Automatic Extended Route Optimization (AERO)
draft-templin-6man-aero-37
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 | 2021-11-19 (Latest revision 2021-11-15) | ||
| 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-37
Network Working Group F. Templin, Ed.
Internet-Draft Boeing Research & Technology
Intended status: Standards Track November 15, 2021
Expires: May 19, 2022
Automatic Extended Route Optimization (AERO)
draft-templin-6man-aero-37
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 link-local address format
that supports operation of the IPv6 Neighbor Discovery (IPv6 ND)
protocol. Prefix delegation/registration services are employed for
network admission and to manage the IP 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
services, 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
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on May 19, 2022.
Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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(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 Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Automatic Extended Route Optimization (AERO) . . . . . . . . 13
3.1. AERO Node Types . . . . . . . . . . . . . . . . . . . . . 14
3.2. The AERO Service over OMNI Links . . . . . . . . . . . . 15
3.2.1. AERO/OMNI Reference Model . . . . . . . . . . . . . . 15
3.2.2. Addressing and Node Identification . . . . . . . . . 18
3.2.3. AERO Routing System . . . . . . . . . . . . . . . . . 18
3.2.4. Segment Routing Topologies (SRTs) . . . . . . . . . . 20
3.2.5. Segment Routing For OMNI Link Selection . . . . . . . 21
3.3. OMNI Interface Characteristics . . . . . . . . . . . . . 21
3.4. OMNI Interface Initialization . . . . . . . . . . . . . . 23
3.4.1. AERO Proxy/Server and Relay Behavior . . . . . . . . 24
3.4.2. AERO Client Behavior . . . . . . . . . . . . . . . . 24
3.4.3. AERO Bridge Behavior . . . . . . . . . . . . . . . . 24
3.5. OMNI Interface Neighbor Cache Maintenance . . . . . . . . 25
3.5.1. OMNI ND Messages . . . . . . . . . . . . . . . . . . 27
3.5.2. OMNI Neighbor Advertisement Message Flags . . . . . . 28
3.5.3. OMNI Neighbor Window Synchronization . . . . . . . . 29
3.6. OMNI Interface Encapsulation and Fragmentation . . . . . 29
3.7. OMNI Interface Decapsulation . . . . . . . . . . . . . . 31
3.8. OMNI Interface Data Origin Authentication . . . . . . . . 32
3.9. OMNI Interface MTU . . . . . . . . . . . . . . . . . . . 32
3.10. OMNI Interface Forwarding Algorithm . . . . . . . . . . . 33
3.10.1. Client Forwarding Algorithm . . . . . . . . . . . . 34
3.10.2. Proxy/Server and Relay Forwarding Algorithm . . . . 35
3.10.3. Bridge Forwarding Algorithm . . . . . . . . . . . . 37
3.11. OMNI Interface Error Handling . . . . . . . . . . . . . . 38
3.12. AERO Mobility Service Coordination . . . . . . . . . . . 41
3.12.1. AERO Service Model . . . . . . . . . . . . . . . . . 41
3.12.2. AERO Client Behavior . . . . . . . . . . . . . . . . 42
3.12.3. AERO Proxy/Server Behavior . . . . . . . . . . . . . 43
3.13. AERO Route Optimization . . . . . . . . . . . . . . . . . 50
3.13.1. Multilink Address Resolution . . . . . . . . . . . . 50
3.13.2. Multilink Route Optimization . . . . . . . . . . . . 54
3.13.3. Rapid Commit Route Optimization . . . . . . . . . . 66
3.13.4. Client/Bridge Route Optimization . . . . . . . . . . 67
3.13.5. Client/Client Route Optimization . . . . . . . . . . 68
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3.14. Neighbor Unreachability Detection (NUD) . . . . . . . . . 70
3.15. Mobility Management and Quality of Service (QoS) . . . . 72
3.15.1. Mobility Update Messaging . . . . . . . . . . . . . 72
3.15.2. Announcing Link-Layer Information Changes . . . . . 73
3.15.3. Bringing New Links Into Service . . . . . . . . . . 74
3.15.4. Deactivating Existing Links . . . . . . . . . . . . 74
3.15.5. Moving Between Proxy/Servers . . . . . . . . . . . . 74
3.16. Multicast . . . . . . . . . . . . . . . . . . . . . . . . 75
3.16.1. Source-Specific Multicast (SSM) . . . . . . . . . . 76
3.16.2. Any-Source Multicast (ASM) . . . . . . . . . . . . . 77
3.16.3. Bi-Directional PIM (BIDIR-PIM) . . . . . . . . . . . 78
3.17. Operation over Multiple OMNI Links . . . . . . . . . . . 78
3.18. DNS Considerations . . . . . . . . . . . . . . . . . . . 79
3.19. Transition/Coexistence Considerations . . . . . . . . . . 79
3.20. Proxy/Server-Bridge Bidirectional Forwarding Detection . 80
3.21. Time-Varying MNPs . . . . . . . . . . . . . . . . . . . . 80
4. Implementation Status . . . . . . . . . . . . . . . . . . . . 80
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 81
6. Security Considerations . . . . . . . . . . . . . . . . . . . 81
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 83
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 85
8.1. Normative References . . . . . . . . . . . . . . . . . . 85
8.2. Informative References . . . . . . . . . . . . . . . . . 87
Appendix A. Non-Normative Considerations . . . . . . . . . . . . 93
A.1. Implementation Strategies for Route Optimization . . . . 93
A.2. Implicit Mobility Management . . . . . . . . . . . . . . 94
A.3. Direct Underlying Interfaces . . . . . . . . . . . . . . 94
A.4. AERO Critical Infrastructure Considerations . . . . . . . 95
A.5. AERO Server Failure Implications . . . . . . . . . . . . 95
A.6. AERO Client / Server Architecture . . . . . . . . . . . . 96
Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 98
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 98
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
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 one or more underlying
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
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improved performance and Maximum Transmission Unit (MTU) diversity.
In terms of precedence, this specification may provide first-
principle insights into a representative mobility service
architecture as context for understanding the OMNI specification.
The AERO service connects Clients over Proxy/Servers and Relays that
are seen as OMNI link neighbors, and includes Bridges that
interconnect diverse Internetworks as OMNI link segments through OAL
forwarding at a layer below IP. Each node's OMNI interface uses an
IPv6 link-local address format that supports operation of the IPv6
Neighbor Discovery (IPv6 ND) protocol [RFC4861]. A node's OMNI
interface can be configured over multiple underlying 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 and without changing their IP Address.
AERO Bridges peer with Proxy/Servers in a secured private BGP overlay
routing instance to establish a Segment Routing Topology (SRT)
spanning tree over the underlying Internetworks of one or more
disjoint administrative domains 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 the underlying
Internetwork to (mobile or fixed) nodes on the OMNI link. To the
underlying Internetwork, the Relay is the source of a route to the
MSP; hence uplink traffic to mobile nodes is naturally routed to the
nearest Relay.
AERO can be used with OMNI links that span private-use Internetworks
and/or public Internetworks such as the global 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 is therefore provided.
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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 underlying 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, etc.
3. Mobility - a mobile node's ability to change network points of
attachment (e.g., moving between wireless base stations) which
may result in an underlying 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
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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] while including the OMNI
option 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.
Access Network (ANET)
a node's first-hop data link service network (e.g., a radio access
network, cellular service provider network, corporate enterprise
network, etc.) that often provides link-layer security services
such as IEEE 802.1X and physical-layer security (e.g., "protected
spectrum") to prevent unauthorized access internally and with
border network-layer security services such as firewalls and
proxys that prevent unauthorized outside access.
ANET interface
a node's attachment to a link in an ANET.
Internetwork (INET)
a network topology with a coherent IP routing and addressing plan
and that provides a transit backbone service for its connected end
systems. INETs also provide an underlay service over which the
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AERO virtual link is configured. Example INETs include corporate
enterprise networks, aviation networks, and the public Internet
itself. When there is no administrative boundary between an ANET
and the INET, the ANET and INET are one and the same.
INET interface
a node's attachment to a link in an INET.
*NET
a "wildcard" term referring to either ANET or INET when it is not
necessary to draw a distinction between the two.
*NET interface
a node's attachment to a link in a *NET.
*NET Partition
frequently, *NETs 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 *NET partition is seen as a separate OMNI link segment as
discussed throughout this document.)
*NET encapsulation
the encapsulation of a packet in an outer header or headers that
can be routed within the scope of the local *NET partition.
*NET address
the IP address (and also UDP port number when UDP is used) that
appears in *NET encapsulations sent over a node's interface
connection to a *NET.
INADDR
the same as defined for "*NET" address above, with both terms used
interchangeably throughout the document.
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 underlying *NET 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 underlying *NET 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.
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OMNI Interface
a node's attachment to an OMNI link. Since OMNI interface
addresses are managed for uniqueness, OMNI interfaces do not
require Duplicate Address Detection (DAD) and therefore set the
administrative variable 'DupAddrDetectTransmits' to zero
[RFC4862].
OMNI Adaptation Layer (OAL)
an OMNI interface service that subjects original IP packets
admitted into the interface to mid-layer IPv6 header encapsulation
followed by 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 a bridged OMNI link.
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
*NET encapsulation, or following *NET 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 *NET encapsulation or prior
to *NET decapsulation. OAL sources and destinations exchange
carrier packets over underlying interfaces, and may be separated
by one or more OAL intermediate nodes. OAL intermediate nodes re-
encapsulate carrier packets during forwarding by removing the *NET
headers of the previous hop underlying network and replacing them
with new *NET headers for the next hop underlying 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 *NET encapsulation to create carrier packets.
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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.
OAL intermediate node
an OMNI interface acts as an OAL intermediate node when it removes
the *NET headers of carrier packets received from a previous hop,
then re-encapsulates the carrier packets in new *NET 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.
underlying interface
a *NET interface over which an OMNI interface is configured.
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.
