNA message
in an OAL header with its own ULA as the OAL source. If the FHS node
is the Client, it next sets the ULA of the FHS Proxy/Server as the
OAL destination, includes an authentication signature/checksum,
selects an appropriate Identification value, calculates the OAL
checksum, fragments if necessary, includes appropriate L2 headers and
finally sends the carrier packets to the FHS Proxy/Server. The FHS
Proxy/Server then verifies the Identification, reassembles if
necessary, verifies the OAL checksum and uNA checksum/authentication
signature, then uses the current AFVI List "A" entry to locate the
AFV.
The FHS Proxy/Server then writes its "B" AFVI as the next AFP AFVI
List "B" entry, recalculates the uNA checksum then sets its own ULA
as the OAL source and the ULA of the FHS Gateway as the OAL
destination, The FHS Proxy/Server finally decrements the OAL Hop
Limit, selects an appropriate Identification, recalculates the OAL
checksum, includes appropriate L2 headers and finally sends the
carrier packets into the secured spanning tree. When the FHS Gateway
receives the carrier packets, it discards the L2 headers, reassembles
if necessary, verifies the OAL and uNA checksums then uses the
current AFVI List "A" entry to locate the AFV. The FHS Gateway then
writes its "B" AFVI as the next AFP AFVI List "B" entry, then sets
the OAL source to its own ULA. If the FHS Gateway is also the LHS
Gateway, it sets the OAL destination to the ULA of the LHS Proxy/
Server; otherwise it sets the OAL destination to the ULA of the LHS
Gateway. The FHS Gateway recalculates the uNA checksum then
decrements the OAL Hop Limit, selects an appropriate Identification,
recalculates the OAL checksum, re-fragments if necessary, includes
appropriate L2 headers and finally sends the carrier packets into the
secured spanning tree. If an LHS Gateway receives the carrier
packets, it processes them exactly the same as the FHS Gateway had
done while re-setting the OAL destination to the ULA of the LHS
Proxy/Server.
When the LHS Proxy/Server receives the carrier packets, it discards
the L2 headers, verifies the Identification, reassembles if necessary
then verifies the OAL and uNA checksums. The LHS Proxy/Server then
locates the AFV based on the current AFP AFVI List "A" entry. If the
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uNA destination matches its own ULA, the LHS Proxy/Server next
updates the NCE/AFV for the source ULA based on the uNA window
synchronization parameters and MAY compare the AFVI List to the
version it had cached in the AFV based on the original NS.
If the uNA destination is the XLA of the LHS Client, the LHS Proxy/
Server instead writes its "B" AFVI as the next AFP AFVI List "B"
entry and includes an authentication signature/checksum. The LHS
Proxy/Server then writes its own ULA as the OAL source and the ULA-
MNP of the Client as the OAL destination, then decrements the OAL Hop
Limit, selects an appropriate Identification and recalculates the OAL
checksum. The LHS Proxy/Server finally re-fragments if necessary,
includes appropriate L2 headers and sends the resulting carrier
packets to the LHS Client. When the LHS Client receives the carrier
packets, it discards the L2 headers, verifies the Identification,
reassembles if necessary, verifies the OAL checksum and uNA checksum/
authentication signature then processes the message exactly the same
as for the LHS Proxy/Server case above.
Note: If either the LHS Client or LHS Proxy/Server needs to return an
acknowledgement to complete window synchronization, it prepares a uNA
message with an AFP sub-option with Job code set to '11' (Follow B;
Record A). All other procedures are exactly the opposite as per the
FHS case specified above.
4.13.2.7. OAL End System Exchanges Following Synchronization
Following the initial NS/NA exchange with AFP sub-options, OAL end
systems can begin exchanging ordinary carrier packets that include
"A/B" AFVIs and with Identification values within their respective
send/receive windows without requiring security signatures and/or
secured spanning tree traversal. OAL end systems and intermediate
nodes can also consult their AFIBs when they receive carrier packets
that contain OAL packets/fragments with "A/B" AFVIs to unambiguously
locate the correct AFV and can use any discovered "A/B" values of
other OAL nodes to forward OAL packets/fragments to nodes that
configure the corresponding AFVIs. OAL end systems must then perform
continuous NS/NA exchanges to update window state, register new
interface pairs 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-interface-pair basis and tracked in the
AFVs which are also linked to the appropriate NCE. However, the
window synchronization exchange only confirms target Client
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reachability over the specific underlay interface pair. Reachability
for other underlay interfaces that share the same window
synchronization state must be determined individually using
additional NS/NA messages.
To update AFIB state in the path, the FHS node that sent the original
NS message with AFP Job code '00' can send additional NS messages
with AFP sub-options with Job code '10' (Follow "A"; Record "B") and
with window synchronization parameters. The message will be
processed by all intermediate OAL nodes which will refresh AFV
timers, cache window synchronization parameters and forward the NS
onward toward the LHS node that returned the original NA message.
When the LHS node receives the NS, it returns an NA message with AFP
Job code '11' (Follow "B"; Record "A").
At the same time, the LHS node that received the original NS message
with Job code '00' can send additional NS messages with Job code '11'
in order to cause the FHS node to return an NA message with AFP Job
code '10'. The process can therefore be coordinated asynchronously
with the FHS/LHS nodes initiating an NS/NA exchange independently of
one another. The exchanges will succeed as long as the AFIB state in
the path remains active. Note that all intermediate node processing
of Job code '10' and '11' NS/NA messages is conducted the same as for
the initial NS/NA exchange according to the detailed specifications
above.
