Automatic Extended Route Optimization (AERO)
draft-templin-6man-aero-47
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".
|
|
|---|---|---|---|
| Author | Fred Templin | ||
| Last updated | 2022-06-10 | ||
| Replaces | draft-templin-intarea-6706bis | ||
| Replaced by | draft-templin-intarea-aero | ||
| RFC stream | Independent Submission | ||
| Formats | |||
| Stream | ISE state | In ISE Review | |
| Consensus boilerplate | Unknown | ||
| Document shepherd | Eliot Lear | ||
| IESG | IESG state | I-D Exists | |
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | rfc-ise@rfc-editor.org |
draft-templin-6man-aero-47
Network Working Group F. L. Templin, Ed.
Internet-Draft Boeing Research & Technology
Intended status: Informational 10 June 2022
Expires: 12 December 2022
Automatic Extended Route Optimization (AERO)
draft-templin-6man-aero-47
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 operation, mobility management, multicast,
traffic path selection 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 12 December 2022.
Copyright Notice
Copyright (c) 2022 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
extracted from this document must include Revised BSD License text as
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Automatic Extended Route Optimization (AERO) . . . . . . . . 16
3.1. AERO Node Types . . . . . . . . . . . . . . . . . . . . . 16
3.2. The AERO Service over OMNI Links . . . . . . . . . . . . 17
3.2.1. AERO/OMNI Reference Model . . . . . . . . . . . . . . 17
3.2.2. Addressing and Node Identification . . . . . . . . . 21
3.2.3. AERO Routing System . . . . . . . . . . . . . . . . . 22
3.2.4. Segment Routing Topologies (SRTs) . . . . . . . . . . 24
3.2.5. Segment Routing For OMNI Link Selection . . . . . . . 25
3.3. OMNI Interface Characteristics . . . . . . . . . . . . . 25
3.4. OMNI Interface Initialization . . . . . . . . . . . . . . 28
3.4.1. AERO Proxy/Server and Relay Behavior . . . . . . . . 28
3.4.2. AERO Client Behavior . . . . . . . . . . . . . . . . 29
3.4.3. AERO Host Behavior . . . . . . . . . . . . . . . . . 29
3.4.4. AERO Gateway Behavior . . . . . . . . . . . . . . . . 30
3.5. OMNI Interface Neighbor Cache Maintenance . . . . . . . . 30
3.5.1. OMNI ND Messages . . . . . . . . . . . . . . . . . . 32
3.5.2. OMNI Neighbor Advertisement Message Flags . . . . . . 34
3.5.3. OMNI Neighbor Window Synchronization . . . . . . . . 34
3.6. OMNI Interface Encapsulation and Fragmentation . . . . . 35
3.7. OMNI Interface Decapsulation . . . . . . . . . . . . . . 37
3.8. OMNI Interface Data Origin Authentication . . . . . . . . 38
3.9. OMNI Interface MTU . . . . . . . . . . . . . . . . . . . 38
3.10. OMNI Interface Forwarding Algorithm . . . . . . . . . . . 39
3.10.1. Host Forwarding Algorithm . . . . . . . . . . . . . 40
3.10.2. Client Forwarding Algorithm . . . . . . . . . . . . 41
3.10.3. Proxy/Server and Relay Forwarding Algorithm . . . . 42
3.10.4. Gateway Forwarding Algorithm . . . . . . . . . . . . 45
3.11. OMNI Interface Error Handling . . . . . . . . . . . . . . 46
3.12. AERO Mobility Service Coordination . . . . . . . . . . . 49
3.12.1. AERO Service Model . . . . . . . . . . . . . . . . . 49
3.12.2. AERO Host and Client Behavior . . . . . . . . . . . 50
3.12.3. AERO Proxy/Server Behavior . . . . . . . . . . . . . 51
3.13. AERO Address Resolution, Multilink Forwarding and Route
Optimization . . . . . . . . . . . . . . . . . . . . . . 58
3.13.1. Multilink Address Resolution . . . . . . . . . . . . 59
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3.13.2. Multilink Forwarding . . . . . . . . . . . . . . . . 64
3.13.3. Rapid Commit Route Optimization . . . . . . . . . . 76
3.13.4. Client/Gateway Route Optimization . . . . . . . . . 77
3.13.5. Client/Client Route Optimization . . . . . . . . . . 79
3.13.6. Client-to-Client OMNI Link Extension . . . . . . . . 80
3.13.7. Intra-ANET/ENET Route Optimization for AERO Peers . 81
3.14. Neighbor Unreachability Detection (NUD) . . . . . . . . . 81
3.15. Mobility Management and Quality of Service (QoS) . . . . 83
3.15.1. Mobility Update Messaging . . . . . . . . . . . . . 84
3.15.2. Announcing Link-Layer Information Changes . . . . . 85
3.15.3. Bringing New Links Into Service . . . . . . . . . . 85
3.15.4. Deactivating Existing Links . . . . . . . . . . . . 85
3.15.5. Moving Between Proxy/Servers . . . . . . . . . . . . 86
3.16. Multicast . . . . . . . . . . . . . . . . . . . . . . . . 87
3.16.1. Source-Specific Multicast (SSM) . . . . . . . . . . 87
3.16.2. Any-Source Multicast (ASM) . . . . . . . . . . . . . 88
3.16.3. Bi-Directional PIM (BIDIR-PIM) . . . . . . . . . . . 89
3.17. Operation over Multiple OMNI Links . . . . . . . . . . . 89
3.18. DNS Considerations . . . . . . . . . . . . . . . . . . . 90
3.19. Transition/Coexistence Considerations . . . . . . . . . . 90
3.20. Proxy/Server-Gateway Bidirectional Forwarding
Detection . . . . . . . . . . . . . . . . . . . . . . . 91
3.21. Time-Varying MNPs . . . . . . . . . . . . . . . . . . . . 91
4. Implementation Status . . . . . . . . . . . . . . . . . . . . 92
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 92
6. Security Considerations . . . . . . . . . . . . . . . . . . . 92
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 95
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 96
8.1. Normative References . . . . . . . . . . . . . . . . . . 96
8.2. Informative References . . . . . . . . . . . . . . . . . 98
Appendix A. Non-Normative Considerations . . . . . . . . . . . . 106
A.1. Implementation Strategies for Route Optimization . . . . 106
A.2. Implicit Mobility Management . . . . . . . . . . . . . . 106
A.3. Direct Underlying Interfaces . . . . . . . . . . . . . . 107
A.4. AERO Critical Infrastructure Considerations . . . . . . . 107
A.5. AERO Server Failure Implications . . . . . . . . . . . . 108
A.6. AERO Client / Server Architecture . . . . . . . . . . . . 109
Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 111
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 111
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-6man-omni]
Non-Broadcast, Multiple Access (NBMA) virtual link model. The OMNI
link is a virtual overlay configured over a network-of-networks
concatenation of underlay Internetworks, and nodes on the link can
exchange original IP packets as single-hop neighbors. 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 provides 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
may 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 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.
AERO Gateways peer with Proxy/Servers in a secured private BGP
overlay routing instance to establish a Segment Routing Topology
(SRT) 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 the 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.
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AERO can be used with OMNI links that span private-use Internetworks
and/or public Internetworks such as the global Internet. In both
cases, Clients may be located behind Network Address Translators
(NATs) on the path to their associated Proxy/Servers. 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 that can connect an Internet of Things (IoT). 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
can also be used to facilitate terrestrial vehicular and urban air
mobility (as well as pedestrian communication services) for future
intelligent transportation systems
[I-D.ietf-ipwave-vehicular-networking][I-D.templin-ipwave-uam-its].
Other applicable use cases are also in scope.
Along with OMNI, AERO provides secured optimal routing support for
the "6M's" of modern Internetworking, including:
1. Multilink - a mobile node's ability to coordinate multiple
diverse underlay data links as a single logical unit (i.e., the
OMNI interface) to achieve the required communications
performance and reliability objectives.
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.
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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. MTU assurance - the ability to deliver packets of various robust
sizes between peers without loss due to a link size restriction,
and to dynamically adjust packets sizes to achieve the optimal
performance 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
terminology in the OMNI specification [I-D.templin-6man-omni] is used
extensively throughout. The following terms are defined within the
scope of this document:
IPv6 Neighbor Discovery (IPv6 ND)
a control message service for coordinating neighbor relationships
between nodes connected to a common link. AERO uses the IPv6 ND
messaging service specified in [RFC4861] in conjunction with the
OMNI extensions specified in [I-D.templin-6man-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.
L2
The Data Link layer in the OSI network model. Also known as
"layer-2", "link-layer", "sub-IP layer", etc.
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L3
The Network layer in the OSI network model. Also known as "layer-
3", "IP layer", etc.
Adaptation layer
A 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 upper layer as "L3" and sees all
lower 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 upper layers. The global
public Internet itself is an example.
End-user Network (ENET)
a simple or complex "downstream" network that travels with the
Client as a single logical unit. 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 Hosts. The ENET
could also provide an "upstream" link in a recursively-descending
chain of additional Clients and ENETs. In this way, an ENET of an
upstream Client is seen as the ANET of a downstream Client.
{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
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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.
OMNI link
the same as defined in [I-D.templin-6man-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 to visit selected waypoints within
the same OMNI link.
OMNI Adaptation Layer (OAL)
an OMNI interface sublayer service that encapsulates original IP
packets admitted into the interface in an IPv6 header and/or
subjects them to fragmentation and reassembly. The OAL is also
responsible for generating MTU-related control messages as
necessary, and for providing addressing context for spanning
multiple segments of an extended OMNI link.
OMNI Interface
a node's attachment to an OMNI link (i.e., the same as defined in
[I-D.templin-6man-omni]). 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.)
L2 encapsulation
the OAL encapsulation of a packet in an outer header or headers
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.
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L2 address(es)
the addresses that appear in the OAL L2 encapsulations for an
underlay interface.
INADDR
the UDP/IP addresses that appear in an L2 address.
original IP packet
a whole IP packet 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 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.
(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 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 carrier packets 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 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.
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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 carrier packets in new L2 headers and
forwards them to the next hop. OAL intermediate nodes decrement
the Hop Limit of the OAL IPv6 header during re-encapsulation, and
discard the packet if the Hop Limit reaches 0. OAL intermediate
nodes do not decrement the Hop Limit/TTL of the original IP
packet.
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-6man-omni]). OMNI links that connect to the global
Internet advertise their MSPs to their interdomain routing peers.
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-6man-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-6man-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-6man-omni]. Clients
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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-6man-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-6man-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.
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. (As
an implementation matter, the Host may instead configure the "OMNI
interface" as a virtual sublayer of the underlay interface
itself.) When an AERO host forwards an original IP packet to
another AERO node on the same ENET, it uses simple IP-in-IP
encapsulation without including an OAL encapsulation header. The
Host is therefore an OMNI link termination endpoint.
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 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
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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.
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 carrier
packets 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
carrier packets received over the secured spanning tree that are
addressed to themselves, while forwarding all other carrier
packets to the next hop also via the secured spanning tree.
Gateways forward carrier packets 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.
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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.
First-Hop Segment (FHS) Proxy/Server
a Proxy/Server for an FHS Client's underlay interface that
forwards the Client's 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 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 that connects
an Internet of Things.
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Mobile Router (MR)
a MN's on-board router that forwards original IP packets between
any downstream-attached networks and the OMNI link. The MR is the
MN entity that hosts the AERO Client.
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.
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.
Multilink Forwarding Information Base (MFIB)
A forwarding table on each OAL source, destination and
intermediate node that includes Multilink Forwarding Vectors (MFV)
with both forwarding instructions and context for reconstructing
compressed headers for specific communicating peer underlay
interface pairs. The MFIB 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.
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Multilink Forwarding Vector (MFV)
An MFIB entry that includes soft state for each underlay interface
pairwise communication session between peer OAL nodes. MFVs are
identified by both a forward and reverse path MFV Index (MFVI).
OAL nodes establish reverse path MFVIs when they forward an IPv6
ND unicast Neighbor Solicitation (NS) message and establish
forward path MFVIs when they forward the solicited IPv6 ND unicast
Neighbor Advertisement (NA) response.