Mobile Network Prefix Link Local Address (MNP-LLA)
an IPv6 Link Local Address that embeds the most significant 64
bits of an MNP in the lower 64 bits of fe80::/64, as specified in
[I-D.templin-6man-omni].
Mobile Network Prefix Unique Local Address (MNP-ULA)
an IPv6 Unique-Local Address derived from an MNP-LLA.
Administrative Link Local Address (ADM-LLA)
an IPv6 Link Local Address that embeds a 32-bit administratively-
assigned identification value in the lower 32 bits of fe80::/96,
as specified in [I-D.templin-6man-omni].
Administrative Unique Local Address (ADM-ULA)
an IPv6 Unique-Local Address derived from an ADM-LLA.
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AERO node
a node that is connected to an OMNI link and participates in the
AERO internetworking and mobility service.
AERO Client ("Client")
an AERO node that connects over one or more underlying interfaces
and requests MNP delegation/registration service from AERO Proxy/
Servers. The Client assigns an MNP-LLA 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.
AERO Proxy/Server ("Proxy/Server")
a node that provides a proxying service between AERO Clients and
external peers on its Client-facing ANET interfaces (i.e., in the
same fashion as for an enterprise network proxy) as well as
designated router services for coordination with correspondents on
its INET-facing interfaces. (Proxy/Servers in the open INET
instead configure only a single INET interface and no ANET
interfaces.) The Proxy/Server configures an OMNI interface and
assigns an ADM-LLA 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 Bridges.
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 configure an OMNI interface, assign an ADM-
LLA and maintain BGP peerings with Bridges the same as Proxy/
Servers and run a dynamic routing protocol to discover any non-MNP
IP GUA routes in service on other links/networks. The Relay
advertises the MSP(s) to its other links/networks, and
redistributes routes discovered on other links/networks into the
OMNI link BGP routing system the same as for Proxy/Servers.
(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 Bridge ("Bridge")
a BGP hub autonomous system node that also provides OAL forwarding
services for nodes on an OMNI link. Bridges forwards 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. Bridges peer
with Proxy/Servers and other Bridges to form a spanning tree over
all OMNI link segments and to discover the set of all MNP and non-
MNP prefixes in service. Bridges process carrier packets received
over the secured spanning tree that are addressed to themselves,
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while forwarding all other carrier packets to the next hop also
via the secured spanning tree. Bridges 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) Proxy/Server
a Proxy/Server for a source Client's underlying 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.
Hub Proxy/Server
a single Proxy/Server selected by a Client that provides a
designated router service for all of the Client's underlying
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 in that capacity), 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).
Last-Hop Segment (LHS) Proxy/Server
a Proxy/Server for an underlying interface of the target Client
that forwards packets received from the segment routing topology
to the target Client over that interface.
Segment Routing Topology (SRT)
a multinet OMNI link forwarding region between FHS and LHS Proxy/
Servers. FHS/LHS Proxy/Servers and SRT Bridges span the OMNI link
on behalf of source/target Client pairs. The SRT maintains a
spanning tree established through BGP peerings between Bridges and
Proxy/Servers. Each SRT segment includes Bridges in a "hub" and
Proxy/Servers in "spokes", while adjacent segments are
interconnected by Bridge-Bridge peerings. The BGP peerings are
configured over both secured and unsecured underlying network
paths such that a secured spanning tree is available for critical
control messages while other messages can use the unsecured
spanning tree.
link-layer address
an IP address used as an encapsulation header source or
destination address from the perspective of the OMNI interface.
When an upper layer protocol (e.g., UDP) is used as part of the
encapsulation, the port number is also considered as part of the
link-layer address.
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network layer address
the source or destination address of an original IP packet
presented to the OMNI interface.
end user network (EUN)
an internal virtual or external edge IP network that an AERO
Client or Relay connects to the rest of the network via the OMNI
interface. The Client/Relay sees each EUN as a "downstream"
network, and sees the OMNI interface as the point of attachment to
the "upstream" network.
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.
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.
Route Optimization Source (ROS)
the AERO node nearest the source that initiates route
optimization. The ROS may be a FHS Proxy/Server or Relay for the
source, or may be the source Client itself.
Route Optimization responder (ROR)
the AERO node that responds to route optimization requests on
behalf of the target. The ROR may be either the target MNP Client
itself, the Client's current Hub Proxy/Server or a Relay for a
non-MNP target.
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 Bridges that tracks all Proxy/Server-to-Client associations.
Mobility Service (MS)
the collective set of all Proxy/Servers, Bridges and Relays that
provide the AERO Service to Clients.
Multilink Forwarding Information Base (MFIB)
A forwarding table on each AERO/OMNI source, destination and
intermediate node that includes Multilink Forwarding Vectors (MFV)
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with both next hop forwarding instructions and context for
reconstructing compressed headers for specific underlying
interface pairs used to communicate with peers.
Multilink Forwarding Vector (MFV)
An MFIB entry that includes soft state for each underlying
interface pairwise communication session between peer OMNI nodes.
MFVs are identified by both a next-hop and previous-hop MFV Index
(MFVI), with the next-hop established based on an IPv6 ND
solicitation and the previous hop established based on the
solicited IPv6 ND advertisement response.
Multilink Forwarding Vector Index (MVFI)
A 4 octet value selected by an AERO/OMNI node when it creates an
MFV, then advertises to either a next-hop or previous-hop. AERO/
OMNI intermediate nodes assign two distinct local MFVIs for each
MFV and advertise one to the next-hop and the other to the
previous-hop. AERO/OMNI end systems assign and advertise a single
MFVI. AERO/OMNI nodes also discover the remote MFVIs advertised
by other nodes that indicate a value the remote node is willing to
accept.
Throughout the document, the simple terms "Client", "Proxy/Server",
"Bridge" and "Relay" refer to "AERO Client", "AERO Proxy/Server",
"AERO Bridge" 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] and DHCPv6 [RFC8415] (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.
3. Automatic Extended Route Optimization (AERO)
The following sections specify the operation of IP over OMNI links
using the AERO service:
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3.1. AERO Node Types
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 underlying 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 nodes on
EUNs. AERO Bridges, 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.
AERO Bridges (together with Proxy/Servers) provide the secured
backbone supporting infrastructure for a Segment Routing Topology
(SRT) spanning tree for the OMNI link. Bridges 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 Bridge also peers with Proxy/
Servers and other Bridges 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). Bridges assign one or more
Mobility Service Prefixes (MSPs) to the OMNI link and configure
secured tunnels with Proxy/Servers, Relays and other Bridges; they
further maintain forwarding table entries for each MNP or non-MNP
prefix in service on the OMNI link.
AERO Proxy/Servers distributed across one or more SRT segments
provide default forwarding and mobility/multilink services for AERO
Client mobile nodes. Each Proxy/Server also peers with Bridges 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 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 Bridge. 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.
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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 Bridge 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:
+----------------+
| AERO Bridge B1 |
| Nbr: S1, S2, P1|
|(X1->S1; X2->S2)|
| MSP M1 |
+-------+--------+
+--------------+ | +--------------+
| AERO P/S S1 | | | AERO P/S S2 |
| Nbr: C1, B1 | | | Nbr: C2, B1 |
| default->B1 | | | default->B1 |
| X1->C1 | | | X2->C2 |
+-------+------+ | +------+-------+
| OMNI link | |
X===+===+==================+===================+===+===X
| |
+-----+--------+ +--------+-----+
|AERO Client C1| |AERO Client C2|
| Nbr: S1 | | Nbr: S2 |
| default->S1 | | default->S2 |
| MNP X1 | | MNP X2 |
+------+-------+ +-----+--------+
| |
.-. .-.
,-( _)-. ,-( _)-.
.-(_ IP )-. +-------+ +-------+ .-(_ IP )-.
(__ EUN )--|Host H1| |Host H2|--(__ EUN )
`-(______)-' +-------+ +-------+ `-(______)-'
Figure 1: AERO/OMNI Reference Model
In this model:
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o the OMNI link is an overlay network service configured over one or
more underlying SRT segments which may be managed by different
administrative authorities and have incompatible protocols and/or
addressing plans.
o AERO Bridge B1 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).
Bridges provide the backbone for an SRT spanning tree for the OMNI
link.
o AERO Proxy/Servers S1 and S2 configure secured tunnels with Bridge
B1 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.)
o AERO Clients C1 and C2 associate with Proxy/Servers S1 and S2,
respectively. They receive MNP delegations X1 and X2, and also
act as default routers for their associated physical or internal
virtual EUNs. Simple hosts H1 and H2 attach to the EUNs served by
Clients C1 and C2, respectively.
An OMNI link configured over a single *NET appears as a single
unified link with a consistent underlying network addressing plan;
all nodes on the link can exchange carrier packets via simple *NET
encapsulation (i.e., following any necessary NAT traversal) since the
underlying *NET is connected. In common practice, however, OMNI
links are often configured over an SRT spanning tree that bridges
multiple distinct *NET segments managed under different
administrative authorities (e.g., as for worldwide aviation service
providers such as ARINC, SITA, Inmarsat, etc.). Individual *NETs 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
Bridges.
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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:
. . . . . . . . . . . . . . . . . . . . . . .
. .
. .-(::::::::) .
. .-(::::::::::::)-. +-+ .
. (:::: Segment A :::)--|B|---+ .
. `-(::::::::::::)-' +-+ | .
. `-(::::::)-' | .
. | .
. .-(::::::::) | .
. .-(::::::::::::)-. +-+ | .
. (:::: Segment B :::)--|B|---+ .
. `-(::::::::::::)-' +-+ | .
. `-(::::::)-' | .
. | .
. .-(::::::::) | .
. .-(::::::::::::)-. +-+ | .
. (:::: Segment C :::)--|B|---+ .
. `-(::::::::::::)-' +-+ | .
. `-(::::::)-' | .
. | .
. ..(etc).. x .
. .
. .
. <- Segment Routing Topology (SRT) -> .