OAL sources can also begin including CRH-32s in OAL packets/fragments
with AFVI information that OAL intermediate nodes can use for
shortest-path forwarding based on AFVIs instead of spanning tree
addresses. OAL sources and intermediate nodes can instead forward
OAL packets/fragments with OAL compressed headers termed "OCH" (see:
[I-D.templin-intarea-omni]) that include only a single "A/B" AFVI
meaningful to the next hop, since all OAL nodes in the path up to
(and sometimes including) the OAL destination have already
established AFVs. Note that when an FHS OAL source receives a
solicited NA with Job code '01', the AFP sub-option will contain an
AFVI List with "A" entries populated in the reverse order needed for
populating a CRH-32 routing header. The FHS OAL source must
therefore write the AFP AFVI List "A" entries last-to-first when it
populates a CRH-32, or must select the correct "A" entry to include
in an OCH header based on the intended OAL intermediate node or
destination.
When a Gateway receives unsecured carrier packets that contain OAL
packets/fragments destined to a local SRT segment Client that has
asserted direct reachability, the Gateway performs direct forwarding
while bypassing the local Proxy/Server based on the Client's
advertised AFVIs and discovered NATed L2ADDR information (see:
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Section 4.13.4). If the Client cannot be reached directly (or if NAT
traversal has not yet converged), the Gateway instead forwards OAL
packets/fragments directly to the local segment Proxy/Server.
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 IPv6 ND message, the
Proxy/Server uses the Client's NCE established through RS/RA
exchanges to re-encapsulate/re-fragment while sending outbound
secured carrier packets via the secured spanning tree and sending
inbound secured carrier packets while including an 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 NS/NA exchange
between the Client and the remote SRT segment peer, and forwards the
OAL packet/fragments without first reassembling/decapsulating.
When a source Client forwards OAL packets/fragments it can employ
header compression according to the AFVIs established through an NS/
NA exchange with a remote or local peer. When the source Client
forwards to a remote peer, it can forward OAL packets/fragments to a
local SRT Gateway (following the establishment of L2ADDR information)
while bypassing the Proxy/Server following route optimization (see:
Section 4.13.4). 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 if necessary to obtain the OAL packet then
decapsulates and delivers the original IP packet/parcel 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 L2ADDR
addresses, they can exchange carrier packets that contain OAL
packets/fragments directly with header compression using AFVIs
discovered as above (see: Section 4.13.5). The FHS Client will have
cached the "A" AFVI for the LHS Client, which will have cached the
"B" AFVI for the FHS Client.
When the FHS Client or FHS Proxy/Server sends an NS for the purpose
of establishing multilink forwarding state, it should wait up to
RETRANS_TIMER seconds to receive a responsive NA. The FHS node can
then retransmit the NS up to MAX_UNICAST_SOLICIT times before giving
up. Note that each successive attempt establishes new AFV state in
the OAL intermediate nodes, but that any abandoned stale AFV state
will be quickly reclaimed.
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4.13.2.8. Rapid Commit Multilink Forwarding
Multilink forwarding can often be invoked simultaneously with Address
Resolution in order to reduce control message overhead and round-trip
delays. When an ART acting as an ARR receives an NS(AR) with a set
of Interface Attributes for the ARS source Client, it can perform
"rapid commit" by immediately invoking multilink forwarding as above
at the same time as returning the NA(AR).
In order to perform rapid commit, the ARR includes an AFP sub-option
with Job code '00' and a Window Synchronization sub-option as though
it were initiating a multilink coordination NS/NA exchange as
specified above. The ARR then includes any Interface Attributes and/
or Traffic Selector sub-options as necessary to satisfy the address
resolution request, and can also include ordinary original IP
packets/parcels as additional super-packet extensions to this NA(AR)
message if it has immediate data to send to the ARS. The ARR then
returns the NA(AR) to the ARS using the same hop-by-hop OAL
addressing disciplines as specified above for an ordinary multilink
NS/NA exchange. This will cause the NA(AR) to visit all OAL
intermediate nodes on the path towards the ARS.
When the NA(AR) traverses the return path to the ARS, OAL
intermediate nodes in the path process the NS AFP information exactly
the same as for an ordinary multilink forwarding exchange as
specified above, i.e., without examining the remaining NA(AR) message
contents. This results in the ARR node now assuming the FHS role and
the ARS assuming the LHS role from the perspective of multilink
forwarding coordination. When the NA(AR) arrives, the ARS processes
the AFP and window synchronization parameters while also processing
all other NA(AR) OMNI option information, thereby eliminating an
extraneous message transmission and associated delay. The ARS (now
acting as an LHS peer) then completes the exchange by returning a
responsive NA with an AFP sub-option with Job code '01'; if no NA
response is received within RETRANS_TIMER seconds, the ARR can
retransmit the NA(AR) up to MAX_NEIGHBOR_ADVERTISEMENT times before
giving up.
This very importantly implies that the type of IPv6 ND message used
to convey an AFP with Job codes '00' and '01' (i.e., NS or NA) is
unimportant from the perspective of multilink forwarding. This means
that Job code '00' serves as the solicitation indication and Job code
'01' serves as the response such that either an NS or NA message
carrying an AFP with Job code '00' will invoke a responsive NA
message carrying an AFP with Job code '01'.
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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 ANETs
coordinated as Mobile Ad-hoc NETworks (MANETs). 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 addresses they configure locally, including
TLAs and HHITs. 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], OLSR [RFC7181], AODV [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.
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 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. This will cause the network layer to
direct outbound packets to the OMNI interface, which can apply header
compression and underlay MANET interface selection.
When two Clients within the same MANET communicate using IP addresses
that are advertised in the MANET routing protocol, their OMNI
interfaces can avoid OAL encapsulation and treat the IP header
supplied by the network layer as if it were an OAL encapsulation
header. This includes the application of OAL fragmentation and
header compression as discussed in the OMNI specification.
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Proxy/Servers that connect a MANET to the rest of the OMNI link act
as regular Proxy/Servers for exchanges with external INETs, but act
as Clients over their MANET interfaces. Each such Proxy/Server
therefore has at least two underlay interfaces, including an INET
interface and a MANET interface. The Proxy/Server therefore services
the MANET as if it were an ordinary Client but presents itself as a
Proxy/Server to external facing INETs.