Multilink Forwarding Vector Index (MVFI)
A locally-unique 4 octet value automatically generated by an OAL
node when it creates an MFV. OAL intermediate nodes assign two
distinct MFVIs (called "A" and "B") to each MFV, with "A"
representing the forward path and "B" representing the reverse
path. Meanwhile, the OAL source assigns a single "B" MFVI, and
the OAL destination assigns a single "A" MFVI. Each OAL node
advertises its "A" MFVI to previous hop nodes on the reverse path
toward the source and advertises its "B" MFVI to next hop nodes on
the forward path toward the destination.
Multilink Forwarding Parameters (MFP)
A sub-option of the OMNI option (see: [I-D.templin-6man-omni])
that appears in IPv6 ND NS/NA messages and includes all parameters
necessary for establishing MFV state in OAL nodes in the path.
Throughout the document, the simple terms "Host", "Client", "Proxy/
Server", "Gateway" and "Relay" refer to "AERO Host", "AERO Client",
"AERO Proxy/Server", "AERO Gateway" and "AERO Relay", respectively.
Capitalization is used to distinguish these terms from other common
Internetworking uses in which they appear without capitalization.
The terminology of IPv6 ND [RFC4861], DHCPv6 [RFC8415] and OMNI
[I-D.templin-6man-omni] (including the names of node variables,
messages and protocol constants) is used throughout this document.
The terms "All-Routers multicast", "All-Nodes multicast", "Solicited-
Node multicast" and "Subnet-Router anycast" are defined in [RFC4291].
Also, the term "IP" is used to generically refer to either Internet
Protocol version, i.e., IPv4 [RFC0791] or IPv6 [RFC8200].
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.
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3. Automatic Extended Route Optimization (AERO)
The following sections specify the operation of IP over OMNI links
using the AERO service:
3.1. 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
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 carrier 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)
[I-D.templin-6man-omni]. The OMNI interface and OAL provide a
virtual bridging service, 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 3.2.3). 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.
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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 a
dynamic routing protocol instance to advertise its list of associated
MNPs (see Section 3.2.3). 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 forwarding service for ANET Clients and Hosts to
communicate with peers in external INETs, while Proxy/Servers in the
open INET provide an authentication service for INET Client IPv6 ND
messages but only a secondary forwarding service when the Client
cannot forward directly to a 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 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.
3.2. The AERO Service over OMNI Links
3.2.1. 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 different
administrative authorities and have 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) [I-D.templin-6man-omni] to provide the network layer with
a virtual abstraction similar to a bridged campus LAN. The OAL is an
OMNI interface sublayer that inserts a mid-layer IPv6 encapsulation
header for inter-segment forwarding (i.e., bridging) without
decrementing the network-layer TTL/Hop Limit of the original IP
packet. An example OMNI link SRT is shown in Figure 2:
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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. 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.
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The AERO Multinet service concatenates SRT segments to form larger
networks through Gateway-to-Gateway peerings as originally described
in the "Catenet Model for Internetworking" [IEN48]; especially
Figure 2 follows directly from the illustrations in [IEN48-2]. The
original Catenet vision proposed a "network-of-networks"
concatenation of independent and diverse Internetwork "segments" to
form a much larger network supporting end-to-end services.
The original Catenet vision first articulated in the 1970's was
distorted through the evolution of the Internet in later decades,
since a critical element was missing from the architecture. As a
result, the Internet evolved as a single, large public routing and
addressing domain interconnecting private domains (i.e., instead of a
true network-of-networks) which has impeded flexibility and inhibited
end-to-end services. With the advent of the adaptation layer
established by the AERO/OMNI services, however, the original Catenet
"network-of-networks" vision is now made possible.
3.2.2. 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 in a latent
state and do not employ LLAs for any operational purposes (instead,
nodes assign LLAs solely 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-6man-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-6man-omni] to support OAL addressing. (The prefix
{ULA*}::/64 appearing alone and with no suffix represents "default"
for that prefix.)
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AERO Clients also use Temporary Local Addresses (TLAs) and eXtended
Local Addresses (XLAs) constructed per [I-D.templin-6man-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.
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-6man-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-6man-omni].
3.2.3. 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 carrier packet 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 carrier packets destined to
non-existent more-specific routes are dropped with a Destination
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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 carrier packets 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
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-6man-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::/60, {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.
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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-6man-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
A full discussion of the BGP-based routing system used by AERO is
found in [I-D.ietf-rtgwg-atn-bgp].
3.2.4. 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-6man-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 between
Proxy/Servers and Gateways, while the unsecured spanning tree
forwards 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.
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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.
3.2.5. Segment Routing For OMNI Link Selection
Original IPv6 sources can direct IPv6 packets 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 will traverse when there may be multiple
alternatives.
When an AERO node processes the SRH and forwards the original IPv6
packet 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).
3.3. 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 the open INET 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 any
INET correspondent. 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.
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* 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 be as simple as a
small stub network that travels with a mobile Client (e.g., an
Internet-of-Things) to as complex as a large private enterprise
network that the Client connects to a larger ANET or INET.
* 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 crossing any networked paths. 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 3.6. OMNI interfaces use L2 encapsulation (see:
Section 3.6) 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) 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-6man-omni]. The OMNI option includes
prefix registration information, Interface Attributes and/or
Multilink Forwarding Parameters (MFPs) containing link information
parameters for the OMNI interface's underlay interfaces and any other
per-neighbor information.
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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
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 MFP sub-options with the same underlay interface index.
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 Interface Attributes and/or MFP sub-options with different
underlay interface indexes.
Proxy/Servers on the open Internet include only a single INET
underlay interface. INET Clients therefore discover only the INADDR
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 INADDR information for the Proxy/Server.
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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 and fragment original IP packets
while presenting 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 are run directly over
the OMNI interface and use ULA-RND source and destination addresses.
The OMNI interface employs the OAL to encapsulate the original IP
packets for these sessions as carrier packets (i.e., even though the
OAL header may use the same ULAs as the original IP header) and
forwards them over the secured underlay path.
3.4. 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 with destination
addresses covered by an MNP not explicitly associated with another
interface are directed to an OMNI interface.
OMNI interface initialization procedures for Proxy/Servers, Clients
Hosts and Gateways are discussed in the following sections.
3.4.1. 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 tunnels and engages in BGP routing protocol
sessions with one or more neighboring Gateways.
The OMNI interface provides a single interface abstraction to the IP
layer, but internally includes an NBMA nexus for sending carrier
packets to OMNI interface neighbors over underlay INET interfaces and
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 3.2.3). 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 attachment point of
the OMNI link to a non-MNP-based global topology.
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3.4.2. 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 until it encounters an infrastructure element
that can delegate MNPs.)
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.
3.4.3. 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.
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3.4.4. AERO Gateway Behavior
AERO Gateways configure an OMNI interface and assign a ULA-RND and
corresponding Subnet Router Anycast address for each OMNI link SRT
segment they connect to. Gateways configure 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 3.2.3).
3.5. OMNI Interface Neighbor Cache Maintenance
Each Client, Proxy/Server and Gateway OMNI interface maintains a
conceptual neighbor cache that includes a Neighbor Cache Entry (NCE)
for each of its active neighbors on the OMNI link per [RFC4861].
Each NCE is indexed by the network layer address of the neighbor and
determines the context for Identification verification. Clients and
Proxy/Servers maintain NCEs through RS/RA exchanges, and also
maintain NCEs for any active correspondent peers through NS/NA
exchanges.
Hosts also maintain NCEs for Clients and other Hosts through the
exchange of RS/RA or NS/NA messages. Each NCE is indexed by the
address assigned to the Host ENET interface, which is the same
address used for OMNI 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 also maintain NCEs for Clients within their local segments
based on NS/NA route optimization messaging (see: Section 3.13.4).
When a Gateway creates/updates a NCE for a local segment Client based
on NS/NA route optimization, it also maintains MFVI and INADDR state
for messages destined to this local segment Client.
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 carrier packets destined to the target Client to the
Client's new FHS/Hub Proxy/Server instead. 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 DepartTime
decrements to 0, the NCE is deleted.
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Clients determine the service profiles for their FHS and Hub Proxy/
Servers by setting the N/A/U flags in a Neighbor Coordination sub-
option of the first OMNI option in RS messages. When the N/A/U 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.
To minimize NS/NA message overhead, Clients can set the N/A/U flags
in the OMNI Neighbor Coordination sub-option of RS messages they
send. If the N flag is set, the FHS Proxy/Server that forwards the
RS message assumes the role of responding to NS(NUD) messages and
maintains peer NCEs associated with the NCE for this Client. If the
A 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 U flag is set, the Hub Proxy/Server that
processes the RS message becomes responsible for maintaining a
"Report List" of sources from which it has received an NS(AR) for
this Client NCE. The Hub Proxy/Server maintains each Report List
entry for REPORT_TIME seconds, and sends uNA messages to each member
of the Report List when it receives a Client mobility update
indication (e.g., through receipt of an RS with updated Interface
Attributes, Traffic Selectors, etc.).
Clients and their Hub Proxy/Servers have full knowledge of the
Client's current underlay Interface Attributes, 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 N/A/U flags in the
RS messages they send as discussed above.
Address Resolution Target (ART) Clients and Relays act as Address
Resolution Responders (ARR)s on their own behalf when they receive an
NS(AR) from an Address Resolution Source (ARS) via their Hub Proxy/
Server. The ARR returns an NA(AR) response to the ARS, which creates
or updates a NCE for the target network-layer and link-layer
addresses. The ARS then (re)sets ReachableTime for the NCE to
REACHABLE_TIME seconds and performs reachability tests over specific
underlay interface pairs to determine paths for forwarding carrier
packets directly to the ART. The ARS otherwise decrements
ReachableTime while no further solicited NA messages arrive. It is
RECOMMENDED that REACHABLE_TIME be set to the default constant value
30 seconds as specified in [RFC4861].
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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 unsolicited NAs 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. Most importantly,
DEPART_TIME and REPORT_TIME SHOULD be set to a value that is
sufficiently longer than REACHABLE_TIME to avoid packet loss due to
stale route optimization state.
3.5.1. 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-6man-omni]. OMNI interfaces do not use LLAs as IPv6 ND
message source and destination addresses, but instead use ULAs. This
allows for 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, OMNI interfaces include one or more OMNI
options (and any other ND message options) then completely populate
all option information. If the OMNI interface includes an
authentication signature, it sets the IPv6 ND message Checksum field
to 0 and calculates the authentication signature over the entire
length of the OAL packet or super-packet (beginning with a pseudo-
header of the IPv6 header) but does not then proceed to calculate the
IPv6 ND message checksum itself. Otherwise, the OMNI interface
calculates the standard IPv6 ND message checksum over the OAL packet
or super-packet and writes the value in the Checksum field. OMNI
interfaces verify authentication and integrity of each IPv6 ND
message received according to the specific check(s) included, and
process the message further only following 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
the neighbor cache and provides the basis for the forwarding
algorithm specified in Section 3.10. The information is cumulative
and reflects the union of the OMNI information from the most recent
IPv6 ND messages received from the neighbor; it is therefore not
required that each IPv6 ND message contain all neighbor information.
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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 an OMNI option and S/TLLAO appear, the former
pertains to encapsulation addresses 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
advertisement message includes a Timestamp option, the recipient
should check the Timestamp to determine if the message is current.
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:
* 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/NA(AR) messages must be secured.
* NS/NA(NUD) messages are used determine target reachability and
optionally to also establish MFIB state. The source sends an
NS(NUD) to the unicast address of the target while optionally
including an OMNI Multilink Forwarding Parameters (MFP) sub-option
naming a specific underlay interface pair, and the target returns
a unicast NA(NUD) that echoes the MFP (if present). NS/NA(NUD)
messages that use an in-window sequence number and do not update
any other state need not include an authentication signature but
instead must include an IPv6 ND message checksum. NS/NA(NUD) used
to establish window synchronization and/or MFIB state must be
secured.