. (Spanned by OMNI Link) .
. . . . . . . . . . . . . .. . . . . . . . .
Figure 2: OMNI Link Segment Routing Topology (SRT)
Bridge, Proxy/Server and Relay OMNI interfaces are configured over
both secured tunnels and open INET underlying interfaces within their
respective SRT segments. Within each segment, Bridges configure
"hub-and-spokes" BGP peerings with Proxy/Server/Relays as "spokes".
Adjacent SRT segments are joined by Bridge-to-Bridge 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
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carrier packets to take more direct paths between OMNI link neighbors
without having to follow strict spanning tree paths.
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 used for network-layer addresses
in link-scoped IPv6 ND and data messages. AERO Clients use LLAs
constructed from MNPs (i.e., "MNP-LLAs") while other AERO nodes use
LLAs constructed based on 32-bit Mobility Service ID (MSID) values
("ADM-LLAs") per [I-D.templin-6man-omni]. Non-MNP routes are also
represented the same as for MNP-LLAs, 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 OMNI domain identifier to form the
prefix [ULA]::/48, then include a 16-bit OMNI link identifier '*' to
form the prefix [ULA*]::/64 [RFC4291]. The AERO node then uses the
prefix [ULA*]::/64 to form "MNP-ULAs" or "ADM-ULA"s as specified in
[I-D.templin-6man-omni] to support OAL addressing. (The prefix
[ULA*]::/64 appearing alone and with no suffix represents "default".)
AERO Clients also use Temporary ULAs constructed per
[I-D.templin-6man-omni], where the addresses are typically used only
in initial control message exchanges until a stable MNP-LLA/ULA is
assigned.
AERO MSPs, MNPs and non-MNP routes are typically based on Global
Unicast Addresses (GUAs), but in some cases may be based on private-
use addresses. A GUA block is also reserved for OMNI link anycast
purposes. See [I-D.templin-6man-omni] for a full specification of
LLAs, ULAs and GUAs 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 Bridges and 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 discovered 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
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with one or more Bridges but does not peer with other Proxy/Servers.
Each SRT segment in the OMNI link must include one or more Bridges in
a "hub" AS, which peer with the Proxy/Servers within that segment as
"spoke" ASes. All Bridges 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 Bridges of different segments peer
with one another using eBGP.
Bridges maintain forwarding table entries only for the MNP-ULAs
corresponding to MNP and non-MNP routes that are currently active,
and also maintain black-hole routes for the OMNI link MSPs so that
carrier packets destined to non-existent MNP-ULAs are dropped with a
Destination Unreachable message returned. In this way, Proxy/Servers
and Relays have only partial topology knowledge (i.e., they only
maintain routing information for their directly associated Clients
and non-AERO links) and they forward all other carrier packets to
Bridges which have full topology knowledge.
Each OMNI link segment assigns a unique ADM-ULA sub-prefix of
[ULA*]::/96 known as the "SRT prefix". For example, a first segment
could assign [ULA*]::1000/116, a second could assign
[ULA*]::2000/116, a third could assign [ULA*]::3000/116, etc. Within
each segment, each Proxy/Server configures an ADM-ULA within the
segment's SRT prefix, e.g., the Proxy/Servers within [ULA*]::2000/116
could assign the ADM-ULAs [ULA*]::2011/116, [ULA*]::2026/116,
[ULA*]::2003/116, etc.
The administrative authorities for each segment must therefore
coordinate to assure mutually-exclusive ADM-ULA prefix assignments,
but internal provisioning of ADM-ULAs an independent local
consideration for each administrative authority. For each ADM-ULA
prefix, the Bridge(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*]::1023/116 is
simply [ULA*]::1000.
ADM-ULA prefixes are statically represented in Bridge forwarding
tables. Bridges 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 ADM-ULA prefixes either via standard BGP routing or
static routes. For example, if three Bridges ('A', 'B' and 'C') from
different segments serviced [ULA*]::1000/116, [ULA*]::2000/116 and
[ULA*]::3000/116 respectively, then the forwarding tables in each
Bridge appear as follows:
A: [ULA*]::1000/116->local, [ULA*]::2000/116->B, [ULA*]::3000/116->C
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B: [ULA*]::1000/116->A, [ULA*]::2000/116->local, [ULA*]::3000/116->C
C: [ULA*]::1000/116->A, [ULA*]::2000/116->B, [ULA*]::3000/116->local
These forwarding table entries rarely change, since they correspond
to fixed infrastructure elements in their respective segments.
MNP (and non-MNP) ULAs are instead dynamically advertised in the AERO
routing system by Proxy/Servers and Relays that provide service for
their corresponding MNPs. 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: [ULA*]:2001:db8:1000:2000/120
E: [ULA*]:2001:db8:3000:4000/120
F: [ULA*]: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 64-bit sub-prefixes of [ULA]::/48 identify up to 2^16 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 bits 48-63 of
[ULA]::/48, i.e., as [ULA0]::/64, [ULA1]::/64, [ULA2]::/64, etc.
Each OMNI interface is identified by a unique interface name (e.g.,
omni0, omni1, omni2, etc.) 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 Bridges and Proxy/Servers of each independent SRT engage in BGP
peerings to form a spanning tree with the Bridges in non-leaf nodes
and the Proxy/Servers in leaf nodes. The spanning tree is configured
over both secured and unsecured underlying network paths. The
secured spanning tree is used to convey secured control messages
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between Proxy/Servers and Bridges, while the unsecured spanning tree
forwards data messages and/or unsecured control messages.
Each SRT segment is identified by a unique ADM-ULA prefix used by all
Proxy/Servers and Bridges 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.
3.2.5. Segment Routing For OMNI Link Selection
Original IPv6 source 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
underlying interfaces classified as follows:
o INET interfaces connect to an INET either natively or through one
or more NATs. Native INET interfaces have global IP addresses
that are reachable from any INET correspondent. The INET-facing
interfaces of Proxy/Servers are native interfaces, as are Relay
and Bridge interfaces. NATed INET interfaces connect to a private
network behind one or more NATs with the outermost NAT providing
INET access. Clients that are behind a NAT are required to send
periodic keepalive messages to keep NAT state alive when there are
no carrier packets flowing.
o ANET interfaces connect to an ANET that is separated from the open
INET by an FHS Proxy/Server. Clients can issue control messages
over the ANET without including an authentication signature since
the ANET is secured at the network layer or below. Proxy/Servers
can actively issue control messages over the INET on behalf of
ANET Clients to reduce ANET congestion. The same as for INET
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interfaces, there may be NATs on the path from the Client to its
FHS Proxy/Server.
o VPNed interfaces use security encapsulation over the INET to a
Virtual Private Network (VPN) server that also acts as an FHS
Proxy/Server. Other than the link-layer encapsulation format,
VPNed interfaces behave the same as Direct interfaces.
o Direct (i.e., single-hop point-to-point) interfaces connect a
Client directly to an FHS Proxy/Server without crossing any ANET/
INET paths. An example is a line-of-sight link between a remote
pilot and an unmanned aircraft. The same Client considerations
apply as for VPNed interfaces.
OMNI interfaces use OAL encapsulation and fragmentation as discussed
in Section 3.6. OMNI interfaces use *NET 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 do not use link-layer encapsulation over Direct
underlying interfaces or ANET interfaces when the Client and FHS
Proxy/Server are known to be on the same underlying 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) and Neighbor Advertisement (NA) 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 containing link information
parameters for the OMNI interface's underlying interfaces and any
other per-neighbor information.
A Client's OMNI interface may be configured over multiple underlying
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.
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If a Client's multiple underlying 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
Multilink Forwarding Parameters sub-options with the same underlying
interface index. In that case, the Client would appear to have a
single underlying interface but with a dynamically changing link-
layer address.
If the Client has multiple active underlying 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 Multilink Forwarding Parameters
sub-options with different underlying interface indexes.
Proxy/Servers on the open Internet include only a single INET
underlying 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
underlying interface. ANET Clients therefore must discover both the
ANET and INET INADDR information for the Proxy/Server.
Bridge and Proxy/Server OMNI interfaces are configured over
underlying 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 both
an ADM-LLA and its corresponding ADM-ULA, and acts as an OAL source
to encapsulate and fragment original IP packets while presenting the
resulting carrier packets over the secured or unsecured underlying
paths. Note that Bridge and Proxy/Server end-to-end transport
protocol sessions used by the BGP are run directly over the OMNI
interface and use ADM-ULA 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 ADM-ULAs as the original IP header) and forwards
them over the secured underlying path.
3.4. OMNI Interface Initialization
AERO Proxy/Servers and Clients configure OMNI interfaces as their
point of attachment to the OMNI link. AERO nodes assign the MSPs for
the link to their OMNI interfaces (i.e., as a "route-to-interface")
to ensure that original IP packets with destination addresses covered
by an MNP not explicitly associated with another interface are
directed to an OMNI interface.
OMNI interface initialization procedures for Proxy/Servers, Clients
and Bridges are discussed in the following sections.
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3.4.1. AERO Proxy/Server and Relay Behavior
When a Proxy/Server enables an OMNI interface, it assigns an
ADM-{LLA,ULA} appropriate for the given OMNI link SRT segment. The
Proxy/Server also configures secured tunnels with one or more
neighboring Bridges and engages in BGP routing protocol sessions with
one or more Bridges.
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 underlying 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/EUN
interfaces (see: Section 3.2.3). The Relay provisions MNPs to
networks on the INET/EUN interfaces (i.e., the same as a Client would
do) and advertises the MSP(s) for the OMNI link over the INET/EUN
interfaces. The Relay further provides an attachment point of the
OMNI link to a non-MNP-based global topology.
3.4.2. AERO Client Behavior
When a Client enables an OMNI interface, it assigns either an
MNP-{LLA, ULA} or a Temporary ULA and sends RS messages over its
underlying 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 Temporary ULA in its initial RS message, it will
discover an MNP-{LLA,ULA} in the corresponding RA that it receives
from the FHS Proxy/Server 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 Temporary ULAs for Client-to-Client communications until it
encounters an infrastructure element that can delegate an MNP.)