The process for a multihop Client to establish header compression
state in the MANET is conducted as a MANET-local aspect of the NS/NA
multilink forwarding message exchange discussed in Section 4.13.2.
The process can be used to establish either asymmetric or symmetric
path header compression state. In the asymmetric case, the forward
path from the source Client to the destination Client or a MANET
border Proxy/Server may be different than the reverse path. In the
symmetric case, both the forward and reverse paths traverse the same
set of MANET routers.
When the OMNI interface of a MANET source Client sends an NS to
establish asymmetric path header compression state, it also includes
a CRH-16 extension header and Window Synchronization parameters. The
source Client selects a non-zero 16-bit "C" AFVI that is unique for
the L2 address of the next MANET forwarding hop for the NS message
and writes that value into the first SID field of the CRH-16 while
writing the value 0 into the second SID field. The source Client
then caches the full OAL header in an AFV for the destination and
sends the NS to the next hop.
When the next MANET forwarding hop's OMNI interface receives the NS,
it creates an AFV and caches the full OAL header as well as the
previous hop's "C" AFVI, L2 address and Window Synchronization
parameters for the forward path. The OMNI interface then selects its
own non-zero/unique "C" AFVI and over-writes that value into the
first SID field of the CRH-16. Consecutive MANET forwarding hops
then repetitively forward the NS to their respective next hops, which
perform the same procedures as above. The process continues until
the NS reaches either a final destination within the same MANET or a
MANET border Proxy/Server that can forward to destinations in other
networks.
When the final destination is within the same MANET, the destination
OMNI interface returns an NA with a CRH-16 and uses the same non-
zero/unique "C" AVFI discipline described above in the reverse path
which may travel over a completely different set of MANET routers
than those in the forward path. Otherwise, the Proxy/Server that
receives the NS forwards it to other networks according to the same
multilink forwarding procedures discussed in Section 4.13.2. When
the Proxy/Server eventually receives an NA to return to the original
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source, the Proxy/Server inserts a CRH-16 (while removing the CRH-32
if present) and performs the same reverse path forwarding that an
ordinary MANET destination would perform as described above. When
the original source receives the NA, header compression state will
have been completely populated in both the forward and reverse paths
and the source and destination nodes can begin sending ordinary
packets with OCH-1/2 headers instead of full OAL headers.
The same procedures that appear above also apply when an NS
originating from a remote network arrives at a MANET border Proxy/
Server for a MANET that contains the final destination. The Proxy/
Server assumes the source role, inserts a CRH-16 with a non-zero/
unique "C" AFVI and forwards it to the next MANET forwarding hop
toward the final destination. The forwarding process continues
between successive MANET routers until the final destination receives
the NS. The final destination then prepares a responsive NA again
while inserting a CRH-16 with a non-zero/unique "C" AFVI and returns
the NA through the MANET toward the same Proxy/Server that forwarded
the NS. Note that it is important that the NA message contains the
OAL address of the same Proxy/Server, since that is the only location
where state resides to enable the return of the NA message to the
original source.
In order to establish symmetric MANET paths, the initiating Client
can instead send an NS that includes a CRH-16 with a non-zero/unique
2-octet "D" AFVI written into the second SID field and 0 written into
the first SID field. The Client then forwards the NS message to the
next MANET forwarding hop toward the destination. When the next
MANET forwarding hop receives the NS, it creates an AFV and caches
the (previous hop) "D" AFVI, then overwrites the second CRH-16 SID
field with a newly-generated (next hop) non-zero/unique "D" AFVI
value. Consecutive MANET forwarding hops then repetitively forward
the NS and create new AFVs in the same fashion until the NS reaches
either a final destination within the same MANET or a MANET border
Proxy/Server.
The destination or Proxy/Server then returns an NA along the reverse
path with the (previous hop) "D" AFVI in the second CRH-16 SID field,
and with a newly-generated (next hop) non-zero/unique "C" AFVI in the
first CRH-16 SID field. When the previous MANET hop processes the
NA, it locates the AFV based on the "D" AFVI, caches the "C" AFVI and
generates a new non-zero/unique "C" AFVI. The MANET node then
overwrites the second CRH-16 SID with its cached previous hop "D"
value and overwrites the first CRH-16 SID with the new "C" AFVI value
and returns the NA to the previous hop. The process continues until
the NA message reaches the original multihop Client that transmitted
the NS, at which point header compression state is established in
both the forward and reverse directions of the MANET symmetric path.
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Following the NS/NA exchanges in both the asymmetric and symmetric
cases discussed above, each MANET router in the path in both the FHS
and LHS MANETs will have established AFVs containing header
compression state. The AFVs determine AFVI-based forwarding based on
the OCH-1/2 header contents, and each MANET router only forwards
packet with in-window Identification values. MANET routers maintain
AFVs for up to ReachableTime seconds unless they are refreshed by
either a new NS/NA exchange or the transmission of any data packet
with a full OAL header with an in-window Identification value and a
CRH-16 extension. 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. Client/Gateway Route Optimization
Following multilink route optimization for specific underlay
interface pairs, FHS/LHS Clients located on open INETs can invoke
Client/Gateway route optimization to improve performance and reduce
load and congestion on their respective Proxy/Servers. To initiate
Client/Gateway route optimization, the Client prepares an NS message
with its own XLA address as the source and the ULA of its Gateway as
the destination while creating a NCE for the Gateway if necessary.
The NS message must be no larger than the minimum MPS and
encapsulated as an atomic fragment.
The Client then includes an Interface Attributes sub-option for its
underlay interface as well as an authentication signature but does
not include window synchronization parameters. The Client then
performs OAL encapsulation with its own ULA-MNP as the source and the
ULA of the Gateway as the destination while including a randomly-
chosen Identification value, then performs L2 encapsulation on the
atomic fragment and sends the resulting carrier packet directly to
the Gateway.