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* 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 that update state information must be secured.
* NS/NA(DAD) messages are not used in AERO, since Duplicate Address
Detection is not required.
Additionally, nodes may set the OMNI option PNG flag in NA/RA
messages to receive a uNA response from the neighbor. The uNA
response MUST set the ACK flag (without also setting the SYN or PNG
flags) with the Acknowledgement field set to the Identification used
in the PNG message.
3.5.2. 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/OMNI node types. Simple hosts that would set R to 0 do
not occur on the OMNI link itself, but may occur on the downstream
links of Clients and Relays.
* 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.
3.5.3. 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 Neighbor Coordination
sub-options in NS/NA message exchanges to maintain send/receive
window state in their respective neighbor cache entries as specified
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in [I-D.templin-6man-omni].
3.6. OMNI Interface Encapsulation and Fragmentation
When the network layer forwards an original IP packet 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-6man-omni] which encapsulates the packet in an IPv6
header to produce an OAL packet. For example, an original IP packet
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
checksum and fragments the OAL packet while including an identical
Identification value for each fragment that must be within the window
for the LHS Proxy/Server or the target Client itself. The OAL source
finally includes 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 one or more Multilink Forwarding Vector
Indices (MFVIs) if necessary as discussed in Section 3.13. 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 an OAL 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 Trailing Checksum |
| (final-fragment only) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Carrier Packet Format
Note: the 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 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-6man-omni]. The
OAL source transmits 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 dynamically 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
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maintain a forwarding plane spanning tree that connects all nodes on
the link. The spanning tree supports a carrier packet 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 a Multilink Forwarding
Information Base (MFIB) with Multilink Forwarding Vectors (MFVs) that
can often provide 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 MFIB to greatly
improve performance and reduce load on critical infrastructure
elements.
For carrier packets undergoing re-encapsulation at an OAL
intermediate node, the OMNI interface decrements the OAL IPv6 header
Hop Limit and discards the carrier packet if the Hop Limit reaches 0.
The intermediate node next removes the L2 encapsulation headers from
the first segment and re-encapsulates the packet in new L2
encapsulation headers for the next segment.
When an FHS Gateway receives a carrier packet with an OCH header that
must be forwarded to an LHS Gateway over the unsecured spanning tree,
it reconstructs the headers based on MFV 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 MFVI in the CRH-32 that will be meaningful to the LHS Gateway.
When the LHS Gateway receives the carrier packet, it locates the MFV
for the next hop based on the CRH-32 MFVI then re-applies header
compression (resulting in the removal of the CRH-32) and forwards the
carrier packet to the next hop.
3.7. OMNI Interface Decapsulation
OMNI interfaces (acting as OAL destinations) decapsulate and
reassemble OAL packets into original IP packets destined either to
the AERO node itself or to a destination reached via an interface
other than the OMNI interface the original IP packet was received on.
When carrier packets containing OAL fragments addressed to itself
arrive, this OAL destination discards the NET encapsulation headers
and reassembles to obtain the OAL packet or super-packet (see:
[I-D.templin-6man-omni]). The OAL destination then verifies the OAL
checksum, discards the OAL encapsulations to obtain the original IP
packet(s) and finally forwards them to either the network layer or a
next-hop on the OMNI link.
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3.8. OMNI Interface Data Origin Authentication
AERO nodes employ simple data origin authentication procedures. In
particular:
* AERO Gateways and Proxy/Servers accept carrier packets received
from the secured spanning tree.
* AERO Proxy/Servers and Clients accept carrier packets and original
IP packets that originate from within the same secured ANET.
* AERO Clients and Relays accept original IP packets from downstream
network correspondents based on ingress filtering.
* AERO Hosts, Clients, Relays, Proxy/Servers and Gateways verify
carrier packet L2 encapsulation addresses according to
[I-D.templin-6man-omni].
* AERO nodes accept carrier packets addressed to themselves with
Identification values within the current window for the OAL source
neighbor and drop any carrier packets with out-of-window
Identification values. (AERO nodes may forward carrier packets
not addressed to themselves without verifying the Identification
value.)
AERO nodes silently drop any packets that do not satisfy the above
data origin authentication procedures. Further security
considerations are discussed in Section 6.
3.9. 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).
The functions of the OAL and OMNI interface MTU/MRU/MPS
considerations are specified in [I-D.templin-6man-omni]. (Note that
the OMNI interface accommodates an assured MTU of 65535 octets due to
the use of fragmentation, and can optionally expose larger MTUs to
upper layers for best-effort Jumbogram services.)
When the network layer presents an original IP packet to the OMNI
interface, the OAL source encapsulates and fragments the original IP
packet if necessary. When the network layer presents the OMNI
interface with multiple original IP packets bound to the same OAL
destination, the OAL source can concatenate them as a single OAL
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super-packet as discussed in [I-D.templin-6man-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 3.10.4), 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.
3.10. OMNI Interface Forwarding Algorithm
Original IP packets enter a node's OMNI interface either from the
network layer (i.e., from a local application or the IP forwarding
system) while carrier packets enter from the link layer (i.e., from
an OMNI interface neighbor). All original IP packets and carrier
packets entering a node's OMNI interface first undergo data origin
authentication as discussed in Section 3.8. Those that satisfy data
origin authentication are processed further, while all others are
dropped silently.
Original IP packets that enter the OMNI interface from the network
layer are forwarded to an OMNI interface neighbor using OAL
encapsulation and fragmentation to produce carrier packets for
transmission over underlay interfaces. (If routing indicates that
the original IP packet should instead be forwarded back to the
network layer, the packet is dropped to avoid looping). Carrier
packets that enter the OMNI interface from the link layer are either
re-encapsulated and re-admitted into the OMNI link, or reassembled
and forwarded to the network layer where they are subject to either
local delivery or IP forwarding. In all cases, the OAL MUST NOT
decrement the original IP packet TTL/Hop-count since its forwarding
actions occur below the network layer.
OMNI interfaces may have multiple underlay interfaces and/or neighbor
cache entries for neighbors with multiple underlay interfaces (see
Section 3.3). The OAL uses Interface Attributes and/or Traffic
Selectors (e.g., port numbers, flow specifications, etc.) 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 underlay interfaces. AERO implementations SHOULD permit
network management to dynamically adjust Traffic Selector values at
runtime.
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If an OAL packet matches the Traffic Selectors of multiple outgoing
interfaces and/or neighbor interfaces, the OMNI interface replicates
the packet and sends one copy via each of the (outgoing / neighbor)
interface pairs; otherwise, it sends a single copy of the OAL packet
via an interface with the best matching Traffic Selector. (While not
strictly required, the likelihood of successful reassembly may
improve when the OMNI interface sends all fragments of the same
fragmented OAL packet 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.
The Subnet ID value in ULAs is used only for subnet coordination
within a local OMNI link segment. When a node forwards a packet with
a ULA with a foreign Global and/or Subnet ID value it forwards the
packet based solely on the OMNI link routing information. For this
reason, OMNI link routing and forwarding table entries always include
both ULAs 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 forwarding
algorithms for Hosts, Clients, Proxy/Servers and Gateways. In the
following discussion, an original IP packet's destination address is
said to "match" if it is the same as a cached address, or if it is
covered by a cached prefix (which may be encoded in a ULA-MNP).
3.10.1. Host Forwarding Algorithm
When an original IP packet 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 L2
encapsulation, fragments the encapsulated packet if necessary and
forwards the packets into the ENET addressed to the L2 address of the
neighbor.
After sending a packet, the Host may receive a 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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3.10.2. Client Forwarding Algorithm
When an original IP packet 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 on 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 invokes address resolution and multilink
forwarding procedures per Section 3.13. If there is a matching NCE
on an ENET interface (i.e., a downstream interface), the Client
instead performs OAL and/or L2 encapsulation and forwards the packet
to the downstream Host or Client.
When a carrier packet enters a Client's OMNI interface from the link-
layer, 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 this OAL source, then reassembles and
decapsulates as necessary and delivers the original IP packet to the
network layer. If the OAL destination matches a NCE for a Host or
Client on an ENET interface, the Client instead forwards the carrier
packet to the Host/Client. If the OAL destination does not match,
the Client drops the original IP packet and MAY return a network-
layer ICMP Destination Unreachable message subject to rate limiting
(see: Section 3.11).
When a Client forwards a carrier packet from an ENET Host to a
neighbor connected to the same ENET, it also returns a Redirect
message to inform the source 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 over ANET underlay interfaces without
invoking the OAL, since the ANET is secured at the link and physical
layers. By forwarding original IP packets without invoking the OAL,
however, the ANET peers can engage only in classical path MTU
discovery since the packets are subject to loss and/or corruption due
to the various per-link MTU limitations that may occur within the
ANET. Moreover, the original IP packets do not include either the
OAL integrity check or per-packet Identification values that can be
used for data origin authentication and link-layer retransmissions.
The tradeoff therefore involves an assessment of the per-packet
encapsulation overhead saved by bypassing the OAL vs. inheritance of
classical network "brittleness". (Note however that ANET peers can
send small original IP packets without invoking the OAL, while
invoking the OAL for larger packets. This presents the beneficial
aspects of both small packet efficiency and large packet robustness,
with delay variance and reordering as possible side effects.)
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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 MFVI information by examining the
MNP-based addresses in the actual IP packet 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.
3.10.3. Proxy/Server and Relay Forwarding Algorithm
When a Proxy/Server receives an original IP packet from the network
layer, it drops the packet if routing indicates that it should be
forwarded back to the network layer to avoid looping. Otherwise, the
Proxy/Server regards the original IP packet the same as if it had
arrived as carrier packets with OAL destination set to its own ULA.
When the Proxy/Server receives carrier packets on underlay interfaces
with OAL destination set to its own ULA, it performs OAL reassembly
if necessary to obtain the original IP packet. The Proxy/Server then
supports multilink forwarding procedures as specified in
Section 3.13.2 and/or acts as an ARS to initiate address resolution
as specified in Section 3.13.
When the Proxy/Server receives a carrier packet with OAL destination
set to a ULA-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 routing table entry for a GUA route that matches the
ULA-MNP. If there is no route, the Proxy/Server drops the carrier
packet; otherwise, it reassembles and decapsulates to obtain the
original IP packet then acts as a Relay to present it to the network
layer where it will be delivered according to standard IP forwarding.
When a Proxy/Server receives a carrier packet from one of its Client
neighbors with OAL destination set to another node, it forwards the
packets via a matching NCE or via the spanning tree if there is no
matching entry. When the Proxy/Server receives a carrier packet with
OAL destination set to a ULA-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, then re-encapsulates the carrier packet
and forwards it to a Gateway which will eventually deliver it to the
new Proxy/Server. If the neighbor cache state for the Client is
REACHABLE, the Proxy/Server forwards the carrier packets to the
Client which then must reassemble. (Note that the Proxy/Server does
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not reassemble carrier packets not explicitly addressed to its own
ULA, since some of the carrier packets of the same original IP packet
could be forwarded through a different Proxy/Server.) In that case,
the Client may receive fragments from multiple Proxy/Servers, but
that can still be reassembled.
Proxy/Servers process carrier packets with OAL destinations that do
not match their ULA in the same manner as for traditional IP
forwarding within the OAL, i.e., nodes use IP forwarding to forward
packets not explicitly addressed to themselves. (Proxy/Servers
include a special case that accepts and reassembles carrier packets
destined to a ULA-MNP of one of their Clients received over the
secured spanning tree.) Proxy/Servers process carrier packets with
their ULA as the destination by first examining the packet for a
CRH-32 header or an OCH header. In that case, the Proxy/Server
examines the next MFVI in the carrier packet to locate the MFV entry
in the MFIB for next hop forwarding (i.e., without examining IP
addresses). When the Proxy/Server forwards the carrier packet, it
changes the destination address according to the MFVI value for the
next hop found either in the CRH-32 header or in the node's own MFIB.
Proxy/Servers must verify that the L2 addresses of carrier packets
not received from the secured spanning tree are "trusted" before
forwarding according to an MFV (otherwise, the carrier packet must be
dropped).