3.4.3. AERO Bridge Behavior
AERO Bridges configure an OMNI interface and assign an ADM-ULA and
corresponding Subnet Router Anycast address for each OMNI link SRT
segment they connect to. Bridges configure secured tunnels with
Proxy/Servers in the same SRT segment and other Bridges in the same
(or an adjacent) SRT segment. Bridges then engage in a BGP routing
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protocol session with neighbors over the secured spanning tree (see:
Section 3.2.3).
3.5. OMNI Interface Neighbor Cache Maintenance
Each 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
LLA of the neighbor, while the OAL encapsulation ULA 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.
Bridges also maintain NCEs for Clients within their local segments
based on NS/NA route optimization messaging (see: Section 3.13.4).
When a Bridge creates/updates a NCE for a local segment Client based
on NS/NA route optimization, it also maintains MVFI 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.
Clients determine the service profiles for their FHS and Hub Proxy/
Servers by setting the N/A/U flags in 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 option extension header 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
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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 underlying Interface Attributes, while FHS Proxy/
Servers acting in "proxy" mode have knowledge of only the individual
Client underlying 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.
Clients act as RORs on their own behalf when they receive an NS(AR)
from an ROS via their Hub Proxy/Server (Relays instead act as RORs on
behalf of non-MNP targets specific to other links/networks that the
Relay services and/or "default"). The ROR returns and NA(AR)
response to the ROS, which creates or updates a NCE for the target
network-layer and link-layer addresses. The ROS then (re)sets
ReachableTime for the NCE to REACHABLE_TIME seconds and performs
reachability tests over specific underlying interface pairs to
determine paths for forwarding carrier packets directly to the
target. The ROS 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].
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.
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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]. 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 underlying 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.
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 underlying 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 an ADM-LLA while using unicast link-layer
addresses. AERO Proxy/Servers respond by returning unicast RA
messages. During the RS/RA exchange, AERO Clients and Proxy/Servers
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include state synchronization parameters to establish Identification
windows and other state.
AERO nodes use NS/NA messages for the following purposes:
o NS/NA(AR) messages are used for address resolution and optionally
to establish sequence number windows. The ROS sends an NS(AR) to
the solicited-node multicast address of the target, and an ROR
with addressing information for the target returns a unicast
NA(AR) that contains current, consistent and authentic target
address resolution information. NS/NA(AR) messages must be
secured.
o NS/NA(NUD) messages are used to establish multilink forwarding
state and determine target reachability. The source sends an
NS(NUD) to the unicast address of the target while naming a
specific underlying interface pair, and the target returns a
unicast NA(NUD). 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) messages may also be used to
establish window synchronization and/or MFIB state, in which case
the messages must be secured.
o 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.
o NS/NA(DAD) messages are not used in AERO, since Duplicate Address
Detection is not required.
Additionally, nodes may sent 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:
o 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.
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o 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 O: The O ("Override") flag is set to 0 for solicited NAs returned
by a Proxy/Server ROR 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 MNP-LLAs must be
uniquely assigned to Clients to support correct IPv6 ND protocol
operation, however, no role is currently seen for assigning the
same MNP-LLA 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 in NS/NA message exchanges to maintain
send/receive window state in their respective neighbor cache entries
as specified 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. This 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 if necessary containing one or more Multilink
Forwarding Vector Indices (MFVIs) as discussed in Section 3.13. (The
OAL source can then optionally invoke OAL header compression by
replacing the OAL IPv6 header, CRH-32 and Fragment Header with an OAL
Compressed Header (OCH), Type 0 or 1.)
The OAL source finally encapsulates each resulting OAL fragment in
*NET headers to form an OAL carrier packet, with source address set
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to its own *NET address (e.g., 192.0.2.100) and destination set to
the *NET 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:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| *NET Header |
| src = 192.0.2.100 |
| dst = 192.0.2.1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OAL IPv6 Header |
| src = [ULA*]::2001:db8:1:2 |
| dst= [ULA*]::3000:0000 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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
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 *NET
header is 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 MNP-ULA prefix
information that may change dynamically due to regional node mobility
as well as Relay non-MNP-ULA and per-segment ADM-ULA prefix
information that rarely changes. OMNI link Bridges and Proxy/Servers
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use the information to establish and 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 *NET encapsulation headers
from the first segment and re-encapsulates the packet in new *NET
encapsulation headers for the next segment.
When an FHS Bridge receives a carrier packet with an OCH-0/1 header
that must be forwarded to an LHS Bridge 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 Bridge
includes a single MFVI in the CRH-32 that will be meaningful to the
LHS Bridge. When the LHS Bridge 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:
o AERO Bridges and Proxy/Servers accept carrier packets received
from the secured spanning tree.
o AERO Proxy/Servers and Clients accept carrier packets and original
IP packets that originate from within the same secured ANET.
o AERO Clients and Relays accept original IP packets from downstream
network correspondents based on ingress filtering.
o AERO Clients, Relays, Proxy/Servers and Bridges verify carrier
packet UDP/IP encapsulation addresses according to
[I-D.templin-6man-omni].
o 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 underlying links with diverse MTUs while
observing both a minimum and per-path Maximum Payload Size (MPS).
The functions of the OAL and the OMNI interface MTU/MRU/MPS are
specified in [I-D.templin-6man-omni].
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 together into a
single OAL super-packet as discussed in [I-D.templin-6man-omni]
before applying fragmentation. The OAL source then encapsulates each
OAL fragment in *NET headers for transmission as carrier packets over
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an underlying interface connected to either a physical link (such as
Ethernet, WiFi and the like) 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 Bridge in the
path (see: Section 3.10.3), 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 underlying 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 underlying interfaces and/or
neighbor cache entries for neighbors with multiple underlying
interfaces (see Section 3.3). The OAL uses Interface Attributes and/
or Traffic Selectors (e.g., port number, flow specification, etc.) to
select an outbound underlying interface for each OAL packet and also
to select segment routing and/or link-layer destination addresses
based on the neighbor's underlying interfaces. AERO implementations
SHOULD permit network management to dynamically adjust Traffic
Selector values at runtime.
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
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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 underlying
interface pair to avoid complicating factors such as delay variance
and reordering.) AERO nodes keep track of which underlying
interfaces are currently "reachable" or "unreachable", and only use
"reachable" interfaces for forwarding purposes.
The following sections discuss the OMNI interface forwarding
algorithms for Clients, Proxy/Servers and Bridges. 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 an MNP-LLA).
3.10.1. 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, the Client selects one or
more "reachable" neighbor interfaces in the entry for forwarding
purposes. Otherwise, the Client invokes route optimization per
Section 3.13 and follows the multilink forwarding procedures outlined
there.
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 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).
Note: Clients and their FHS Proxy/Server (and other Client) peers can
exchange original IP packets over ANET underlying 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
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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.)
3.10.2. 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 ADM-
ULA. When the Proxy/Server receives carrier packets on underlying
interfaces with OAL destination set to its own ADM-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 ROS to initiate route
optimization as specified in Section 3.13.
When the Proxy/Server receives a carrier packet with OAL destination
set to an MNP-ULA 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
MNP-ULA. 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 the MNP-ULA 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
ADM-ULA of the new Proxy/Server, then re-encapsulates the carrier
packet and forwards it to a Bridge which will eventually deliver it
to the new Proxy/Server. If the neighbor cache state for the MNP-ULA
is REACHABLE, the Proxy/Server forwards the carrier packets to the
Client which then must reassemble. (Note that the Proxy/Server does
not reassemble carrier packets not explicitly addressed to its own
ADM-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 that are smaller than its link
MTU but that can still be reassembled.
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Proxy/Servers process carrier packets with OAL destinations that do
not match their ADM-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 the MNP-ULA of one of their Clients received over the
secured spanning tree.) Proxy/Servers process carrier packets with
their ADM-ULA as the destination by first examining the packet for a
CRH-32 header or an OCH-0/1 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 *NET 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 ADM-ULA with CRH-32s that include additional forwarding
information. Proxy/Servers use the forwarding information to
determine the correct NCE and underlying 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.
Note: Clients and their FHS Proxy/Server peers can exchange original
IP packets over ANET underlying 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 ADM-ULA from any Client, the Proxy/Server reassembles if
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necessary then performs ROS 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 ROS on its own behalf and
thereby "override" the Proxy/Server's ROS 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.
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].
3.10.3. Bridge Forwarding Algorithm
Bridges forward spanning tree carrier packets while decrementing the
OAL header Hop Count but not the original IP header Hop Count/TTL.
Bridges 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 Bridge receives a carrier packet, it
removes the outer *NET header and searches for an MFIB entry that
matches an MFVI or an IP forwarding table entry that matches the OAL
destination address.
Bridges process carrier packets with OAL destinations that do not
match their ADM-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
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to themselves. Bridges process carrier packets with their ADM-ULA or
the SRT Subnet Router Anycast address as the destination by first
examining the packet for a full OAL header with a CRH-32 extension or
an OCH-0/1 header. In that case, the Bridge 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
Bridge 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. If the Bridge has a NCE
for the target Client with an entry for the target underlying
interface and current *NET addresses, the Bridge instead forwards
directly to the target Client while using the final hop MFVI instead
of the next hop (see: Section 3.13.4).
Bridges forward carrier packets received from a first segment via the
secured spanning tree to the next segment also via the secured
spanning tree. Bridges forward carrier packets received from a first
segment via the unsecured spanning tree to the next segment also via
the unsecured spanning tree. Bridges 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 underlying interface to be used for transmission
(i.e., a secured tunnel or an open INET interface).