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When the Gateway receives the carrier packet, it removes the L2
headers, verifies the NS checksum/authentication signature then
creates a NCE for the Client. The Gateway then caches the L2
encapsulation addresses (which may have been altered by one or more
NATs on the path) as well as the Interface Attributes for this Client
ifIndex, and marks this Client underlay interface as "trusted". The
Gateway then prepares an NA reply with its own ULA as the source and
the XLA of the Client as the destination where the NA again must be
no larger than the minimum MPS.
The Gateway then echoes the Client's Interface Attributes, includes
an Origin Indication with the Client's observed L2 addresses and
includes an authentication signature. The Gateway then performs OAL
encapsulation with its own ULA as the source and the ULA-MNP of the
Client as the destination while using the same Identification value
that appeared in the NS, then performs L2 encapsulation on the atomic
fragment and sends the resulting carrier packet directly to the
Client.
When the Client receives the NA reply, it caches the carrier packet
L2 source address information as the Gateway target address via this
underlay interface while marking the interface as "trusted". The
Client also caches the Origin Indication L2 address information as
its own (external) source address for this underlay interface.
After the Client and Gateway have established NCEs as well as
"trusted" status for a particular underlay interface pair, each node
can begin sending ordinary carrier packets intended for this
multilink route optimization directly to one another while omitting
the Proxy/Server from the forwarding path while the status is
"trusted". The NS/NA messaging will have established the correct
state in any NATs in the path so that NAT traversal is naturally
supported. The Client and Gateway must maintain a timer that watches
for activity on the path; if no carrier packets and/or NS/NA messages
are sent or received over the path before NAT state is likely to have
expired, the underlay interface pair status becomes "untrusted".
Thereafter, when the Client sends a carrier packet that contains an
OAL packet/fragment toward the Gateway as the next hop, the Client
includes the AFVI for the Gateway (discovered during multilink route
optimization) instead of the AFVI for its Proxy/Server; the Gateway
will accept the OAL packet/fragment from the Client if and only if
the AFVI matches the correct AFV and the underlay interface status is
trusted. (The same is true in the reverse direction when the Gateway
sends carrier packets directly to the Client.)
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Note that the Client and Gateway each maintain a single NCE, but that
the NCE may aggregate multiple underlay interface pairs. Each
underlay interface pair may use differing source and target L2
addresses according to NAT mappings, and the "trusted/untrusted"
status of each pair must be tested independently. When no "trusted"
pairs remain, the NCE is deleted.
Note that the above method requires Gateways to participate in NS/NA
message authentication signature application and verification. In an
alternate approach, the Client could instead exchange NS/NA messages
with authentication signatures via its Proxy/Server but addressed to
the ULA of the Gateway, and the Proxy/Server and Gateway could relay
the messages over the secured spanning tree. However, this would
still require the Client to send additional messages toward the L2
address of the Gateway to populate NAT state; hence the savings in
complexity for Gateways would result in increased message overhead
for Clients.
4.13.5. Client/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 the shared segment
Gateway) 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 the initial
NS/NA exchange 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 for one or both when FMT-Forward and FMT-
Mode are both 1). The NS/NA messages then include an Origin
Indication (i.e., in addition to an AFP sub-option) with the mapped
addresses 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 L2 address for the target Client
which primes its local chain of NATs for reception of future carrier
packets from that L2 address (see: [RFC4380] and
[I-D.templin-intarea-omni]). The source Client then prepares an NS
message with its own XLA as the source, with the XLA of the target as
the destination and with an OMNI option with an Interface Attributes
sub-option. The source Client then encapsulates the NS in an OAL
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header with its own ULA-MNP as the source, with the ULA-MNP of the
target Client as the destination and with an in-window Identification
for the target. The source Client then fragments the NS and
encapsulates the resulting fragments in L2 headers addressed to its
Proxy/Server then sends the resulting carrier packets to the Proxy/
Server.
When the Proxy/Server receives the carrier packets, it re-
encapsulates and sends them as unsecured carrier packets according to
AFIB state where they will eventually arrive at the target Client
which can verify that the identifications are within the acceptable
window and reassemble if necessary. Following reassembly, the target
Client prepares an NA message with its own XLA as the source, with
the XLA of the source Client as the destination and with an OMNI
option with an Interface Attributes sub-option. The target Client
then encapsulates the NA in an OAL header with its own ULA-MNP as the
source, with the ULA-MNP of the source Client as the destination and
with an in-window Identification for the source Client. The target
Client then fragments and encapsulates in L2 headers addressed to the
source Client's Origin addresses then forwards the resulting carrier
packets directly to the source Client.
Following the initial NS/NA exchange, 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-1/2/3 encapsulated carrier
packets. While the Clients continue to exchange packets via the
direct path avoiding all Proxy/Servers and Gateways, they should
perform additional NS/NA exchanges via their local Proxy/Servers to
refresh NCE state as well as send additional bubbles to the peer's
Origin address information if necessary to refresh NAT state.
Note that these procedures are suitable 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 also that each communicating pair of Clients may need to
maintain NAT state for peer to peer communications via multiple
underlay interface pairs. It is therefore important that Origin
Indications are maintained with the correct peer interface and that
the NCE may cache information for multiple peer interfaces.
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Note that the source and target Client exchange Origin information
during the secured NS/NA multilink route optimization exchange. This
allows for subsequent NS/NA 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.
4.13.6. Intra-ANET/ENET Route Optimization for AERO Peers
When a Client forwards an OAL packet (or original IP packet/parcel)
from a Host or another Client connected to one of its downstream
ENETs to a peer within the same downstream ENET, the Client returns
an IPv6 ND Redirect message to inform the source that that target can
be reached directly. The contents of the Redirect message are the
same as specified in [RFC4861], and should also include a Neighbor
Control sub-option with the Preflen of the MNP found in the Target
Address field.