Note: Proxy/Servers may receive carrier packets addressed to their
own ULA with CRH-32s that include additional forwarding information.
Proxy/Servers use the forwarding information to determine the correct
NCE and underlay interface for forwarding to the target Client, then
remove the CRH-32 and forward the carrier packet. If necessary, the
Proxy/Server reassembles first before re-encapsulating (and possibly
also re-fragmenting) then forwards to the target Client.
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Note: Clients and their FHS Proxy/Server peers can exchange original
IP packets over ANET underlay interfaces without invoking the OAL,
since the ANET is secured at the link and physical layers. By
forwarding original IP packets without invoking the OAL, however, the
Client and Proxy/Server can engage only in classical path MTU
discovery since the packets are subject to loss and/or corruption due
to the various per-link MTU limitations that may occur within the
ANET. Moreover, the original IP packets do not include either the
OAL integrity check or per-packet Identification values that can be
used for data origin authentication and link-layer retransmissions.
The tradeoff therefore involves an assessment of the per-packet
encapsulation overhead saved by bypassing the OAL vs. inheritance of
classical network "brittleness". (Note however that ANET peers can
send small original IP packets without invoking the OAL, while
invoking the OAL for larger packets. This presents the beneficial
aspects of both small packet efficiency and large packet robustness.)
Note: When a Proxy/Server receives a (non-OAL) original IP packet
from an ANET Client, or a carrier packet with OAL destination set to
its own ULA from any Client, the Proxy/Server reassembles if
necessary then performs ARS functions on behalf of the Client. The
Client may at some later time begin sending carrier packets to the
OAL address of the actual target instead of the Proxy/Server, at
which point it may begin functioning as an ARS on its own behalf and
thereby "override" the Proxy/Server's ARS role.
Note; Proxy/Servers drop any original IP packets (received either
directly from an ANET Client or following reassembly of carrier
packets received from an ANET/INET Client) with a destination that
corresponds to the Client's delegated MNP. Similarly, Proxy/Servers
drop any carrier packet received with both a source and destination
that correspond to the Client's delegated MNP regardless of their
OMNI link point of origin. These checks are necessary to prevent
Clients from either accidentally or intentionally establishing
endless loops that could congest Proxy/Servers and/or ANET/INET
links.
Note: Proxy/Servers forward secure control plane carrier packets via
the SRT secured spanning tree and forward other carrier packets 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 upper 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 unsecured message toward the destination which
must apply data origin authentication on its own behalf.
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Note: If the Proxy/Server has multiple original IP packets to send to
the same neighbor, it can concatenate them in a single OAL super-
packet [I-D.templin-6man-omni].
3.10.4. Gateway Forwarding Algorithm
Gateways forward spanning tree carrier packets while decrementing the
OAL header Hop Count but not the original IP header Hop Count/TTL.
Gateways convey carrier packets that encapsulate critical IPv6 ND
control messages or routing protocol control messages via the SRT
secured spanning tree, and may convey other carrier packets via the
secured/unsecured spanning tree or via more direct paths according to
MFIB information. When the Gateway receives a carrier packet, it
removes the L2 headers and searches for an MFIB entry that matches an
MFVI or an IP forwarding table entry that matches the OAL destination
address.
Gateways process carrier packets 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., nodes
use IP forwarding to forward packets not explicitly addressed to
themselves. Gateways process carrier packets with their ULA or the
SRT Subnet Router Anycast address as the OAL destination by first
examining the packet for a full OAL header with a CRH-32 extension or
an OCH header. In that case, the Gateway examines the next MFVI in
the carrier packet to locate the MFV entry in the MFIB for next hop
forwarding (i.e., without examining IP addresses). When the Gateway
forwards the carrier packet, it changes the OAL destination address
according to the MFVI value for the next hop found either in the
CRH-32 header or in the node's own MFIB. 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 directly to
the target Client while using the final hop MFVI instead of the next
hop (see: Section 3.13.4).
Gateways forward carrier packets received from a first segment via
the secured spanning tree to the next segment also via the secured
spanning tree. Gateways forward carrier packets received from a
first segment via the unsecured spanning tree to the next segment
also via the unsecured spanning tree. Gateways use 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).
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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 MFV (otherwise, the
carrier packet must be dropped).
3.11. OMNI Interface Error Handling
When an AERO node admits an original IP packet into the OMNI
interface, it may receive link-layer 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 3.9, 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
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:
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
| 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 headers |
| (first-fragment only) | i
~ ~ n
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~ e
| Portion of the body of | r
| the original IP packet | r
| (all fragments) | o
~ ~ r
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ---
Figure 4: OMNI Interface Link-Layer Error Message Format
The AERO node rules for processing these link-layer error messages
are as follows:
* When an AERO node receives a link-layer Parameter Problem message,
it processes the message the same as described as for ordinary
ICMP errors in the normative references [RFC0792][RFC4443].
* 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 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 3.15.5.
* 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 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 reassembly is
currently congested, it returns an OMNI interface Packet Too Big
(PTB) message as discussed in [I-D.templin-6man-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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3.12. AERO Mobility Service Coordination
AERO nodes observes the Router Discovery and Prefix Registration
specifications found in Section 15 of [I-D.templin-6man-omni]. AERO
nodes further coordinate their autoconfiguration actions with the
mobility service as discussed in the following sections.
3.12.1. 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-6man-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.
3.12.2. 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 layer 2 data link 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-6man-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 3.12.3) 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 option
with a prefix release indication (i.e., by setting the OMNI Neighbor
Coordination sub-option Preflen to 0). 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.)
3.12.3. 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-6man-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 3.2.3). 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 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 packets sent while route
optimization is in progress. The Hub Proxy/Server reassembles, then
re-encapsulates/re-fragments and forwards the 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 carrier
packets 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.
3.12.3.1. 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 {UAL,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 Neighbor Coordination sub-option window synchronization
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, 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 omIndex. Hub Proxy/Server "A" then prepares an RA
message with source set to its own ULA and destination set to the
source of the RS message, 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 "B". Hub Proxy/Server "A" then 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, 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-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.
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* 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 with OAL 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 carrier packets destined to a
neighbor cache target directly to the target according to the OAL/
link-layer information - the process of establishing neighbor cache
entries is specified in Section 3.13.
While the Client is still associated with FHS Proxy/Servers "B", "C",
"D", etc., each FHS Proxy/Server can send NS, RS and/or unsolicited
NA 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 interface 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 carrier packets 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 destined to the former
Client.
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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 without invoking the OAL so that the ANET
routing system transports the original IP packets 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-6man-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 or authentication signature is
invalidated, and a new checksum or authentication signature must be
calculated and included.
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 3.13.
3.12.3.2. 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 similar fashion as for 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(NUD) control messaging is carried only
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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(NUD) exchanges with the
Hub Proxy/Server, e.g., one exchange per second. The FHS Proxy/
Server sends the NS(NUD) 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(NUD). 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(NUD) 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 one of its other FHS Proxy/Servers to assume the Hub role
(i.e., by sending an RS with destination set to the ULA of the new
Hub).
3.12.3.3. 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.
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
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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 the
DHCPv6-PD Reply message and OMNI Neighbor Coordination sub-option
Preflen 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-6man-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-6man-omni] for further details.
3.13. AERO Address Resolution, Multilink Forwarding and Route
Optimization
AERO nodes invoke address resolution, multilink forwarding and route
optimization when they need to forward initial packets to new target
neighbors over ANET/INET interfaces and for ongoing multilink
forwarding for current target 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 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.
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* 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 current, consistent and
authentic. The ARS is responsible for periodically refreshing the
address resolution, and the ARR is responsible for quickly informing
the ARS of any changes. Following address resolution, the ARS and
ART perform continuous unicast multilink route optimization exchanges
to maintain optimal forwarding profiles.
The address resolution and route optimization procedures are
specified in the following sections.
3.13.1. Multilink Address Resolution
When one or more original IP packets 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 forwards 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 next prepares an NS message for Address Resolution (NS(AR))
to send toward an ART while including the original IP packet(s) as
trailing data following the NS(AR) in an OAL super-packet
[I-D.templin-6man-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's destination as
the Target Address, e.g., for 2001:db8:1:2::10:2000 the Target
Address is fd00::2001:db8:1:2.
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* the Solicited-Node multicast address [RFC4291] formed from the
lower 24 bits of the original IP packet'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 and with an OMNI Neighbor
Coordination sub-option with Preflen set to the prefix length
associated with the NS(AR) source. The ARS also includes Interface
Attributes and Traffic Selectors for all of the source Client's
underlay interfaces, calculates the authentication signature or
checksum, then selects an Identification value and submits the NS(AR)
message for OAL encapsulation with OAL source set to its own ULA and
OAL destination set to the XLA-MNP corresponding to the ART and with
window synchronization parameters. The ARS then 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 reassembles,
verifies the NS(AR) authentication signature or checksum, changes the
OAL source to its own ULA, changes the OAL destination to the XLA-MNP
corresponding to the ART, selects an appropriate Identification,
calculates the OAL checksum, then re-fragments and forwards the
resulting carrier packets into the secured spanning tree on behalf of
the Client.
Note: both the ART Client/Relay and its Hub Proxy/Server include
current and accurate information for the ART's multilink Interface
Attributes profile. The Hub Proxy/Server can be trusted to provide
an authoritative ARR response on behalf of the ART should the need
arise. While the ART has no such trust basis, any attempt by the ART
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 ART
itself. Therefore, the ART's asserted Interface Attributes need not
be validated by the Hub Proxy/Server.
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3.13.1.1. Relaying the NS(AR)
When the 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 destination
address. The Gateway then decrements the OAL header Hop-Limit, then
includes new L2 headers and forwards 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.
3.13.1.2. Processing and Responding to the NS(AR)
When the Hub Proxy/Server for 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, reassembles, verifies the OAL checksum
then either forwards the NS(AR) to the ART or processes it locally if
it is acting as a Relay/IP router or the ART's designated ARR. The
Hub Proxy/Server processes the message as follows:
* 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 recalculates the OAL checksum, re-fragments, includes
appropriate L2 headers then forwards the resulting carrier packets
over the secured spanning tree.
* if the Hub Proxy/Server is the ART's designated ARR, it prepares
to return an NA(AR) as discussed below; otherwise it continues
processing.
* 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;
otherwise, it must verify the message authentication signature.
Next, the Hub Proxy/Server determines the underlay interface for
the ART and proceeds as follows:
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- 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
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
includes a suitable Identification value, recalculates the OAL
checksum, re-fragments if necessary, includes appropriate L2
headers and forwards the resulting carrier packets over the
secured spanning tree.
- When the FHS Proxy/Server receives the carrier packets, it
reassembles and verifies the OAL and NS(AR) checksums, then
changes the OAL source to its own ULA and OAL destination to
the ULA-MNP of the ART. The FHS Proxy/Server next includes a
suitable Identification value, recalculates the OAL checksum,
re-fragments if necessary, includes appropriate L2 headers and
forwards the resulting carrier packets over the underlay
interface to the ART.
- 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
instead proceeds exactly as for the FHS Proxy/Server
instructions above.
* If the NS(AR) target matches one of its non-MNP routes, the Hub
Proxy/Server serves as both a Relay and a ARR, since the Relay
forwards IP packets toward the (fixed network) target at the
network layer.
The ARR then creates a NCE for the NS(AR) source address if
necessary, processes the window synchronization parameters, caches
all Interface Attributes and Traffic Selector information, and
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 includes
an OMNI option with OMNI Neighbor Coordination sub-option Preflen set
to the prefix length associated with the NA(AR) source address.
The ARR then includes Interface Attributes and Traffic Selector sub-
options for all of the ART's underlay interfaces with current
information for each interface. The ARR also includes either an
authentication signature or an NA message checksum as necessary. 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 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, selects an
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appropriate Identification, and includes window synchronization
parameters and authentication signature or checksum. , calculates the
OAL checksum, fragments, then includes appropriate L2 headers and
forwards the resulting (L2-encapsulated) carrier packets.