As for Proxy/Servers, Bridges must verify that the *NET 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 the *NET 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
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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:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
| IP Header of link layer |
| error message |
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ICMP Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ---
~ ~ P
| carrier packet *NET 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:
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o 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].
o 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.
o 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.
o 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.
o 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 underlying path as unusable and use another
underlying path.
o 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 Bridge receives a carrier packet for which the network-
layer destination address is covered by an MSP assigned to a black-
hole route, the Bridge 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.
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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 the 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.
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 underlying interfaces with a FHS
Proxy/Server. Each FHS Proxy/Server locally services one or more of
the Client's underlying 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 underlying 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 ADM-LLA 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 ADM-
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LLA 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 ADM-LLA of another Proxy/Server to serve as a Hub.)
AERO 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 MNP-LLA 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 the unspecified address (::) 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 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 Client Behavior
AERO 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 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 Client can
resolve the DNS Fully-Qualified Domain Name (FQDN)
"linkupnetworks.[domainname]" where "linkupnetworks" is a constant
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text string and "[domainname]" is a DNS suffix for the OMNI link
(e.g., "example.com").
The Client then performs RS/RA exchanges over each of its underlying
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 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 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 Client registers its underlying 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 Client prepares an RS message to send over any available
underlying 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 underlying interface.
When the 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 Client wishes to discontinue use of a Hub Proxy/Server it
issues an RS message over any underlying interface with an OMNI
option with a prefix release indication (i.e., by setting the OMNI
extension header Preflen to 0). When the Hub Proxy/Server processes
the message, it releases the MNP, sets the NCE state for the 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 Client
associates with a new FHS/Hub Proxy/Server it can include an OMNI
"Proxy/Server Departure" sub-option in RS messages with the MSIDs of
the Old FHS/Hub Proxy/Server.)
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 ADM-LLAs 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
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discover the addresses of Proxy/Servers that are geographically and/
or topologically "close" to their underlying network connections.
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 MNP-LLA prefix parameters and/or the DHCPv6 OMNI sub-
option. When the Hub Proxy/Server returns the MNPs, it also creates
a forwarding table entry for the MNP-ULA corresponding to each MNP
resulting in a BGP update (see: Section 3.2.3). For IPv6, the Hub
Proxy/Server creates an IPv6 forwarding table entry for each MNP-ULA.
For IPv4, the Hub Proxy/Server creates an IPv6 forwarding table entry
with the IPv4-compatibility MNP-ULA prefix corresponding to the IPv4
address. The Hub Proxy/Server then returns an RA to the Client via
an FHS Proxy/Server if necessary.
After the initial RS/RA exchange, the Hub Proxy/Server maintains a
ReachableTime timer for each of the Client's underlying 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-ULA 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
underlying interface, the Hub Proxy/Server marks the interface as
DOWN. If ReachableTime expires before any new RS is received on any
individual underlying 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 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
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in the DEPARTED state, the old Hub Proxy/Server forwards any carrier
packets it receives from the secure spanning tree and destined to the
Client to the new Hub Proxy/Server, then deletes the entry after
DepartTime expires.
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 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 underlying
interface. Each of the Client's FHS Proxy/Servers must inform a
single Hub Proxy/Server of the Client's underlying interface(s) that
it services. For Clients on Direct and VPNed underlying interfaces,
the FHS Proxy/Server for each interface is directly connected, for
Clients on ANET underlying interfaces the FHS Proxy/Server is located
on the ANET/INET boundary, and for Clients on INET underlying
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:
o 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 MNP-ULA 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
extension header window synchronization parameters as well as the
Client's observed *NET addresses (noting that they may differ from
the Origin addresses if there were NATs on the path). Proxy/
Server "B" then examines the network-layer destination address.
If the destination address is the ADM-LLA of a different Proxy/
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Server "A", Proxy/Server "B" prepares a separate proxyed version
of the RS message with an OAL header with source set to its own
ADM-ULA and destination set to Proxy/Server B's ADM-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.
o when Hub Proxy/Server "A" receives the RS, it assume the Hub role
and creates or updates a NCE for the Client 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 LLA and destination set to the
Client's MNP-LLA, then encapsulates the RA in an OAL header with
source set to its own ADM-ULA and destination set to the ADM-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.
o when FHS Proxy/Server "B" reassembles the RA, it locates the
Client NCE based on the RA destination LLA. 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. Proxy/Server "B" then re-encapsulates the RA
message with OAL source set to its own ADM-ULA and OAL destination
set to the MNP-ULA of the Client, 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 *NET 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.
o The Client repeats this process over each of its additional
underlying 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.
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 Bridge using OAL encapsulation with its own
ADM-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.
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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
underlying 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 MNP-LLA 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 underlying 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 Bridge via OAL encapsulation. When DepartTime
expires, the Hub Proxy/Server deletes the NCE and discards any
further carrier packets destined to the former Client.
In some ANETs that employ a Proxy/Server, the Client's MNP can be
injected into the ANET routing system. In that case, the Client can
send original IP packets 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 underlying 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 MNP-LLA (or to a Temporary
LLA), and with destination address set to the ADM-LLA 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.
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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 and underlying 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
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
ADM-LLA as the source and the ADM-LLA 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
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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 ADM-LLA of the
new Hub).
3.12.3.3. DHCPv6-Based Prefix Registration
When a Client is not pre-provisioned with an MNP-LLA, 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 the unspecified
address (::) and with an OMNI option that includes a DHCPv6 message
sub-option with DHCPv6 Prefix Delegation (DHCPv6-PD) parameters.
When the Hub Proxy/Server receives the RS message, it extracts the
DHCPv6-PD message from the OMNI option.
The Hub Proxy/Server then acts as a "Proxy DHCPv6 Client" in a
message exchange with the locally-resident DHCPv6 server, which
delegates MNPs and returns a DHCPv6-PD Reply message. (If the Hub
Proxy/Server wishes to defer creation of MN state until the DHCPv6-PD
Reply is received, it can instead act as a Lightweight DHCPv6 Relay
Agent per [RFC6221] by encapsulating the DHCPv6-PD message in a
Relay-forward/reply exchange with Relay Message and Interface ID
options.)
When the Hub Proxy/Server receives the DHCPv6-PD Reply, it adds a
route to the routing system and creates an MNP-LLA based on the
delegated MNP. The Hub Proxy/Server then sends an RA back to the
Client with the (newly-created) MNP-LLA as the destination address
and with the DHCPv6-PD Reply message and OMNI extension header
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 MNP-LLA 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].
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3.13. AERO Route Optimization
AERO nodes invoke route optimization when they need to forward
initial packets to new target destinations and for ongoing multilink
forwarding for current destinations. Route optimization is based on
IPv6 ND Address Resolution messaging between a Route Optimization
Source (ROS) and a Relay or the target Client itself (reached via the
current Hub Proxy/Server) acting as a Route Optimization Responder
(ROR). Route optimization is initiated by the first eligible ROS
closest to the source as follows:
o For Clients on VPNed and Direct interfaces, the Client's FHS
Proxy/Server is the ROS.
o For Clients on ANET interfaces, either the Client or the FHS
Proxy/Server may be the ROS.
o For Clients on INET interfaces, the Client itself is the ROS.
o For correspondent nodes on INET/EUN interfaces serviced by a
Relay, the Relay is the ROS.
o For Clients that engage the Hub Proxy/Server in "mobility anchor"
mode, the Hub Proxy/Server is the ROS.
The AERO routing system directs a route optimization request sent by
the ROS to the ROR, which returns a route optimization reply which
must include information that is current, consistent and authentic.
The ROS is responsible for periodically refreshing the route
optimization, and the ROR is responsible for quickly informing the
ROS of any changes. Following address resolution, the ROS and ROR
perform ongoing multilink route optimizations to maintain optimal
forwarding profiles.
The 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 ROS checks for a NCE with an MNP-LLA that
matches the target destination. If there is a NCE in the REACHABLE
state, the ROS 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 ROS creates one in the INCOMPLETE
state.
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The ROS next prepares an NS message for Address Resolution (NS(AR))
to send toward an ROR 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:
o the LLA of the ROS as the source address.
o the MNP-LLA 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 fe80::2001:db8:1:2.
o 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 OMNI extension header
Preflen set to the prefix length associated with the NS(AR) source.
The ROS also includes Interface Attributes and Traffic Selectors for
all of the source Client's underlying 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 {ADM,MNP}-ULA and OAL destination set to the
MNP-ULA corresponding to the target and with window synchronization
parameters. The ROS then inserts a fragment header, performs
fragmentation and *NET encapsulation, then sends the resulting
carrier packets into the SRT secured spanning tree without
decrementing the network-layer TTL/Hop Limit field.
When the ROS is a Client, it must instead use the ADM-ULA of one of
its FHS Proxy/Servers as the destination. The ROS Client then
fragments, performs *NET 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 ADM-ULA, changes the OAL
destination to the MNP-ULA corresponding to the target, selects an
appropriate Identification, then re-fragments and forwards the
resulting carrier packets into the secured spanning tree on behalf of
the Client.
Note: both the target Client and its Hub Proxy/Server include current
and accurate information for the Client's multilink Interface
Attributes profile. The Hub Proxy/Server can be trusted to provide
an authoritative response on behalf of the Client should the need
arise. While the Client has no such trust basis, any attempt by the
Client to mount an attack by providing false Interface Attributes
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information would only result in black-holing of return traffic,
i.e., the "attack" could only result in denial of service to the
Client itself. Therefore, the Client's asserted Interface Attributes
need not be validated by the Hub Proxy/Server.
3.13.1.1. Relaying the NS(AR) *NET Packet(s)
When the Bridge receives carrier packets containing the NS(AR), it
discards the *NET headers and determines the next hop by consulting
its standard IPv6 forwarding table for the OAL header destination
address. The Bridge then decrements the OAL header Hop-Limit, then
re-encapsulates 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 Bridge will
deliver the carrier packet via the secured spanning tree to the Hub
Proxy/Server (or Relay) that services the target.