In the same fashion, when a Proxy/Server forwards an OAL packet (or
original IP packet/parcel) from a Host or Client connected to one of
its downstream ANETs to a peer within the same downstream ANET, the
Proxy/Server returns an IPv6 ND Redirect message.
All other route optimization functions are conducted per the NS/NA
messaging discussed in the previous sections.
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 example, IPv6 ND message exchanges that include
authentication codes and/or in-window Identifications may be
considered as acceptable hints of forward progress, while spurious
random carrier packets should be ignored.
AERO nodes can perform NS/NA exchanges over the OMNI link secured
spanning tree (i.e. the same as described above) to test reachability
without risk of DoS attacks from nodes pretending to be a neighbor.
These NS/NA messages use the unicast XLAs/ULAs of the parties
involved in the NUD test. When only reachability information is
required without updating any other NCE state, AERO nodes can instead
perform NS/NA exchanges directly between neighbors without employing
the secured spanning tree as long as they include in-window
Identifications and an authentication signature/checksum.
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After route optimization directs a source FHS peer to a target LHS
peer with one or more link layer addresses, either node may invoke
multilink forwarding state initialization to establish authentic
intermediate node state between specific underlay interface pairs
which also tests their reachability. Thereafter, either node acting
as the source may perform additional reachability probing through NS
messages over the SRT secured or unsecured spanning tree, or through
NS messages sent directly to an underlay interface of the target
itself. While testing a target underlay interface, the source can
optionally continue to forward OAL packets/fragments via alternate
interfaces, maintain a small queue of carrier packets until target
reachability is confirmed or include them as trailing data with the
NS in an OAL super-packet [I-D.templin-intarea-omni].
NS messages are encapsulated, fragmented and transmitted as carrier
packets the same as for ordinary original IP data packets/parcels,
however the encapsulated destinations are either the ULA or XLA of
the source and either the ULA of the LHS Proxy/Server or the XLA of
the target itself. The source encapsulates the NS message the same
as described in Section 4.13.2 and includes an Interface Attributes
sub-option with ifIndex set to identify its underlay interface used
for forwarding. The source then includes an in-window
Identification, fragments the OAL packet, includes L2 encapsulations
and sends the resulting carrier packets into the unsecured spanning
tree, either directly to the target if it is in the local segment or
directly to a Gateway in the local segment.
When the target receives the NS carrier packets, it discards the L2
headers, verifies that it has a NCE for this source and that the
Identification is in-window then reassembles if necessary. The
target next verifies the NS checksum/authentication signature, then
searches for Interface Attributes in its NCE for the source that
match the NS for the NA reply. The target then prepares the NA with
the source and destination addresses reversed, encapsulates and sets
the OAL source and destination, includes an Interface Attributes sub-
option in the NA to identify the ifIndex of the underlay interface
the NS arrived on and sets the Target Address to the same value
included in the NS. The target next sets the R flag to 1, the S flag
to 1 and the O flag to 1, then selects an in-window Identification
for the source and performs fragmentation. The node then performs L2
encapsulation and sends the carrier packets into the unsecured
spanning tree either directly to the source if it is in the local
segment or directly to a Gateway in the local segment.
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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 small 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 Hub Proxy/Servers
via RS/RA exchanges to maintain the DMM profile, and the AERO routing
system tracks all current Client/Proxy/Server peering relationships.
Hub Proxy/Servers provide a designated router service for their
dependent Clients, while FHS Proxy/Servers provide a proxy conduit
between the Client and both the Hub and OMNI link in general.
Clients are responsible for maintaining neighbor relationships with
their Proxy/Servers through periodic RS/RA exchanges, which also
serves to confirm neighbor reachability. When a Client's underlay
interface attributes change, the Client is responsible for updating
the Hub 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 NS/NA
exchange to re-seed new AFVs in the path.
Mobility management considerations are specified in the following
sections.
4.15.1. Mobility Update Messaging
Mobile Clients (and/or their Hub Proxy/Servers) accommodate mobility
and/or multilink change events by sending secured uNA messages to
each active neighbor. When a node sends a uNA message to each
specific neighbor on behalf of a mobile Client, it sets the IPv6
source address to its own ULA or XLA, sets the destination address to
the neighbor's ULA or XLA and sets the Target Address to the mobile
Client's XLA. The uNA also includes an OMNI option with OMNI
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Interface Attributes and Traffic Selector sub-options for the mobile
Client's underlay interfaces and includes an authentication signature
if necessary. The node then sets the uNA R flag to 1, S flag to 0
and O flag to 1, then encapsulates the message in an OAL header with
source set to its own ULA and destination set to either the specific
neighbor's ULA or the FHS Proxy/Server's ULA. 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 probability, 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 set the SNR flag in the uNA
OMNI option header to request a uNA response (see: Section 4.5.1).
When the FHS/LHS Proxy/Server receives a secured uNA message prepared
as above, if the uNA destination was its own ULA the Proxy/Server
uses the included OMNI option information to update its NCE for the
target but does not reset ReachableTime since the receipt of a uNA
message does not provide confirmation that any forward paths to the
target Client are working. If the destination was the XLA of the
FHS/LHS Client, the Proxy/Server instead changes the OAL source to
its own ULA, includes an authentication signature if necessary, and
includes an in-window Identification for this Client. Finally, if
the uNA message SNR flag was set, the node that processes the uNA
also returns a uNA response (see: Section 4.5.1).
4.15.2. Announcing 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), the Client sends RS messages to its Hub Proxy/
Server (via first-hop 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 first FHS Proxy/Server may change due to the underlay
interface change. 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 4.15.5);
otherwise, any stale state in the former FHS Proxy/Server will simply
expire after ReachableTime expires with no effect on the Hub Proxy/
Server.
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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.