When the FHS Proxy/Server receives the carrier packets sent by an ART
acting as an ARR on its own behalf, it reassembles if necessary,
verifies the authentication signature or checksum and includes a new
authentication signature or checksum. The FHS Proxy/Server then
changes the OAL source address to its own ULA, changes the OAL
destination to the ULA corresponding to the NA(AR) destination,
includes an appropriate Identification, recalculates the NA and OAL
checksums and fragments if necessary. The FHS Proxy/Server finally
includes appropriate L2 headers and forwards the carrier packets into
the secured spanning tree.
Note: If the Hub Proxy/Server is acting as the target's ARR but not
as a Relay/IP router, it prepares the NA(AR) with the R flag set to 0
but without setting the SYN/ACK flags in the OMNI Neighbor
Coordination sub-option window synchronization parameters. This
informs the ARS that it must initiate multilink route optimization to
synchronize with the target either directly or via an LHS Proxy/
Server (see: Section 3.13.2). In all other ways, the Hub Proxy/
Server prepares and returns the NA(AR) the same as for the FHS Proxy/
Server case above.
3.13.1.3. Relaying the NA(AR)
When the 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
secured spanning tree to a Proxy/Server for the ARS.
3.13.1.4. Processing the NA(AR)
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 all Interface Attributes), and caches the NA(AR)
XLA source address as the address of the ART.
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When the ARS is a Client, the SRT secured spanning tree will first
deliver the solicited NA(AR) message to the FHS Proxy/Server, which
re-encapsulates 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).
3.13.2. Multilink Forwarding
Following address resolution, the ARS and ART can assert multilink
forwarding paths through underlay interface pairs serviced by the
same source/destination ULAs by sending unicast NS/NA messages with
OMNI Multilink Forwarding Parameter (MFP) and/or Neighbor
Coordination 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.
Nodes that configure OMNI interfaces include an additional forwarding
table termed the Multilink Forwarding Information Base (MFIB) that
supports carrier packet forwarding based on OMNI neighbor underlay
interface pairs. The MFIB contains Multilink Forwarding Vectors
(MFVs) identified by locally-unique 4-octet values known as MFV
Indexes (MFVIs). The MVFs cache uncompressed OAL header information
as well as the previous/next-hop addressing and MFVI information.
OAL source, intermediate and target nodes create MFVs/MFVIs when they
process an NS message with an MFP 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-6man-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)".
When an OAL node initiates or forwards an NS with Job code '00', it
creates an MFV, records the NS source and destination ULAs then
generates and assigns a locally-unique "B" MFVI (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 carrier packets that
include "B", it can unambiguously locate the correct MFV and
determine directionality without examining addresses. When the MFV
is indexed by its "B" MFVI, it returns the ULAs in (dst,src) order
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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" MFVI to locate the MFV created by the NS then
generates and assigns a locally-unique "A" MFVI (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 MFV and
determine directionality without examining addresses. When the MFV
is indexed by its "A" MFVI, 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 MFVIs
which must first be tested for local uniqueness. If a candidate MFVI
s already in use, the OAL node repeats the random generation process
until it obtains a unique non-zero value. Since the number of MFVs
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 MFVI
locally generated by a first OAL node must not be tested for
uniqueness by other OAL nodes.
OAL nodes cache MFVs for up to ReachableTime seconds following their
initial creation. If the node processes another NS or NA message
specific to an MFV, it resets ReachableTime to REACHABLE_TIME
seconds, i.e., the same as for NCEs. If ReachableTime expires, the
node deletes the MFV and frees its associated MFVIs so they can be
reused for future MFVs.
The following sections provide the detailed specifications of these
NS/NA exchanges for all nodes along the forward and reverse paths.
3.13.2.1. FHS Client-Proxy/Server NS Forwarding
When an FHS OAL source has an original IP packet to send to an LHS
OAL target following multilink address resolution, it first selects a
source and target underlay interface pair. The FHS source uses its
cached information for the target underlay interface as LHS
information then prepares an NS message with an MFP sub-option with
Job code '00' and with the NS source set to its own ULA or XLA and
the NS destination set to the ULA or XLA of the LHS target. The FHS
source then sets window synchronization information in the OMNI
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Neighbor Coordination sub-option and creates a NCE for the selected
target ULA or XLA in the INCOMPLETE state. The FHS source next
creates an MFV then generates and assigns a locally-unique "B" MFVI
to the MFV while also including it as the first "B" entry in the MFP
MFVI List. The FHS source then includes any FHS/LHS addressing
information it knows locally in the MFP 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 code. If FMT-Forward is clear and FMT-Mode is set, the FHS
Proxy/Server checks for a NCE for the ULA of the LHS Proxy/Server.
If there is no NCE, the FHS Proxy/Server creates one in the
INCOMPLETE state. If a new NCE was created (or if the existing NCE
requires fresh window synchronization), the FHS Proxy/Server then
writes window synchronization parameters into the MFP Tunnel Window
Synchronization fields. 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 forwards 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 FHS FMT-Forward is set and
LHS FMT-Forward is clear, the FHS Client creates/updates a NCE for
the ULA of the LHS Proxy/Server as above and includes Tunnel Window
Synchronization parameters. The FHS Client then 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 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 forwards the carrier
packets to the FHS Proxy/Server.
When the FHS Proxy/Server receives the carrier packets, it verifies
the Identification then reassembles to obtain the NS, verifies the
OAL checksum and verifies the NS authentication signature or
checksum. The FHS Proxy/Server then creates an MFV (i.e., the same
as the FHS Client had done) while caching the MFP MFVI List "B" entry
along with the FHS Client addressing information as previous hop
information for this MVF. The FHS Proxy/Server next generates a new
locally-unique "B" MFVI, then both assigns it as the MFV index and
writes it as the next "B" entry in the MFP MFVI List (while also
writing any FHS Client and Proxy/Server addressing information). The
FHS Proxy/Server then checks FHS/LHS FMT-Forward/Mode to determine
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whether to create a NCE for the LHS Proxy/Server ULA and include
Tunnel Window Synchronization parameters the same as above. 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 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 forwards the carrier
packets into the secured spanning tree.
3.13.2.2. Gateway NS Forwarding
Gateways in the spanning tree forward carrier packets 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 a carrier packet 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 MFV (i.e., the same as
the FHS Proxy/Server had done) while caching the MFP FHS Client and
Proxy/Server addressing information and corresponding MFVI List "B"
list values in the MFV to enable future reverse path forwarding to
this FHS Client. The FHS Gateway then generates a locally-unique "B"
MFVI for the MFV and also writes it as the next "B" entry in the NS
MFP MFVI 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 MFP LHS information in
the MFV, writes its LHS ULA and INADDR into the NS MFP 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
and the LHS Subnet Router Anycast ULA as the OAL destination. The
FHS Gateway then selects an appropriate Identification, recalculates
the NS and OAL checksums, re-fragments if necessary, then finally
includes appropriate L2 headers and forwards 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 carrier packets
without further processing. The LHS Gateway then reassembles to
obtain the NS, verifies the OAL and NS checksums then creates an MFV
(i.e., the same as the FHS Gateway had done) while caching the MFP
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"B" MFVIs and addressing information of previous OAL forwarding hops.
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" MFVI for the MFV.
The LHS Gateway then writes its own LHS ULA and INADDR into the MFP
sub-option while also writing "B" as the next entry in the MFP MFVI
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, selects an
appropriate Identification, recalculates the NS and OAL checksums,
re-fragments if necessary, then finally includes appropriate L2
headers and forwards the carrier packets into the secured spanning
tree.
3.13.2.3. LHS Proxy/Server-Client NS Receipt and NA Forwarding
When the LHS Proxy/Server receives the carrier packets from the
secured spanning tree, it reassembles to obtain the NS, 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
MFV and caches the MFP "B" MFVIs and addressing information of
previous OAL forwarding hops the same as for the prior hop. If the
NS destination is the XLA of the LHS Client, the LHS Proxy/Server
also generates a locally-unique "B" MFVI and assigns it both to the
MFVI and as the next "B" entry in the MFVI List. The LHS Proxy/
Server then examines FHS FMT; if FMT-Forward is clear and FMT-Mode is
set, the LHS Proxy/Server creates a NCE for the ULA of the FHS Proxy/
Server (if necessary) and sets the state to STALE, then caches any
Tunnel Window Synchronization parameters.
If the NS destination matches its own ULA, the LHS Proxy/Server next
prepares to return a solicited NA with Job code '01'. If the NS
source was the XLA of the FHS Client, the LHS Proxy/Server first
creates or updates an NCE for the XLA with state set to STALE. The
LHS Proxy/Server next caches the NS OMNI Neighbor Coordination sub-
option window synchronization parameters and MFP information
(including the MFVI List) in the NCE corresponding to the ULA source.
When the LHS Proxy/Server forwards future carrier packets based on
the NCE, it can populate forwarding information in a CRH-32 routing
header to enable forwarding based on the cached MFVI List "B" entries
instead of ULA addresses.
The LHS Proxy/Server then creates an NA with Job code '01' while
copying the NS MFP sub-option into the NA. The LHS Proxy/Server then
generates a locally-unique "A" MFVI and both assigns it to the MFV
and includes it as the first "A" entry in the MFP sub-option MFVI
List (see: [I-D.templin-6man-omni] for details on MFVI List A/B
processing). The LHS Proxy/Server then includes end-to-end window
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synchronization parameters in the OMNI Neighbor Coordination sub-
option (if necessary) and also tunnel window synchronization
parameters in the MFP sub-option (if necessary). The LHS Proxy/
Server then encapsulates the NA with the OAL source set to its own
ULA and the 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 instead includes an authentication signature in the NS if
necessary (otherwise recalculates the checksum), then 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 selects an appropriate
Identification value, calculates the OAL checksum, fragments if
necessary then finally includes appropriate L2 headers and forwards
the carrier packets to the LHS Client. When the LHS Client receives
the carrier packets, it verifies the Identification and reassembles
to obtain the NS then verifies the OAL checksum and NS authentication
signature or checksum. The LHS Client then creates a NCE for the NS
ULA source address in the STALE state and examines the MFP sub-
option. If LHS FMT-Forward is set, FHS FMT-Forward is clear and the
NS source was an XLA, the Client also creates a NCE for the ULA of
the FHS Proxy/Server in the STALE state and caches any Tunnel Window
Synchronization parameters. The Client then caches the NS OMNI
Neighbor Coordination and MFP sub-options in the NCE corresponding to
the NS ULA source, then creates an MFV, caches the addressing
information and "B" entries of the previous OAL hops then finally
generates and assigns a locally-unique "A" MFVI the same as for
previous hops.
The LHS Client then prepares an NA using exactly the same procedures
as for the LHS Proxy/Server above, 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 (otherwise
calculates the checksum), then encapsulates the NA with OAL source
set to its 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 forwards the carrier packets
to the LHS Proxy/Server. When the LHS Proxy/Server receives the
carrier packets, it verifies the Identifications, reassembles to
obtain the NA, verifies the OAL checksum and NA authentication
signature or checksum, then uses the current MFP MVFI List "B" entry
to locate the MFV. The LHS Proxy/Server then caches the addressing
and "A" information for the LHS Client in the MVF, then generates a
locally-unique "A" MFVI and both assigns it to the MFV and writes it
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as the next MFP MFVI List "A" entry. The LHS Proxy/Server then
examines the FHS/LHS FMT codes to determine if it needs to include
Tunnel Window Synchronization parameters. 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, includes an appropriate
Identification, calculates the OAL checksum, re-fragments if
necessary then finally includes appropriate L2 headers and forwards
the carrier packets into the secured spanning tree.