3.13.1.2. Processing and Responding to the NS(AR)
When the Hub Proxy/Server for the target receives the NS(AR) secured
carrier packets with the MNP-ULA of the target as the OAL
destination, it reassembles then forwards the message to the target
Client (while including an authentication signature and encapsulation
if necessary) or processes the NS(AR) locally if it is acting as a
Relay/IP router or the Client's designated ROR. The Hub Proxy/Server
processes the message as follows:
o if the NS(AR) target matches a Client NCE in the DEPARTED state,
the (old) Hub Proxy/Server re-encapsulates by setting the OAL
destination address to the ADM-ULA of the Client's new Hub Proxy/
Server. The old Hub Proxy/Server then re-fragments and re-
encapsulates, then forwards the resulting carrier packets over the
secured spanning tree.
o If the NS(AR) target matches the MNP-LLA of a Client NCE in the
REACHABLE state, the Hub Proxy/Server notes whether the NS(AR)
arrived from the secured spanning tree then sets the OAL
destination address to the MNP-ULA of the Client or the ADM-ULA of
the selected FHS Proxy/Server for the Client. If the message
arrived via the secured spanning tree the Hub Proxy/Server
verifies the checksum; otherwise, it must verify the message
authentication signature before forwarding. When the Hub Proxy/
Server determines the underlying interface for the target Client,
it then changes the OAL destination to the ADM-ULA of the target
Client's FHS Proxy/Server, re-fragments and forwards the resulting
carrier packets into the secured spanning tree. When the FHS
Proxy/Server receives the carrier packets, it reassembles and
verifies the checksum, then includes an authentication signature
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if necessary, changes the OAL source to its own ADM-ULA and
destination to the MNP-ULA of the target Client, includes an
Identification value within the current window, then re-fragments
and forwards the resulting carrier packets to the target Client
ROR. (Note that if the Hub and FHS Proxy/Server are one and the
same the Hub itself will perform the FHS procedures.)
o If the NS(AR) target matches one of its non-MNP routes, the Hub
Proxy/Server serves as both a Relay and a ROR, since the Relay
forwards IP packets toward the (fixed network) target at the
network layer.
The ROR then creates a NCE for the NS(AR) LLA 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 ROS with the
source address set to its own MNP-LLA, the destination address set to
the NS(AR) LLA source address and the Target Address set to the same
value that appeared in the NS(AR) Target Address. The ROR includes
an OMNI option with OMNI extension header Preflen set to the prefix
length associated with the NA(AR) source address.
The ROR then 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 ROR finally submits the NA(AR)
for OAL encapsulation with source set to its own ULA and destination
set to either the ULA corresponding to the NS(AR) source or the ADM-
ULA of its FHS Proxy/Server, selects an appropriate Identification,
and includes window synchronization parameters and authentication
signature or checksum. The ROR then includes Interface Attributes
and Traffic Selector sub-options for all of the target's underlying
interfaces with current information for each interface, fragments and
encapsulates each fragment in appropriate *NET headers, then forwards
the resulting (*NET-encapsulated) carrier packets to the FHS Proxy/
Server.
When the FHS Proxy/Server receives the carrier packets, it
reassembles if necessary and verifies the authentication signature or
checksum. The FHS Proxy/Server then changes the OAL source address
to its own ADM-ULA, changes the destination to the {ADM,MNP}-ULA
corresponding to the NA(AR) LLA destination, includes an appropriate
Identification, then fragments and forwards the carrier packets into
the secured spanning tree.
Note: If the Hub Proxy/Server is acting as the Client's ROR but not
as a Relay/IP router (i.e., by virtue of receipt of an RS message
with the A flag set), it prepares the NS(AR) with the R flag set to 0
but without setting the SYN flag in the OMNI extension header window
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synchronization parameters. This informs the ROS that it must
initiate multilink route optimization to synchronize with the Client
either directly or via a FHS Proxy/Server (see: Section 3.13.2).
3.13.1.3. Relaying the NA(AR)
When the Bridge receives NA(AR) carrier packets, it discards the *NET
header and determines the next hop by consulting its standard IPv6
forwarding table for the OAL header destination address. The Bridge
then decrements the OAL header Hop-Limit, re-encapsulates the carrier
packet and forwards it via the SRT secured spanning tree, where it
may traverse multiple OMNI link segments. The final-hop Bridge will
deliver the carrier packet via the secured spanning tree to a Proxy/
Server for the ROS.
3.13.1.4. Processing the NA(AR)
When the ROS receives the NA(AR) message, it first searches for a NCE
that matches the NA(AR) target address. The ROS then processes the
message the same as for standard IPv6 Address Resolution [RFC4861].
In the process, it caches all OMNI option information in the target
NCE (including all Interface Attributes), and caches the NA(AR) MNP-
LLA source address as the address of the target Client.
When the ROS 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 ADM-ULA as the OAL source and the MNP-ULA
of the Client as the OAL destination.
3.13.2. Multilink Route Optimization
Following address resolution, the ROS and ROR can assert multilink
paths through underlying interface pairs serviced by the same source/
destination LLAs by sending unicast NS/NA messages with Multilink
Forwarding Parameters and OMNI extension header window
synchronization parameters when necessary. The unicast NS/NA
messages establish multilink forwarding state in intermediate nodes
in the path between the ROS and ROR.
To support multilink route optimization, OMNI interfaces include an
additional forwarding table termed the Multilink Forwarding
Information Base (MFIB) that supports carrier packet forwarding based
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on OMNI neighbor underlying interface pairs. The MFIB contains
Multilink Forwarding Vectors (MFVs) indexed by 4-octet values known
as MFV Indexes (MFVIs).
OAL source, intermediate and destination nodes create MFVs/MFVIs when
they process an NS message with a Multilink Forwarding Parameters
sub-option with Job code "00" (Initialize; Build B) or a solicited NA
with Job code "01" (Follow B; Build A) (see:
[I-D.templin-6man-omni]). The OAL source of the NS (and OAL
destination of the solicited NA) are considered to reside in the
"First Hop Segment (FHS)", while the OAL destination of the NS (and
OAL source of the solicited NA) are considered to reside in the "Last
Hop Segment (LHS)".
When an OAL node processes an NS with Job code "00", it creates an
MFV, records the NS source and destination ULAs and assigns a "B"
MFVI. When the "B" MVFI is referenced, the MVF retains the ULAs in
(dst,src) order the opposite of how they appeared in the original NS
to support full header reconstruction. (If the NS message included a
nested OAL encapsulation, the ULAs of both OAL headers are retained.)
When an OAL node processes a solicited NA with Job code "01", it
locates the MFV created by the NS and assigns an "A" MFVI. When the
"A" MFVI is referenced, the MFV retains the ULAs in (src,dst) order
the same as they appeared in the original NS to support full header
reconstruction. (If the NS message included a nested OAL
encapsulation, the ULAs of both OAL headers are retained.)
OAL nodes generate random 32-bit values as candidate A/B MFVIs which
must first be tested for local uniqueness. If a candidate MFVI s
already in use (or if the value is 0), 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; also, an MFVI generated by a first OAL
node is never tested for uniqueness on other OAL nodes, since the
uniqueness property is node-local only.)
OAL nodes maintain A/B MFVIs as follows:
o "B1" - a locally-unique MFVI maintained independently by each OAL
node on the path from the FHS OAL source to the last OAL
intermediate node before the LHS OAL destination. The OAL node
generates and assigns a "B1" MFVI to a newly-created MFV when it
processes an NS message with Job code "00". When the OAL node
receives future carrier packets that include this value, it can
unambiguously locate the correct MFV and determine directionality
without examining addresses.
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o "A1" - a locally unique MFVI maintained independently by each OAL
node on the path from the LHS OAL source to the last OAL
intermediate node before the FHS OAL destination. The OAL node
generates and assigns an "A1" MFVI to the MVF that configures the
corresponding "B1" MFVI when it processes a solicited NA message
with Job code "01". When the OAL node receives future carrier
packets that include this value, it can unambiguously locate the
correct MFV and determine directionality without examining
addresses.
o "A2" - the A1 MFVI of a remote OAL node discovered by an FHS OAL
source or OAL intermediate node when it processes an NA message
with Job code "01" that originated from an LHS OAL source. A2
values MUST NOT be tested for uniqueness within the OAL node's
local context.
o "B2" - the B1 MFVI of a remote OAL node discovered by an LHS OAL
source or OAL intermediate node when it processes an NS message
with Job code "00" that originated from an FHS OAL source. B2
values MUST NOT be tested for uniqueness within the OAL node's
local context.
When an FHS OAL source has an original IP packet to send to an LHS
OAL destination discovered via multilink address resolution, it first
selects a source and target underlying interface pair. The OAL
source uses its cached information for the target underlying
interface as LHS information then prepares an NS message with an OMNI
Multilink Forwarding Parameters sub-option with Job code "00" and
with source set to its own {ADM,MNP}-LLA. If the LHS FMT-Forward and
FMT-Mode bits are both clear, the OAL source sets the destination to
the ADM-LLA of the LHS Proxy/Server; otherwise, it sets the
destination to the MNP-LLA of the target Client. The OAL source then
sets window synchronization information in the OMNI extension header
and updates/creates a NCE for the selected destination {ADM,MNP}-LLA
in the INCOMPLETE state. The OAL source next creates an MFV based on
the NS source and destination LLAs, then generates a "B1" MFVI and
assigns it to the MFV while also including it as the first B entry in
the MFVI List. The OAL source then populates the NS Multilink
Forwarding Parameters based on any FHS/LHS information it knows
locally. OAL intermediate nodes on the path to the OAL destination
may populate additional FHS/LHS information on a hop-by-hop basis.