After performing the RS/RA exchange, the Client sends uNA messages to
all neighbors the same as described in the previous section.
4.15.3. Bringing New Links Into Service
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 Hub 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 appropriate link quality values
and with link layer address information for the new link. The Client
then again sends uNA messages to all neighbors the same as described
above.
4.15.4. Deactivating Existing Links
When a Client needs to deactivate an existing underlay interface, it
sends a uNA message toward the Hub Proxy/Server via an FHS Proxy/
Server with an OMNI option with appropriate Interface Attributes
values for the deactivated link - in particular, the link quality
value 0 assures that neighbors will cease to use the link.
If the Client needs to send uNA messages over an underlay interface
other than the one being deactivated, it MUST include Interface
Attributes with appropriate link quality values for any underlay
interfaces being deactivated. The Client 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 neighbor cache entries. 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.
4.15.5. Moving Between Proxy/Servers
The Client performs the procedures specified in Section 4.12.2 when
it first associates with a new Hub Proxy/Server or renews its
association with an existing Hub Proxy/Server.
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When a Client associates with a new Hub Proxy/Server, it sends RS
messages to register its underlay interfaces with the new Hub while
including the old Hub's ULA in the "Old Hub Proxy/Server ULA" field
of a Proxy/Server Departure OMNI sub-option. When the new Hub Proxy/
Server returns the RA message via the FHS Proxy/Server (acting as a
proxy), the FHS Proxy/Server sends a uNA to the old Hub Proxy/Server
(i.e., if the ULA is non-zero and different from its own). The uNA
has the XLA of the Client as the source and the ULA of the old hub as
the destination and with an OMNI Proxy/Server Departure sub-option as
above. The FHS Proxy/Server encapsulates the uNA in an OAL header
with the ULA of the new Hub as the source and the ULA of the old Hub
as the destination, the fragments, performs L2 encapsulation and
sends the resulting carrier packets via the secured spanning tree.
When the old Hub Proxy/Server receives the carrier packets, it
decapsulates and reassembles if necessary to obtain the uNA then
changes the Client's NCE state to DEPARTED, resets DepartTime and
caches the new Hub Proxy/Server ULA. After a short delay (e.g., 2
seconds) the old Hub Proxy/Server withdraws the Client's MNP from the
routing system. While in the DEPARTED state, the old Hub Proxy/
Server forwards any carrier packets received via the secured spanning
tree destined to the Client's ULA-MNP to the new Hub Proxy/Server's
ULA. When DepartTime expires, the old Hub 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 Departure sub-option with a ULA for the "Old FHS Proxy/
Server ULA", and the new FHS Proxy/Server will issue a uNA using the
same procedures as outlined for the Hub above while using its own ULA
as the source address. This can often result in successful delivery
of carrier packets that would otherwise be lost due to the mobility
event.
Clients SHOULD NOT move rapidly between Hub 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 Hub
Proxy/Server include a Hub 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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4.16. Multicast
Each Client provides an IGMP (IPv4) [RFC2236] or MLD (IPv6) [RFC3810]
proxy service for its ENETs 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, VPNed
or Direct interfaces, and Relays also act as OMNI link PIM routers on
behalf of nodes on other links/networks.
Clients on VPNed, Direct or ANET underlay interfaces for which the
ANET has deployed native multicast services forward IGMP/MLD messages
into the ANET. The IGMP/MLD messages may be further forwarded by a
first-hop ANET access router acting as an IGMP/MLD-snooping switch
[RFC4541], then ultimately delivered to an ANET (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 ANET/INET underlay
interfaces without native multicast services instead send 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].
For each S belonging to a prefix reachable via X's OMNI interface, X
sends an NS(AR) message (see: Section 4.13) using its own ULA or XLA
as the source address, the solicited node multicast address
corresponding to S as the destination and the XLA of S as the target
address. X then encapsulates the NS(AR) in an OAL header with source
address set to its own ULA and destination address set to the ULA for
S, then forwards the message 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 for any
underlay interfaces that are currently servicing S.
When X processes the NA(AR) it selects one or more underlay
interfaces for S and performs an NS/NA multilink forwarding exchange
over the secured spanning tree while including a PIM Join/Prune
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message for each multicast group of interest in the OMNI option. If
S is located behind any Proxys "Z"*, each Z* then updates its MRIB
accordingly and maintains the XLA 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 NS/NA 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 NS/NA 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 a uNA message to X the same as specified for unicast
mobility in Section 4.15. When X receives the uNA message, it
updates its NCE for the XLA for source S and sends new Join messages
in NS/NA 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 NS message with its own ULA or XLA as the source address
and the ULA or XLA for R as the destination address, then
encapsulates the NS message in an OAL header with its own ULA as the
source and the ULA of R's Proxy/Server as the destination then 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/parcels in PIM Register messages, includes the
PIM Register messages in the OMNI options of uNA messages, performs
OAL encapsulation and fragmentation with Identification values within
the receive window for Client R* that aggregates R, then performs L2
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encapsulation and sends the resulting carrier packets. Client R* may
then elect to send a PIM Join to S* in the OMNI option of a uNA 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/parcel; one native copy from the (S,
G) tree and a second copy from the pre-existing (*, G) tree that
still uses uNA PIM Register encapsulation. R can then issue a uNA
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/
parcels via uNA 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/parcels 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.
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).
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The Client's network layer can select the outgoing 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/parcels 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/parcel over multiple hops to
the target.
4.18. DNS Considerations
AERO Client MNs and INET correspondent nodes consult the Domain Name
System (DNS) the same as for any Internetworking node. When
correspondent nodes and Client MNs use different IP protocol versions
(e.g., IPv4 correspondents and IPv6 MNs), the INET DNS must maintain
A records for IPv4 address mappings to MNs which must then be
populated in Relay NAT64 mapping caches. In that way, an IPv4
correspondent node can send original IPv4 packets/parcels to the IPv4
address mapping of the target MN, and the Relay will translate the
IPv4 header and destination address into an IPv6 header and IPv6
destination address of the MN.