3.13.2.4. Gateway NA Forwarding
When the LHS Gateway receives the carrier packets containing the NA
message, it reassembles and verifies the OAL and NA checksums then
uses the current NA MFP MFVI List "B" entry to locate the MFV. The
LHS Gateway then caches the MFP addressing and MFVI List "A"
information for the previous hops in the MFV, then generates a
locally-unique "A" MFVI and both assigns it to the MFV and writes it
as the next MFP MFVI 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 selects an appropriate Identification,
recalculates the OAL checksum, re-fragments if necessary, includes
appropriate L2 headers and finally forwards 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
reassembles to obtain the NA, verifies the OAL and NA checksums and
locates the MFV based on the current MFP MFVI List "B" entry. The
FHS Gateway then caches the addressing and "A" information for the
previous hops in the MFV and generates a locally-unique "A" MVFI.
The FHS Gateway then assigns the new "A" value to the MVF, records
"A" in the MFP MFVI List then writes its FHS ULA and INADDR into the
MFP 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
selects an appropriate Identification value, recalculates the OAL
checksum, re-fragments if necessary, includes appropriate L2 headers
and finally forwards the carrier packets into the secured spanning
tree.
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3.13.2.5. FHS Proxy/Server-Client NA Receipt
When the FHS Proxy/Server receives the carrier packets from the
secured spanning tree, it reassembles to obtain the NA, verifies the
OAL and NA checksums then locates the MFV based on the current MFP
MFVI List "B" entry. The FHS Proxy/Server then caches the MFP
addressing and "A" information for the previous hops. If the NA
destination matches its own ULA, the FHS Proxy/Server then examines
LHS FMT. If FMT-Forward is clear, the FHS Proxy/Server locates the
NCE for the ULA of the LHS Proxy/Server and sets the state to
REACHABLE then caches any Tunnel Window Synchronization parameters.
If the NA source is the XLA of the LHS Client, the FHS Proxy/Server
then locates the LHS Client NCE and sets the state to REACHABLE then
caches the OMNI Neighbor Coordination 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 also searches for and updates the NCE for the ULA of the LHS
Proxy/Server if necessary the same as above. The FHS Proxy/Server
then generates a locally-unique "A" MFVI and assigns it both to the
MFV and as the next MFP MFVI List "A" entry, then includes an
authentication signature or 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 selects an appropriate Identification value, recalculates the
OAL checksum, re-fragments if necessary, includes appropriate L2
headers and finally forwards the carrier packets to the FHS Client.
When the FHS Client receives the carrier packets, it verifies the
Identification, reassembles to obtain the NA, verifies the OAL
checksum and NA authentication signature or checksum, then locates
the MFV based on the current MFP MFVI 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 examines LHS FMT. If FMT-
Forward is clear, the FHS Client locates the NCE for the ULA of the
LHS Proxy/Server and sets the state to REACHABLE then caches any
Tunnel Window Synchronization parameters. If the NA source is the
XLA of the LHS Client, the FHS Client then locates the LHS Client NCE
and sets the state to REACHABLE then caches the OMNI Neighbor
Coordination window synchronization parameters and prepares to return
an unsolicited NA (uNA) acknowledgement, if necessary.
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3.13.2.6. 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 MFP sub-option with Job code set to '10' (Follow A;
Record B) (note that this step is unnecessary when Rapid Commit route
optimization is used per Section 3.13.3). The FHS node sets the uNA
source to its own ULA or XLA, sets the uNA destination to the ULA or
XLA of the LHS node then includes Tunnel Window Synchronization
parameters if necessary. The FHS node next sets the MFP MFVI 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 or checksum, selects an appropriate
Identification value, calculates the OAL checksum, fragments if
necessary, includes appropriate L2 headers and finally forwards 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 authentication signature or checksum, then uses
the current MFVI List "A" entry to locate the MFV. The FHS Proxy/
Server then writes its "B" MFVI as the next MFP MFVI List "B" entry
and determines whether it needs to include Tunnel Window
Synchronization parameters the same as it had done when it forwarded
the original NS with Job code '00'.
The FHS Proxy/Server 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 selects an appropriate
Identification, recalculates the OAL checksum, includes appropriate
L2 headers and finally forwards the carrier packets into the secured
spanning tree. When the FHS Gateway receives the carrier packets, it
reassembles to obtain the uNA, verifies the OAL and uNA checksums
then uses the current MFVI List "A" entry to locate the MFV. The FHS
Gateway then writes its "B" MFVI as the next MFP MFVI 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
selects an appropriate Identification, recalculates the OAL checksum,
re-fragments if necessary, includes appropriate L2 headers and
finally forwards 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.
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When the LHS Proxy/Server receives the carrier packets, it
reassembles to obtain the uNA message then verifies the OAL and uNA
checksums. The LHS Proxy/Server then locates the MFV based on the
current MFP MFVI List "A" entry then determines whether it is a
tunnel ingress the same as for the original NS. If so, the LHS
Proxy/Server updates the NCE for the tunnel far-end based on the
Tunnel Window Synchronization parameters. If the uNA destination
matches its own ULA, the LHS Proxy/Server next updates the NCE for
the source ULA based on the OMNI Neighbor Coordination sub-option
window synchronization parameters and MAY compare the MVFI List to
the version it had cached in the MFV based on the original NS.
If the uNA destination is the XLA of the LHS Client, the LHS Proxy/
Server instead writes its "B" MFVI as the next MFP MFVI List "B"
entry and includes an authentication signature or 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 selects an appropriate
Identification and recalculates the OAL checksum. The LHS Proxy/
Server finally re-fragments if necessary, includes appropriate L2
headers and forwards the resulting carrier packets to the LHS Client.
When the LHS Client receives the carrier packets, it verifies the
Identification, reassembles to obtain the uNA, verifies the OAL
checksum and uNA authentication signature or checksum then processes
the message exactly the same as for the LHS Proxy/Server case above.
3.13.2.7. OAL End System Exchanges Following Synchronization
Following the initial NS/NA exchange with MFP sub-options, OAL end
systems and tunnel endpoints can begin exchanging ordinary carrier
packets that include "A/B" MFVIs 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 MFIBs when they
receive carrier packets that include "A/B" MFVIs to unambiguously
locate the correct MFV and can use any discovered "A/B" values of
other OAL nodes to forward carrier packets to nodes that configure
the corresponding MFVIs. 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 MFIB cache state in the path before
ReachableTime expires.
While the OAL end systems continue to actively exchange packets, they
are jointly responsible for updating cache state and per-interface
reachability before expiration. Window synchronization state is
shared by all underlay interfaces in the FHS peer's NCE that use the
same destination ULA so that a single NS/NA exchange applies for all
interfaces regardless of the specific interface used to conduct the
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exchange. However, the window synchronization exchange only confirms
target Client reachability over the specific underlay interface pair.
Reachability for other underlay interfaces that share the same window
synchronization state must be determined individually using
additional NS/NA messages.
To update MFIB state in the path, the FHS node that sent the original
NS message with MFP Job code '00' can send additional NS messages
with Job code '10' (Follow "A"; Record "B"). The message will be
processed by all intermediate OAL nodes which will refresh MFV timers
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 MFP 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 MFP 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 MFIB 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 carrier packets with
a list of "A/B" MFVIs that OAL intermediate nodes can use for
shortest-path carrier packet forwarding based on MFVIs instead of
spanning tree addresses. OAL sources and intermediate nodes can
instead forward carrier packets with OAL compressed headers termed
"OCH" (see: [I-D.templin-6man-omni]) that include only a single "A/B"
MFVI meaningful to the next hop, since all OAL nodes in the path up
to (and sometimes including) the OAL destination have already
established MFVs. Note that when an FHS OAL source receives a
solicited NA with Job code '01', the MFP sub-option will contain an
MFVI 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 MFP MFVI 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.
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When a Gateway receives unsecured carrier packets destined to a local
SRT segment Client that has asserted direct reachability, the Gateway
performs direct carrier packet forwarding while bypassing the local
Proxy/Server based on the Client's advertised MFVIs and discovered
NATed INADDR information (see: Section 3.13.4). If the Client cannot
be reached directly (or if NAT traversal has not yet converged), the
Gateway instead forwards carrier packets directly to the local
segment Proxy/Server.
When a Proxy/Server receives carrier packets destined to a local SRT
segment Client or forwards carrier packets received from a local
segment Client, it first locates the correct MFV. If the carrier
packets include a secured IPv6 ND message, the Proxy/Server uses the
Client's NCE established through RS/RA exchanges to re-encapsulate/
re-fragment while forwarding outbound secured carrier packets via the
secured spanning tree and forwarding inbound secured carrier packets
while including an authentication signature or checksum. For
ordinary carrier packets, the Proxy/Server uses the same MFV if
directed by MFVI and/or OAL addressing. Otherwise it locates an MFV
established through an NS/NA exchange between the Client and the
remote SRT segment peer, and forwards the carrier packets without
first reassembling/decapsulating.
When a Proxy/Server or Client configured as a tunnel ingress receives
a carrier packet with a full OAL header with a ULA-MNP source and
CRH-32 routing header, or an OCH header with an MFVI that matches an
MFV, the ingress encapsulates the carrier packet in a new full OAL
header or an OCH header containing the next hop MVFI and an
Identification value appropriate for the end-to-end window and the
outer header containing an Identification value appropriate for the
tunnel endpoints. When a Proxy/Server or Client configured as a
tunnel egress receives an encapsulated carrier packet, it verifies
the Identification in the outer header, then discards the outer
header and forwards the inner carrier packet to the final
destination.
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When a Proxy/Server with FMT-Forward/Mode set to 0/1 for a source
Client receives carrier packets from the source Client, it first
reassembles to obtain the original OAL packet then re-fragments if
necessary to cause the Client's packets to fit within the MPS on the
path from the Proxy/Server as a tunnel ingress to the tunnel egress.
The Proxy/Server then performs OAL-in-OAL encapsulation and forwards
the resulting carrier packets to the tunnel egress. When a Proxy/
Server with FMT-Forward/Mode set to 0/1 for a target Client receives
carrier packets from a tunnel ingress, it first decapsulates to
obtain the original fragments then reassembles to obtain the original
OAL packet. The Proxy/Server then re-fragments if necessary to cause
the fragments to match the target Client's underlay interface (Path)
MTU and forwards the resulting carrier packets to the target Client.
When a source Client forwards carrier packets it can employ header
compression according to the MFVIs established through an NS/NA
exchange with a remote or local peer. When the source Client
forwards to a remote peer, it can forward carrier packets to a local
SRT Gateway (following the establishment of INADDR information) while
bypassing the Proxy/Server following route optimization (see:
Section 3.13.4). When a target Client receives carrier packets that
match a local MFV, 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 IP packet to
upper layers.
When synchronized peer Clients in the same SRT segment with FMT-
Forward and FMT-Mode set discover each other's NATed INADDR
addresses, they can exchange carrier packets directly with header
compression using MFVIs discovered as above (see: Section 3.13.5).
The FHS Client will have cached the "A" MFVI for the LHS Client,
which will have cached the "B" MVFI for the FHS Client.
3.13.3. Rapid Commit Route Optimization
When the LHS peer receives an NS(AR) with a set of Interface
Attributes for the source Client, it can perform "rapid commit" by
immediately invoking multilink route optimization as above instead of
returning an NA(AR). In order to perform rapid commit, the LHS peer
prepares a unicast NS message with an OMNI option with window
synchronization information responsive to the NS(AR), with an MFP
sub-option selected for a specific underlay interface pair and with
Interface Attributes for all of the LHS peer's other underlay
interfaces. The LHS peer can also include ordinary IP packets as OAL
super-packet extensions to the NS message if it has immediate data to
send to the FHS peer. The LHS peer then returns the NS to the FHS
peer the same as for the NA(AR) case.
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When the NS message traverses the return path to the FHS peer, all
intermediate nodes in the path establish state exactly the same as
for an ordinary NS/NA multilink route optimization exchange. When
the NS message arrives at the FHS peer, the window synchronization
parameters confirm that the NS is taking the place of the NA(AR),
thereby eliminating an extraneous message transmission and associated
delay. The FHS peer then completes the route optimization by
returning a responsive NA.
Note: The LHS peer must accept unicast NS messages with an ACK
matching the SYN included in the NS(AR) as an equivalent message
replacement for the NA(AR). Address resolution and multilink
forwarding coordination can therefore be coordinated in a single
three-way handshake connection with minimal messaging and delay
(i.e., as opposed to a four-message exchange).