If the OAL source is the FHS Proxy/Server, it then performs OAL
encapsulation/fragmentation while setting the source to its own ADM-
ULA and setting the destination to the FHS Subnet Router Anycast ULA
determined by applying the FHS SRT prefix length to its ADM-ULA. The
FHS Proxy/Server next examines the LHS FMT code. If FMT-Forward is
clear and FMT-Mode is set, the FHS Proxy/Server checks for a NCE for
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the ADM-LLA 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 OMNI Multilink Forwarding
Parameters Tunnel Window Synchronization fields. The FHS Proxy/
Server then selects an appropriate Identification value and *NET
headers and forwards the resulting carrier packets into the secured
spanning tree which will deliver them to a Bridge interface that
assigns the FHS Subnet Router Anycast ULA.
If the OAL source is the FHS Client, it instead includes an
authentication signature if necessary, performs OAL encapsulation,
sets the source to its own MNP-ULA, sets the destination to
{ADM,MNP}-ULA of the FHS Proxy/Server and selects an appropriate
Identification value for the FHS Proxy/Server. If FHS FMT-Forward is
set and LHS FMT-Forward is clear, the FHS Client creates/updates a
NCE for the ADM-LLA of the LHS Proxy/Server as above and includes
Tunnel Window Synchronization parameters. The FHS Client then
fragments and encapsulates in appropriate *NET headers then forwards
the carrier packets to the FHS Proxy/Server. When the FHS Proxy/
Server receives the carrier packets, it verifies the Identification,
reassembles/decapsulates to obtain the NS then verifies the
authentication signature or checksum. The FHS Proxy/Server then
creates an MFV (i.e., the same as the FHS Client had done) while
assigning the current B entry in the MFVI List (i.e., the one
included by the FHS Client) as the "B2" MFVI for this MVF. The FHS
Proxy/Server next generates a new unique "B1" MFVI, then both assigns
it to the MFV and writes it as the next B entry in the OMNI Multilink
Forwarding Parameters 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 whether to create a NCE
for the LHS Proxy/Server ADM-LLA and include Tunnel Window
Synchronization parameters the same as above. The FHS Proxy/Server
then calculates the checksum, re-fragments while setting the OAL
source address to its own ADM-ULA and destination address to the FHS
Subnet Router Anycast ULA, and includes an Identification appropriate
for the secured spanning tree. The FHS Proxy/Server finally includes
appropriate *NET headers and forwards the carrier packets into the
secured spanning tree the same as above.
Bridges 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 Bridge receives a carrier packet over the secured spanning
tree addressed to its ADM-ULA or the FHS Subnet Router Anycast ULA,
it instead reassembles/decapsulates to obtain the NS then verifies
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the checksum. The FHS Bridge next creates an MFV (i.e., the same as
the FHS Proxy/Server had done) while assigning the current B entry in
the MFVI List as the MFV "B2" index. The FHS Bridge also caches the
NS Multilink Forwarding Parameters FHS information in the MFV, and
also caches the first B entry in the MFVI List as "FHS-Client" when
FHS FMT-Forward/Mode are both set to enable future direct forwarding
to this FHS Client. The FHS Bridge then generates a "B1" MFVI for
the MFV and also writes it as the next B entry in the NS's MFVI List.
The FHS Bridge then examines the SRT prefixes corresponding to both
FHS and LHS. If the FHS Bridge has a local interface connection to
both the FHS and LHS (whether they are the same or different
segments), the FHS/LHS Bridge caches the NS LHS information, writes
its ADM-ULA suffix and LHS INADDR into the NS OMNI Multilink
Forwarding Parameters LHS fields, then sets its own ADM-ULA as the
source and the ADM-ULA of the LHS Proxy/Server as the destination
while selecting an appropriate identification. If the FHS and LHS
prefixes are different, the FHS Bridge instead sets the LHS Subnet
Router Anycast ULA as the destination. The FHS Bridge then
recalculates the NS checksum, selects an appropriate Identification
and *NET headers as above then forwards the carrier packets into the
secured spanning tree.
When the FHS and LHS Bridges are different, the LHS Bridge will
receive carrier packets over the secured spanning tree from the FHS
Bridge. The LHS Bridge reassembles/decapsulates to obtain the NS
then verifies the checksum and creates an MFV (i.e., the same as the
FHS Bridge had done) while assigning the current B entry in the MFVI
List as the MFV "B2" index. The LHS Bridge also caches the ADM-ULA
of the FHS Bridge found in the Multilink Forwarding Parameters as the
spanning tree address for "B2", caches the NS Multilink Forwarding
Parameters LHS information then generates a "B1" MFVI for the MFV
while also writing it as the next B entry in the MFVI List. The LHS
Bridge also writes its own ADM-ULA suffix and LHS INADDR into the
OMNI Multilink Forwarding Parameters. The LHS Bridge then sets the
its own ADM-ULA as the source and the ADM-ULA of the LHS Proxy/Server
as the OAL destination, recalculates the checksum, selects an
appropriate Identification, then fragments while including
appropriate *NET headers and forwards the carrier packets into the
secured spanning tree.
When the LHS Proxy/Server receives the carrier packets from the
secured spanning tree, it reassembles/decapsulates to obtain the NS,
verifies the checksum 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 assigns the current B entry in the MFVI List as the "B2" MFVI
the same as for the prior hop. If the NS destination is the MNP-LLA
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of the target Client, the LHS Proxy/Server also generates a "B1" 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
ADM-LLA of the FHS Proxy/Server (if necessary) and sets the state to
STALE, then caches any Tunnel Window Synchronization parameters.
If the NS destination is its own ADM-LLA, the LHS Proxy/Server next
prepares to return a solicited NA with Job code "01". If the NS
source was the MNP-LLA of the FHS Client, the LHS Proxy/Server first
creates or updates an NCE for the MNP-LLA with state set to STALE.
The LHS Proxy/Server next caches the NS OMNI extension header window
synchronization parameters and Multilink Forwarding Parameters
information (including the MFVI List) in the NCE corresponding to the
LLA source. When the LHS Proxy/Server forwards future carrier
packets based on the NCE, it can populate reverse-path 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 OMNI Multilink Forwarding Parameters FHS/LHS
information into the corresponding fields in the NA. The LHS Proxy/
Server then generates an "A1" MFVI and both assigns it to the MFV and
includes it as the first A entry in NA's 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 synchronization
parameters in the OMIN extension header (if necessary) and also
tunnel window synchronization parameters in the Multilink Forwarding
Parameters (if necessary). The LHS Proxy/Server then encapsulates
the NA, calculates the checksum, sets the source to its own ADM-ULA,
sets the destination to the ADM-ULA of the LHS Bridge, selects an
appropriate Identification value and *NET headers then forwards the
carrier packets into the secured spanning tree.
If the NS destination was the MNP-LLA 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 ADM-ULA and changes the destination to the MNP-
ULA of the LHS Client. The LHS Proxy/Server then selects an
appropriate Identification value, fragments if necessary, includes
appropriate *NET headers and forwards the carrier packets to the LHS
Client. When the LHS Client receives the carrier packets, it
verifies the Identification and reassembles/decapsulates to obtain
the NS then verifies the authentication signature or checksum. The
LHS Client then creates a NCE for the NS LLA source address in the
STALE state. If LHS FMT-Forward is set, FHS FMT-Forward is clear and
the NS source was an MNP-LLA, the Client also creates a NCE for the
ADM-LLA of the FHS Proxy/Server in the STALE state and caches any
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Tunnel Window Synchronization parameters. The Client then caches the
NS OMNI extension header window synchronization parameters and
Multilink Forwarding Parameters in the NCE corresponding to the NS
LLA source, then creates an MFV and assigns both the current MFVI
List B entry as "B2" and a locally generated "A1" MFVI the same as
for previous hops (the LHS Client also includes the "A1" value in the
solicited NA - see above and below). The LHS Client also caches the
previous MFVI List B entry as "LHS-Bridge" since it can include this
value when it sends future carrier packets directly to the Bridge
(following appropriate neighbor coordination).
The LHS Client then prepares an NA using exactly the same procedures
as for the LHS Proxy/Server above, except that it uses its MNP-LLA as
the source and the {ADM,MNP}-LLA of the FHS correspondent as the
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 MNP-ULA and
destination set to the ADM-ULA of the LHS Proxy/Server, includes an
appropriate Identification and *NET 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/
decapsulates to obtain the NA, verifies the authentication signature
or checksum, then uses the current MVFI List B entry to locate the
MFV. The LHS Proxy/Server then writes the current MFVI List A entry
as the "A2" value for the MVF, generates an "A1" MFVI and both
assigns it to the MFV and writes it as the next 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 recalculates the checksum, re-fragments the NA
while setting the OAL source to its own ADM-ULA and destination to
the ADM-ULA of the LHS Bridge, includes an appropriate Identification
and *NET headers and forwards the carrier packets into the secured
spanning tree.
When the LHS Bridge receives the carrier packets, it reassembles/
decapsulates to obtain the NA while verifying the checksum then uses
the current MFVI List B entry to locate the MFV. The LHS Bridge then
writes the current MFVI List A entry as the MFV "A2" index and
generates a new "A1" value which it both assigns the MFV and writes
as the next MFVI List A entry. (The LHS Bridge also caches the first
A entry in the MFVI List as "LHS-Client" when LHS FMT-Forward/Mode
are both set to enable future direct forwarding to this LHS Client.)
If the LHS Bridge is connected directly to both the FHS and LHS
segments (whether the segments are the same or different), the FHS/
LHS Bridge will have already cached the FHS/LHS information based on
the original NS. The FHS/LHS Bridge recalculates the checksum then
re-fragments the NA while setting the OAL source to its own ADM-ULA
and destination to the ADM-ULA of the FHS Proxy/Server. If the FHS
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and LHS prefixes are different, the FHS Bridge instead re-fragments
while setting the destination to the ADM-ULA of the FHS Bridge. The
LHS Bridge selects an appropriate Identification and *NET headers
then forwards the carrier packets into the secured spanning tree.