When an AERO Client registers with an AERO Proxy/Server, the Proxy/
Server can return the address(es) of DNS servers in RDNSS options
[RFC6106]. The DNS server provides the IP addresses of other MNs and
correspondent nodes in AAAA records for IPv6 or A records for IPv4.
4.19. 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
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distributing its MNPs and/or discovering non-MNP IP GUA prefixes 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. Or, if an INET partition is transitioned to a
native IP protocol version and addressing scheme that is compatible
with the OMNI link MNP-based addressing scheme, the partition and
OMNI link can be joined by Gateways.
Relays that connect INETs/ENETs with dissimilar IP protocol versions
may need to employ a network address and protocol translation
function such as NAT64 [RFC6146].
4.20. Proxy/Server-Gateway Bidirectional Forwarding Detection
In environments where rapid failure recovery is required, 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 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.
4.21. 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-intarea-omni]) to be used as the Client ID seed
for MNP prefix delegation. The Client would then be obligated to
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renumber its internal networks whenever its MNP (and therefore also
its XLA) changes. This should not present a challenge for Clients
with automated network renumbering services, however presents limits
for the durations of ongoing sessions that would prefer to use a
constant address.
5. Implementation Status
An early AERO implementation based on OpenVPN (https://openvpn.net/)
was announced on the v6ops mailing list on January 10, 2018 and an
initial public release of the AERO proof-of-concept source code was
announced on the intarea mailing list on August 21, 2015.
Many AERO/OMNI functions are implemented and undergoing final
integration. OAL fragmentation/reassembly buffer management code has
been cleared for public release.
6. IANA Considerations
The IANA has assigned the UDP port number "8060" for an experimental
first edition of AERO [RFC6706]. This document together with OMNI
[I-D.templin-intarea-omni] reclaims UDP port number "8060" as the
service port for AERO/OMNI UDP/IP encapsulation. This document makes
no IANA request, since the OMNI specification already provides IANA
guidance. (Note: although [RFC6706] was not widely implemented or
deployed, it need not be obsoleted since its messages use the invalid
ICMPv6 message type number '0' which implementations of this
specification can easily distinguish and ignore.)
No further IANA actions are required.
7. Security Considerations
AERO Gateways configure underlay interface secured tunnels with AERO
Proxy/Servers and Relays within their local OMNI link segments.
Applicable secured tunnel alternatives include IPsec [RFC4301], TLS/
SSL [RFC8446], DTLS [RFC6347], WireGuard [WGD], etc. The AERO
Gateways of all OMNI link segments in turn configure underlay
interface secured tunnels with neighboring AERO Gateways for other
OMNI link segments in a secured spanning tree topology. Therefore,
control messages exchanged between any pair of OMNI link neighbors
over the secured spanning tree are already protected. (Note that
this inter-segment Gateway arrangement mirrors the "half-gateway"
model discussed in the original Catenet proposal.)
To prevent unauthorized local applications from congesting the
secured spanning tree, Proxy/Servers and Gateways should configure
local firewall settings to permit only the BGP protocol service
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daemon to source routing protocol control messages with the ULA
assigned to the OMNI interface as the source and the ULA of a
neighboring Proxy/Server or Gateway as the destination. This could
be implemented as 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 ULA 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 NS/NA
messages they process for the same (source, target) pair, e.g., by
applying IPv6 ND MAX_UNICAST_SOLICIT; MAX_NEIGHBOR_ADVERTISEMENT
limits. This is especially true for NS/NA messages that include
ordinary original IP data packets/parcels as part of a super-packet.
To prevent spoofing vectors, Proxy/Servers MUST discard without
responding to any unsecured IPv6 ND messages that include OMNI sub-
options that would affect state. Also, Proxy/Servers MUST discard
without forwarding any original IP packets/parcels 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 discard without sending any carrier packets that
include an OAL packet/fragment with source and destination that both
match the same MNP.
AERO Clients that connect to secured ANETs need not apply security to
their IPv6 ND messages, since the messages will be authenticated and
forwarded by a perimeter Proxy/Server that applies security on its
INET-facing interface as part of the secured spanning tree (see
above). AERO Clients connected to the open INET can use network and/
or transport layer security services such as VPNs or can by some
other means establish a direct link to a Proxy/Server. When a VPN or
direct link may be impractical, however, INET Clients and Proxy/
Servers SHOULD include and verify authentication signatures for IPv6
ND messages as specified in [I-D.templin-intarea-omni].
Application endpoints SHOULD enable transport or higher layer
security services such as QUIC-TLS, TLS/SSL, DTLS, etc. to assure the
same level of protection as for critical secured Internet services.
AERO Clients 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 can also provide a network-based VPN
service on behalf of the Client, e.g., if the Client is located
within a secured enclave and cannot establish a VPN on its own
behalf.
For INET partitions that require strong security in the data plane,
two options for securing communications include 1) disable route
optimization so that all traffic is conveyed over the secured
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spanning tree, or 2) enable on-demand secure tunnel creation between
Client neighbors. Option 1) would result in longer routes than
necessary and impose traffic concentration on critical infrastructure
elements. Option 2) could be coordinated between Clients using NS/NA
messages with OMNI Host Identity Protocol (HIP) "Initiator/Responder"
message sub-options [RFC7401][I-D.templin-intarea-omni] or QUIC-TLS
protocol message sub-options [RFC9000][RFC9001][RFC9002] to establish
a secured session on-demand.
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
ENETs 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 PRL MUST be well-managed and secured from unauthorized tampering,
even though the list contains only public information. 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.).
The AERO service for 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 all open INET Proxy/
Servers. Similarly, each Client must be able to determine the public
key of each Proxy/Server, e.g. by consulting an online database.