3.13.4. 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.
When the Gateway receives the carrier packet, it verifies the
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 omIndex, 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.
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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 forwarding 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 forwards a carrier packet with an MFVI
toward the Gateway as the next hop, the Client uses the MFVI for the
Gateway (discovered during multilink route optimization) instead of
the MFVI for its Proxy/Server; the Gateway will accept the packet
from the Client if and only if the MFVI matches the correct MFV 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.)
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
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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.
3.13.5. 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 forwarding 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 MFIB state, they also include an Origin
Indication (i.e., in addition to an MFP sub-option) with the mapped
addresses discovered during the RS/RA exchanges with their respective
Proxy/Servers. After the MFV paths have been established, both
Clients can begin sending packets via strict MFV 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 packets
from that L2 address (see: [RFC4380] and [I-D.templin-6man-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 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 and encapsulates in L2 headers addressed
to its Proxy/Server then forwards the resulting carrier packets to
the Proxy/Server.
When the Proxy/Server receives the carrier packets, it re-
encapsulates and forwards them as unsecured carrier packets according
to MFIB 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
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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. While the Clients continue to
exchange carrier 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.
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.
3.13.6. Client-to-Client OMNI Link Extension
Clients may be recursively nested within the ENETs of other Clients.
When a Client is the downstream-attached ENET neighbor of an upstream
Client, it still supports the route optimization functions discussed
above by maintaining an MFIB and assigning MFVI values. When the
Client processes an IPv6 ND NS/NA message that includes an MFP sub-
option, it writes its MFVI information as the first/last MFVI list
entry the same as for the single Client case discussed above.
The Client then forwards the NS/NA message to the next Client in the
extended OMNI link toward the FHS/LHS Proxy/Server, which records the
MVFI value then overwrites the MFVI list entry with its own MFVI
value. This process iteratively continues until the Client that will
forward the NS/NA message to the FHS/LHS Proxy/Server is reached, at
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which point the NS/NA MFVI list entries are populated by the
intermediate nodes on the path to the LHS/FHS the same as discussed
above.
In this way, each Client in the extended OMNI link discovers the A/B
MVFIs of the next/previous Client without intruding into the MFP sub-
option MFVI list. Therefore the list can remain fixed at 5 entries
even though the Client-to-Client OMNI link extension can be
arbitrarily long. Therefore, route optimization is not possible
between consecutive Client members of the extended OMNI link but
becomes possible at the Internetworking border that separates the FHS
and LHS elements.
3.13.7. Intra-ANET/ENET Route Optimization for AERO Peers
When a Client forwards a packet 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].
In the same fashion, when a Proxy/Server forwards a packet 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.
3.14. Neighbor Unreachability Detection (NUD)
AERO nodes perform Neighbor Unreachability Detection (NUD) per
[RFC4861] either reactively in response to persistent link-layer
errors (see Section 3.11) 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(NUD) 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(NUD) messages use the unicast XLAs/ULAs of
the parties involved in the NUD test. When only reachability
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information is required without updating any other NCE state, AERO
nodes can instead perform NS/NA(NUD) exchanges directly between
neighbors without employing the secured spanning tree as long as they
include in-window Identifications and either an authentication
signature or checksum.
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(NUD) messages over the SRT secured or unsecured spanning tree, or
through NS(NUD) messages sent directly to an underlay interface of
the target itself. While testing a target underlay interface, the
source can optionally continue to forward carrier packets via
alternate interfaces, maintain a small queue of carrier packets until
target reachability is confirmed or include them as trailing data
with the NS(NUD) in an OAL super-packet [I-D.templin-6man-omni].
NS(NUD) messages are encapsulated, fragmented and transmitted as
carrier packets the same as for ordinary original IP data packets,
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(NUD) message the
same as described in Section 3.13.2 and includes an Interface
Attributes sub-option with omIndex set to identify its underlay
interface used for forwarding. The source then includes an in-window
Identification, fragments the OAL packet and forwards the resulting
carrier packets into the unsecured spanning tree, directly to the
target if it is in the local segment or directly to a Gateway in the
local segment.
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When the target receives the NS(NUD) carrier packets, it verifies
that it has a NCE for this source and that the Identification is in-
window, then submits the carrier packets for reassembly. The target
then verifies the authentication signature or checksum, then searches
for Interface Attributes in its NCE for the source that match the
NS(NUD) for the NA(NUD) reply. The target then prepares the NA(NUD)
with the source and destination addresses reversed, encapsulates and
sets the OAL source and destination, includes an Interface Attributes
sub-option in the NA(NUD) to identify the omIndex of the underlay
interface the NS(NUD) arrived on and sets the Target Address to the
same value included in the NS(NUD). 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 forwards the carrier packets into the unsecured spanning tree,
directly to the source if it is in the local segment or directly to a
Gateway in the local segment.
When the source receives the NA(NUD), 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.
3.15. 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.
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Mobility management considerations are specified in the following
sections.
3.15.1. Mobility Update Messaging
Hub Proxy/Servers (and/or the mobile Clients themselves) accommodate
mobility and/or multilink change events by sending secured uNA
messages to each of the Client's active neighbors. 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 Neighbor Coordination sub-option Preflen set to the
prefix length associated with the mobile Client's XLA, includes
Interface Attributes and Traffic Selectors 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 PNG flag in the uNA
OMNI option header to request a uNA acknowledgement as specified in
[I-D.templin-6man-omni].
When the FHS/LHS Proxy/Server receives a 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 PNG flag was set, the node that processes the uNA returns a
uNA acknowledgement as specified in [I-D.templin-6man-omni].
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3.15.2. Announcing Link-Layer Information Changes
When a Client needs to change its underlay Interface Attributes and/
or Traffic Selectors (e.g., due to a mobility event), the Client
sends an RS message to its Hub Proxy/Server (via a first-hop FHS
Proxy/Server, if necessary). The RS includes an OMNI option with an
Interface Attributes sub-option with the omIndex and with new link
quality and any other information.
Note that the first FHS Proxy/Server may change due to the underlay
interface change. If the Client supplies the address of the former
FHS Proxy/Server, the new FHS Proxy/Server can send a departure
indication (see below); otherwise, any stale state in the former FHS
Proxy/Server will simply expire after ReachableTime expires with no
effect on the Hub Proxy/Server.
Up to MAX_RTR_SOLICITATIONS RS messages MAY be sent in parallel with
sending carrier packets containing user data in case one or more RAs
are lost. If all RAs are lost, the Client SHOULD re-associate with a
new Proxy/Server.
After performing the RS/RA exchange, the Client sends uNA messages to
all neighbors the same as described in the previous section.
3.15.3. 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.
3.15.4. 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.
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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
omIndex 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.
3.15.5. Moving Between Proxy/Servers
The Client performs the procedures specified in Section 3.12.2 when
it first associates with a new Hub Proxy/Server or renews its
association with an existing Hub Proxy/Server.
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 OMNI Neighbor Coordination sub-option
Preflen set to 0. 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 and sends the carrier
packets via the secured spanning tree.
When the old Hub Proxy/Server receives the uNA, it 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. After
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 packets that would otherwise be lost due to the mobility event.
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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 gone unreachable,
topological movements of significant distance, movement to a new
geographic region, movement to a new OMNI link segment, etc.
3.16. Multicast
Clients provide an IGMP (IPv4) [RFC2236] or MLD (IPv6) [RFC3810]
proxy service for its ENETs and/or hosted applications [RFC4605] and
act 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 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 INET and ANET underlay
interfaces without native multicast services instead send NS(AR)
messages as an ARS to cause their FHS Proxy/Server forward the
message to an ARR. When the ARR receives 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.
3.16.1. 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 3.13) 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
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delivers it to ARR "Y" that services S. The resulting NA(AR) will
return 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 route optimization
exchange over the secured spanning tree while including a PIM Join/
Prune 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 3.15. 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.
3.16.2. 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 route
optimization 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.
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For each source S that sends multicast traffic to group G via R,
Client S* that aggregates S (or its Proxy/Server) encapsulates the
original IP packets in PIM Register messages, includes the PIM
Register messages in the OMNI options of uNA messages, performs OAL
encapsulation and fragmentation then forwards the resulting carrier
packets with Identification values within the receive window for
Client R* that aggregates R. 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; 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 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 3.16.1. Once the (S,G) tree is
established, the listeners can send (S, G) Prune messages to R so
that multicast original IP packets for group G sourced by S will only
be delivered via the (S, G) tree and not from the (*, G) tree rooted
at R. All mobility considerations discussed for SSM apply.
3.16.3. 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.
3.17. 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 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 3.2.4).
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The Client's IP 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 destined to a target via the correct OMNI link.
In a first alternative, if each OMNI link services different MSPs the
Client can receive a distinct MNP from each of the links. IP routing
will therefore assure that the correct OMNI link is used for both
outbound and inbound traffic. This can be accomplished using
existing technologies and approaches, and without requiring any
special supporting code in correspondent nodes or Gateways.
In a second alternative, if each OMNI link services the same MSP(s)
then each link could assign a distinct "OMNI link Anycast" address
that is configured by all Gateways on the link. Correspondent nodes
can then perform Segment Routing to select the correct SRT, which
will then direct the original IP packet over multiple hops to the
target.
3.18. 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 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.
3.19. 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
distributing its MNPs and/or discovering non-MNP IP GUA prefixes on
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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].
3.20. 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 deployments.
3.21. 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-6man-omni]) to be used as the Client ID seed for
MNP prefix delegation. The Client would then be obligated to
renumber its internal networks whenever its MNP (and therefore also
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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.
4. 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.
5. IANA Considerations
The IANA has assigned the UDP port number "8060" for an earlier
experimental first version of AERO [RFC6706]. This document together
with [I-D.templin-6man-omni] reclaims UDP port number "8060" as the
service port for UDP/IP encapsulation. This document makes no
request of IANA, since [I-D.templin-6man-omni] already provides
instructions. (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.
6. Security Considerations
AERO Gateways configure 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 [WG], etc. The AERO Gateways of all OMNI link
segments in turn configure secured tunnels for their neighboring AERO
Gateways 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.
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To prevent spoofing vectors, Proxy/Servers MUST discard without
responding to any unsecured NS/NA(AR) messages. Also, Proxy/Servers
MUST discard without forwarding any original IP packets received from
one of their own Clients (whether directly or following OAL
reassembly) with a source address that does not match the Client's
MNP and/or a destination address that does match the Client's MNP.
Finally, Proxy/Servers MUST discard without forwarding any carrier
packets with an OAL source and destination that both match the same
MNP.
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 secured tunnels, 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-6man-omni] to create a secured tunnel
on-demand, or to use the QUIC-TLS protocol to establish a secured
connection [RFC9000][RFC9001][RFC9002].
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 their
IPv6 ND messages as specified in [I-D.templin-6man-omni].
Application endpoints SHOULD use transport-layer (or higher-layer)
security services such as QUIC-TLS, TLS/SSL, DTLS or SSH [RFC4251] 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 Proxys and 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.
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
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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 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 layer 2 data link 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
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-6man-omni]. In environments where spoofing
is considered a threat, OAL nodes SHOULD employ Identification window
synchronization and OAL destinations SHOULD configure an (end-system-
based) firewall.
SRH authentication facilities are specified in [RFC8754]. Security
considerations for accepting link-layer ICMP messages and reflected
packets are discussed throughout the document.
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7. 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, 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, Greg Saccone,
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 acknowledged for their work on
the AERO implementation. Chuck Klabunde is honored and remembered
for his early leadership, 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
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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:
* The Internet Routing Overlay Network (IRON)
[RFC6179][I-D.templin-ironbis]
* Virtual Enterprise Traversal (VET)
[RFC5558][I-D.templin-intarea-vet]
* The Subnetwork Encapsulation and Adaptation Layer (SEAL)
[RFC5320][I-D.templin-intarea-seal]
* AERO, First Edition [RFC6706]
Note that these works cite numerous earlier efforts that are not also
cited here due to space limitations. The authors of those earlier
works are acknowledged for their insights.
This work is aligned with the NASA Safe Autonomous Systems Operation
(SASO) program under NASA contract number NNA16BD84C.
This work is aligned with the FAA as per the SE2025 contract number
DTFAWA-15-D-00030.
This work is aligned with the Boeing Commercial Airplanes (BCA)
Internet of Things (IoT) and autonomy programs.
This work is aligned with the Boeing Information Technology (BIT)
MobileNet program.
8. References
8.1. Normative References
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[I-D.templin-6man-omni]
Templin, F. L., "Transmission of IP Packets over Overlay
Multilink Network (OMNI) Interfaces", Work in Progress,
Internet-Draft, draft-templin-6man-omni-61, 25 April 2022,
<https://www.ietf.org/archive/id/draft-templin-6man-omni-
61.txt>.
[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>.
[RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander,
"SEcure Neighbor Discovery (SEND)", RFC 3971,
DOI 10.17487/RFC3971, March 2005,
<https://www.rfc-editor.org/info/rfc3971>.
[RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)",
RFC 3972, DOI 10.17487/RFC3972, March 2005,
<https://www.rfc-editor.org/info/rfc3972>.
[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>.
[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>.
[RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through
Network Address Translations (NATs)", RFC 4380,
DOI 10.17487/RFC4380, February 2006,
<https://www.rfc-editor.org/info/rfc4380>.
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[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>.
[RFC6081] Thaler, D., "Teredo Extensions", RFC 6081,
DOI 10.17487/RFC6081, January 2011,
<https://www.rfc-editor.org/info/rfc6081>.
[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>.
[RFC7739] Gont, F., "Security Implications of Predictable Fragment
Identification Values", RFC 7739, DOI 10.17487/RFC7739,
February 2016, <https://www.rfc-editor.org/info/rfc7739>.
[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>.
8.2. Informative References
[BGP] Huston, G., "BGP in 2015, http://potaroo.net", January
2016.
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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-
28, 18 May 2022, <https://www.ietf.org/archive/id/draft-
bonica-6man-comp-rtg-hdr-28.txt>.
[I-D.bonica-6man-crh-helper-opt]
Li, X., Bao, C., Ruan, E., and R. Bonica, "Compressed
Routing Header (CRH) Helper Option", Work in Progress,
Internet-Draft, draft-bonica-6man-crh-helper-opt-04, 11
October 2021, <https://www.ietf.org/archive/id/draft-
bonica-6man-crh-helper-opt-04.txt>.
[I-D.ietf-intarea-frag-fragile]
Bonica, R., Baker, F., Huston, G., Hinden, R. M., Troan,
O., and F. Gont, "IP Fragmentation Considered Fragile",
Work in Progress, Internet-Draft, draft-ietf-intarea-frag-
fragile-17, 30 September 2019,
<https://www.ietf.org/archive/id/draft-ietf-intarea-frag-
fragile-17.txt>.
[I-D.ietf-intarea-tunnels]
Touch, J. and M. Townsley, "IP Tunnels in the Internet
Architecture", Work in Progress, Internet-Draft, draft-
ietf-intarea-tunnels-10, 12 September 2019,
<https://www.ietf.org/archive/id/draft-ietf-intarea-
tunnels-10.txt>.
[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-29, 19 May 2022,
<https://www.ietf.org/archive/id/draft-ietf-ipwave-
vehicular-networking-29.txt>.
[I-D.ietf-rtgwg-atn-bgp]
Templin, F. L., 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-17, 19
April 2022, <https://www.ietf.org/archive/id/draft-ietf-
rtgwg-atn-bgp-17.txt>.
[I-D.templin-6man-dhcpv6-ndopt]
Templin, F. L., "A Unified Stateful/Stateless
Configuration Service for IPv6", Work in Progress,
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Internet-Draft, draft-templin-6man-dhcpv6-ndopt-11, 1
January 2021, <https://www.ietf.org/archive/id/draft-
templin-6man-dhcpv6-ndopt-11.txt>.
[I-D.templin-intarea-seal]
Templin, F. L., "The Subnetwork Encapsulation and
Adaptation Layer (SEAL)", Work in Progress, Internet-
Draft, draft-templin-intarea-seal-68, 3 January 2014,
<https://www.ietf.org/archive/id/draft-templin-intarea-
seal-68.txt>.
[I-D.templin-intarea-vet]
Templin, F. L., "Virtual Enterprise Traversal (VET)", Work
in Progress, Internet-Draft, draft-templin-intarea-vet-40,
3 May 2013, <https://www.ietf.org/archive/id/draft-
templin-intarea-vet-40.txt>.
[I-D.templin-ipwave-uam-its]
Templin, F. L., "Urban Air Mobility Implications for
Intelligent Transportation Systems", Work in Progress,
Internet-Draft, draft-templin-ipwave-uam-its-04, 4 January
2021, <https://www.ietf.org/archive/id/draft-templin-
ipwave-uam-its-04.txt>.
[I-D.templin-ironbis]
Templin, F. L., "The Interior Routing Overlay Network
(IRON)", Work in Progress, Internet-Draft, draft-templin-
ironbis-16, 28 March 2014,
<https://www.ietf.org/archive/id/draft-templin-ironbis-
16.txt>.
[I-D.templin-v6ops-pdhost]
Templin, F. L., "IPv6 Prefix Delegation and Multi-
Addressing Models", Work in Progress, Internet-Draft,
draft-templin-v6ops-pdhost-27, 1 January 2021,
<https://www.ietf.org/archive/id/draft-templin-v6ops-
pdhost-27.txt>.
[IEN48] Cerf, V., "The Catenet Model For Internetworking,
https://www.rfc-editor.org/ien/ien48.txt", July 1978.
[IEN48-2] Cerf, V., "The Catenet Model For Internetworking (with
figures), http://www.postel.org/ien/pdf/ien048.pdf", July
1978.
[OVPN] OpenVPN, O., "http://openvpn.net", October 2016.
Templin Expires 12 December 2022 [Page 100]
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[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>.
[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>.
[RFC2003] Perkins, C., "IP Encapsulation within IP", RFC 2003,
DOI 10.17487/RFC2003, October 1996,
<https://www.rfc-editor.org/info/rfc2003>.
[RFC2004] Perkins, C., "Minimal Encapsulation within IP", RFC 2004,
DOI 10.17487/RFC2004, October 1996,
<https://www.rfc-editor.org/info/rfc2004>.
[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>.
[RFC2983] Black, D., "Differentiated Services and Tunnels",
RFC 2983, DOI 10.17487/RFC2983, October 2000,
<https://www.rfc-editor.org/info/rfc2983>.
[RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
of Explicit Congestion Notification (ECN) to IP",
RFC 3168, DOI 10.17487/RFC3168, September 2001,
<https://www.rfc-editor.org/info/rfc3168>.
[RFC3330] IANA, "Special-Use IPv4 Addresses", RFC 3330,
DOI 10.17487/RFC3330, September 2002,
<https://www.rfc-editor.org/info/rfc3330>.
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[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>.
[RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally
Unique IDentifier (UUID) URN Namespace", RFC 4122,
DOI 10.17487/RFC4122, July 2005,
<https://www.rfc-editor.org/info/rfc4122>.
[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>.
[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271,
DOI 10.17487/RFC4271, January 2006,
<https://www.rfc-editor.org/info/rfc4271>.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, DOI 10.17487/RFC4291, February
2006, <https://www.rfc-editor.org/info/rfc4291>.
[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>.
[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>.
[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>.
[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>.
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[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>.
[RFC4982] Bagnulo, M. and J. Arkko, "Support for Multiple Hash
Algorithms in Cryptographically Generated Addresses
(CGAs)", RFC 4982, DOI 10.17487/RFC4982, July 2007,
<https://www.rfc-editor.org/info/rfc4982>.
[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>.
[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>.
[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>.
[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>.
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[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>.
[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>.
[RFC6273] Kukec, A., Krishnan, S., and S. Jiang, "The Secure
Neighbor Discovery (SEND) Hash Threat Analysis", RFC 6273,
DOI 10.17487/RFC6273, June 2011,
<https://www.rfc-editor.org/info/rfc6273>.
[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>.
[RFC6355] Narten, T. and J. Johnson, "Definition of the UUID-Based
DHCPv6 Unique Identifier (DUID-UUID)", RFC 6355,
DOI 10.17487/RFC6355, August 2011,
<https://www.rfc-editor.org/info/rfc6355>.
[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>.
[RFC6706] Templin, F., Ed., "Asymmetric Extended Route Optimization
(AERO)", RFC 6706, DOI 10.17487/RFC6706, August 2012,
<https://www.rfc-editor.org/info/rfc6706>.
[RFC6935] Eubanks, M., Chimento, P., and M. Westerlund, "IPv6 and
UDP Checksums for Tunneled Packets", RFC 6935,
DOI 10.17487/RFC6935, April 2013,
<https://www.rfc-editor.org/info/rfc6935>.
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[RFC6936] Fairhurst, G. and M. Westerlund, "Applicability Statement
for the Use of IPv6 UDP Datagrams with Zero Checksums",
RFC 6936, DOI 10.17487/RFC6936, April 2013,
<https://www.rfc-editor.org/info/rfc6936>.
[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>.
[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>.
[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>.
[WG] Wireguard, "WireGuard, https://www.wireguard.com", August
2020.
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Appendix A. Non-Normative Considerations
AERO can be applied to a multitude of Internetworking scenarios, with
each having its own adaptations. The following considerations are
provided as non-normative guidance:
A.1. Implementation Strategies for Route Optimization
Address resolution and route optimization as discussed in
Section 3.13 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 packets are still flowing.
However, the decision of when to initiate a new NS/NA(AR) exchange
and to perpetuate the process is left as an implementation detail.
One possible strategy may be to monitor the NCE watching for data
packets for (ReachableTime - 5) seconds. If any data packets have
been sent to the neighbor within this timeframe, then send an NS(AR)
to receive a new NA(AR). If no data packets 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 packets are sent within the 5 second window, reset
the NCE state to STALE.
The monitoring of the neighbor data packet traffic therefore becomes
an ongoing process during the NCE lifetime. If the NCE expires,
future data packets will trigger a new NS/NA(AR) exchange while the
packets themselves are delivered over a longer path 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
packets over a single interface at a time, and the neighbor always
observes packets arriving from the Client from the same link-layer
source address.
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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 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 packets
without any encapsulation. In that case, the Client sends packets
over the Direct link according to traffic selectors. If the Direct
interface is selected, then the Client's IP packets are transmitted
directly to the peer without going through an ANET/INET. If other
interfaces are selected, then the Client's IP packets are transmitted
via a different interface, which may result in the inclusion of
Proxy/Servers and Gateways in the communications path. Direct
interfaces must be tested periodically for reachability, e.g., via
NUD.
A.4. AERO Critical Infrastructure Considerations
AERO Gateways can be either Commercial off-the Shelf (COTS) standard
IP routers or virtual machines in the cloud. Gateways must be
provisioned, supported and managed by the INET administrative
authority, and connected to the Gateways of other INETs via inter-
domain peerings. Cost for purchasing, configuring and managing
Gateways is nominal even for very large OMNI links.
AERO INET Proxy/Servers can be standard dedicated server platforms,
but most often will be deployed as virtual machines in the cloud.
The only requirements for INET Proxy/Servers are that they can run
the AERO/OMNI code and have at least one network interface connection
to the INET. INET Proxy/Servers must be provisioned, supported and
managed by the INET administrative authority. Cost for purchasing,
configuring and managing cloud Proxy/Servers is nominal especially
for virtual machines.
AERO ANET Proxy/Servers are most often standard dedicated server
platforms with one underlay interface connected to the ANET and a
second interface connected to an INET. As with INET Proxy/Servers,
the only requirements are that they can run the AERO/OMNI code and
have at least one interface connection to the INET. ANET Proxy/
Servers must be provisioned, supported and managed by the ANET
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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.
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, ongoing 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 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.
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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:
* 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
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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.
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.
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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 RFC publication.
Author's Address
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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