When AERO nodes register their public keys indexed by a unique Host
Identity Tag (HIT) [RFC7401] in a distributed database such as the
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DNS, and use the HIT as an identity for applying IPv6 ND message
authentication signatures, a means for determining public key
attestation is available.
Security considerations for IPv6 fragmentation and reassembly are
discussed in [I-D.templin-intarea-omni]. 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.
SRH authentication facilities are specified in [RFC8754]. 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, Mark
Andrews, Fred Baker, 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,
Wayne Benson, Madhuri Madhava Badgandi, Vijayasarathy Rajagopalan,
Bhargava Raman Sai Prakash, Katie Tran and Eric Yeh are especially
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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]
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.
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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.
9. References
9.1. Normative References
[I-D.templin-intarea-omni]
Templin, F., "Transmission of IP Packets over Overlay
Multilink Network (OMNI) Interfaces", Work in Progress,
Internet-Draft, draft-templin-intarea-omni-28, 3 April
2023, <https://datatracker.ietf.org/doc/html/draft-
templin-intarea-omni-28>.
[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>.
[RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in
IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473,
December 1998, <https://www.rfc-editor.org/info/rfc2473>.
[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>.
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[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>.
[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.
[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.
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[I-D.bonica-6man-comp-rtg-hdr]
Bonica, R., Kamite, Y., Alston, A., Henriques, D., and L.
Jalil, "The IPv6 Compact Routing Header (CRH)", Work in
Progress, Internet-Draft, draft-bonica-6man-comp-rtg-hdr-
29, 14 November 2022,
<https://datatracker.ietf.org/doc/html/draft-bonica-6man-
comp-rtg-hdr-29>.
[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-13, 26 March 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-intarea-
tunnels-13>.
[I-D.ietf-ipwave-vehicular-networking]
Jeong, J. P., "IPv6 Wireless Access in Vehicular
Environments (IPWAVE): Problem Statement and Use Cases",
Work in Progress, Internet-Draft, draft-ietf-ipwave-
vehicular-networking-30, 24 October 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-ipwave-
vehicular-networking-30>.
[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-19, 6
November 2022, <https://datatracker.ietf.org/doc/html/
draft-ietf-rtgwg-atn-bgp-19>.
[I-D.perkins-manet-aodvv2]
Perkins, C. E., Ratliff, S., 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-aodvv2-03, 28 February 2019,
<https://datatracker.ietf.org/doc/html/draft-perkins-
manet-aodvv2-03>.
[I-D.templin-intarea-parcels]
Templin, F., "IP Parcels and Advanced Jumbos", Work in
Progress, Internet-Draft, draft-templin-intarea-parcels-
62, 6 April 2023, <https://datatracker.ietf.org/doc/html/
draft-templin-intarea-parcels-62>.
[IEN48] Cerf, V., "The Catenet Model For Internetworking,
https://www.rfc-editor.org/ien/ien48.txt", July 1978.
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[IEN48-2] Cerf, V., "The Catenet Model For Internetworking (with
figures), http://www.postel.org/ien/pdf/ien048.pdf", July
1978.
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <https://www.rfc-editor.org/info/rfc1035>.
[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>.
[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>.
[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>.
[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>.
[RFC4251] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)
Protocol Architecture", RFC 4251, DOI 10.17487/RFC4251,
January 2006, <https://www.rfc-editor.org/info/rfc4251>.
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[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>.
[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>.
[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>.
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[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>.
[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>.
[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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[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>.
[RFC6221] Miles, D., Ed., Ooghe, S., Dec, W., Krishnan, S., and A.
Kavanagh, "Lightweight DHCPv6 Relay Agent", RFC 6221,
DOI 10.17487/RFC6221, May 2011,
<https://www.rfc-editor.org/info/rfc6221>.
[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>.
[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>.
[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>.
[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>.
[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>.
[RFC7401] Moskowitz, R., Ed., Heer, T., Jokela, P., and T.
Henderson, "Host Identity Protocol Version 2 (HIPv2)",
RFC 7401, DOI 10.17487/RFC7401, April 2015,
<https://www.rfc-editor.org/info/rfc7401>.
[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>.
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[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>.
[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>.
[RFC9001] Thomson, M., Ed. and S. Turner, Ed., "Using TLS to Secure
QUIC", RFC 9001, DOI 10.17487/RFC9001, May 2021,
<https://www.rfc-editor.org/info/rfc9001>.
[RFC9002] Iyengar, J., Ed. and I. Swett, Ed., "QUIC Loss Detection
and Congestion Control", RFC 9002, DOI 10.17487/RFC9002,
May 2021, <https://www.rfc-editor.org/info/rfc9002>.
[WGD] "WireGuard, https://www.wireguard.com", August 2020.
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
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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 L2 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
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/parcels without any encapsulation. In that case, the
Client sends packets/parcels over the Direct link according to
traffic selectors. If the Direct interface is selected, then the
Client's packets/parcels are transmitted directly to the peer without
traversing an ANET/INET. If other interfaces are selected, then the
Client's packets/parcels are transmitted via a different interface,
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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.
AERO Relays are simply Proxy/Servers connected to INETs and/or ENETs
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.
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A.5. AERO Server Failure Implications
AERO Proxy/Servers may appear as a single point of failure in the
architecture, but such is not the case 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 is 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 neighbor cache entries 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 neighbor cache entries 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
neighbor cache entries 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 continuous communications will resume.
Therefore, providing many Proxy/Servers on the link with high
availability profiles provides resilience against loss of individual
Proxy/Servers and assurance that Clients can establish new Proxy/
Server relationships quickly in event of a Proxy/Server failure.
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.
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:
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* 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
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.
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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 >>
Changes from earlier versions:
* Submit for review.
Author's Address
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Fred L. Templin (editor)
Boeing Research & Technology
P.O. Box 3707
Seattle, WA 98124
United States of America
Email: fltemplin@acm.org
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