When the FHS and LHS Bridges are different, the FHS Bridge will
receive the carrier packets from the LHS Bridge over the secured
spanning tree. The FHS Bridge reassembles/decapsulates to obtain the
NA while verifying the checksum, then locates the MFV based on the
current MFVI List B entry. The FHS Bridge then assigns the current
MFVI List A entry as the MFV "A2" index and caches the ADM-ULA of the
LHS Bridge as the spanning tree address for "A2". The FHS Bridge
then generates an "A1" MVFI and both assigns it to the MVF and writes
it as the next MFVI List A entry while also writing its ADM-ULA and
INADDR in the NA FHS Bridge fields. The FHS Bridge then recalculates
the checksum, re-encapsulates/re-fragments with its own ADM-ULA as
the source, with the ADM-ULA of the FHS Proxy/Server as the
destination, then selects an appropriate Identification value and
*NET headers and forwards the carrier packets into the secured
spanning tree.
When the FHS Proxy/Server receives the carrier packets from the
secured spanning tree, it reassembles/decapsulates to obtain the NA
while verifying the checksum then locates the MFV based on the
current MFVI List B entry. The FHS Proxy/Server then assigns the
current MFVI List A entry as the "A2" MFVI the same as for the prior
hop. If the NA destination is its own ADM-LLA, the FHS Proxy/Server
then caches the NA Multilink Forwarding Parameters with the MFV and
examines LHS FMT. If FMT-Forward is clear, the FHS Proxy/Server
locates the NCE for the ADM-LLA of the LHS Proxy/Server and sets the
state to REACHABLE then caches any Tunnel Window Synchronization
parameters. If the NA source is the MNP-LLA of the LHS Client, the
FHS Proxy/Server then locates the LHS Client NCE and sets the state
to REACHABLE then caches the OMNI extension header window
synchronization parameters and prepares to return an NA
acknowledgement, if necessary.
If the NA destination is the MNP-LLA of the FHS Client, the FHS
Proxy/Server also searches for and updates the NCE for the ADM-LLA of
the LHS Proxy/Server if necessary the same as above. The FHS Proxy/
Server then generates an "A1" MFVI and assigns it both to the MFVI
and as the next 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 ADM-LA and sets the destination to the
MNP-ULA of the FHS Client, then selects an appropriate Identification
value and *NET headers and forwards the carrier packets to the FHS
Client.
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When the FHS Client receives the carrier packets, it verifies the
Identification, reassembles/decapsulates to obtain the NA, verifies
the authentication signature or checksum, then locates the MFV based
on the current MFVI List B entry. The FHS Client then assigns the
current MFVI List A entry as the "A2" MFVI the same as for the prior
hop. The FHS Client then caches the NA Multilink Forwarding
Parameters (including the MFVI List) with the MFV and examines LHS
FMT. If FMT-Forward is clear, the FHS Client locates the NCE for the
ADM-LLA of the LHS Proxy/Server and sets the state to REACHABLE then
caches any Tunnel Window Synchronization parameters. If the NA
source is the MNP-LLA of the LHS Client, the FHS Proxy/Server then
locates the LHS Client NCE and sets the state to REACHABLE then
caches the OMNI extension header window synchronization parameters
and prepares to return an NA acknowledgement, if necessary. The FHS
Client also caches the previous MFVI List A entry as "FHS-Bridge"
since it can include this value when it sends future carrier packets
directly to the Bridge (following appropriate neighbor coordination).
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 OMNI Multilink Forwarding Parameters 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 source to its own {ADM,MNP}-
LLA, sets the destination to the {ADM,MNP}-LLA of the LHS node then
includes Tunnel Window Synchronization parameters if necessary. The
FHS node next sets the 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 {ADM,MNP}-ULA as the source. If the FHS node
is the Client, it next sets the ADM-ULA of the FHS Proxy/Server as
the OAL destination, includes an authentication signature or
checksum, selects an appropriate Identification value and *NET
headers and forwards the carrier packets to the FHS Proxy/Server.
The FHS Proxy/Server then verifies the Identification, reassembles/
decapsulates, verifies the authentication signature or checksum, then
uses the current MFVI List A entry to locate the MFV. The FHS Proxy/
Server then writes its "B1" MFVI as the next 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.
The FHS Proxy/Server recalculates the uNA checksum then re-fragments
while setting its own ADM-ULA as the source and the ADM-ULA of the
FHS Bridge as the destination, then selects an appropriate
Identification and *NET headers and forwards the carrier packets into
the secured spanning tree. When the FHS Bridge receives the carrier
packets, it reassembles/decapsulates to obtain the uNA while
verifying the checksum then uses the current MFVI List A entry to
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locate the MFV. The FHS Bridge then writes its "B1" MFVI as the next
MFVI List B entry, then re-fragments while setting the OAL source and
destination. If the FHS Bridge is also the LHS Bridge, it sets the
ADM-ULA of the LHS Proxy/Server as the destination; otherwise it sets
the ADM-ULA of the LHS Bridge. The FHS Bridge recalculates the
checksum then selects an appropriate Identification and *NET headers,
re-fragments/forwards the carrier packets into the secured spanning
tree. If an LHS Bridge receives the carrier packets, it processes
them exactly the same as the FHS Bridge had done while setting the
carrier packet destination to the ADM-ULA of the LHS Proxy/Server.
When the LHS Proxy/Server receives the carrier packets, it
reassembles/decapsulates to obtain the uNA message while verifying
the checksum. The LHS Proxy/Server then locates the MFV based on the
current MFVI List A entry then determines whether it is a tunnel
ingress the same as for the original NS. If it is a tunnel ingress,
the LHS Proxy/Server updates the NCE for the tunnel far-end based on
the Tunnel Window Synchronization parameters. If the uNA destination
is its own ADM-LLA, the LHS Proxy/Server next updates the NCE for the
source LLA based on the OMNI extension header 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 MNP-LLA of the LHS Client, the LHS
Proxy/Server instead writes its "B1" MFV as the next MFVI List B
entry, includes an authentication signature or checksum, writes its
own ADM-ULA as the source and the MNP-ULA of the Client as the
destination then selects an appropriate Identification and *NET
headers and forwards the resulting carrier packets to the LHS Client.
When the LHS Client receives the carrier packets, it verifies the
Identification, reassembles/decapsulates to obtain the uNA, verifies
the authentication signature or checksum then processes the message
exactly the same as for the LHS Proxy/Server case above.
Following the NS/NA exchange with Multilink Forwarding Parameters,
OAL end systems and tunnel endpoints can begin exchanging ordinary
carrier packets with Identification values within their respective
send/receive windows without requiring security signatures and/or
secured spanning tree traversal. Either peer can refresh window
synchronization parameters and/or send other carrier packets
requiring security at any time using the same secured procedures
described above. OAL end systems and intermediate nodes can also use
their own A1/B1 MFVIs when they receive carrier packets to
unambiguously locate the correct MFV and determine directionality and
can use any discovered A2/B2 MFVIs to forward carrier packets to
other OAL nodes that configure the corresponding A1/B1 MFVIs. When
an OAL node uses an MFVI included in a carrier packet to locate an
MFV, it need not also examine the carrier packet addresses.
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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 also begin
forwarding carrier packets with OAL compressed headers termed "OCH-
0/1" (Type 0 or 1) (see: [I-D.templin-6man-omni]) that include only a
single A/B MFVI meaningful to the next hop, since all nodes in the
path up to (and sometimes including) the OAL destination have already
established MFV forwarding information. Note that when an FHS OAL
source receives a solicited NA with Job code "01', the message 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 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-0/1 header based on the intended OAL intermediate node or
destination.
When a Bridge receives unsecured carrier packets destined to a local
segment Client that has asserted direct reachability, the Bridge
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
Bridge instead forwards carrier packets directly to the local Proxy/
Server.
When a Proxy/Server receives carrier packets destined to a local
Client or forwards carrier packets received from a local 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 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 an MNP-ULA source and
CRH-32 routing header, or an OCH-0/1 header with an MFVI that matches
an MFV, the ingress encapsulates the carrier packet in a new full OAL
header or an OCH-0/1 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
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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.
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 match 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 underlying 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 Bridge (following the establishment of INADDR information) while
bypassing the Proxy/Server (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.
After window synchronization state has been established, the ROS and
ROR can begin forwarding carrier packets while performing additional
NS/NA exchanges as above to update window state, register new
interface pairs for optimized multilink forwarding and/or confirm
reachability. The ROS sends carrier packets to the FHS Bridge
discovered through the NS/NA exchange. The FHS Bridge then forwards
the carrier packets over the unsecured spanning tree to the LHS
Bridge, which forwards them via LHS encapsulation to the LHS Proxy/
Server or directly to the target Client itself. The target Client in
turn sends packets to the ROS in the reverse direction while
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forwarding through the Bridges to minimize Proxy/Server load whenever
possible.
While the ROS continues to actively forward packets to the target
Client, it is responsible for updating window synchronization state
and per-interface reachability before expiration. Window
synchronization state is shared by all underlying interfaces in the
ROS' NCE that use the same destination LLA so that a single NS/NA
exchange applies for all interfaces regardless of the specific
interface used to conduct the exchange. However, the window
synchronization exchange only confirms target Client reachability
over the specific underlying interface pair. Reachability for other
underlying interfaces that share the same window synchronization
state must be determined individually using additional NS/NA
messages.
3.13.3. Rapid Commit Route Optimization
When the ROR 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 ROR prepares a
unicast NS message with an OMNI option with window synchronization
information responsive to the NS(AR), with a Multilink Forwarding
Parameters sub-option selected for a specific underlying interface
pair and with Interface Attributes for all of the ROR's other
underlying interfaces. The ROR can also include ordinary IP packets
as OAL super-packet extensions to the NS message if it has immediate
data to send to the ROS. The ROR then returns the NS to the ROS the
same as for the NA(AR) case.
When the NS message traverses the return path to the ROR, 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 ROS, 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 ROS then completes the route optimization by returning a
responsive NA.
Note: The ROS 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).
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3.13.4. Client/Bridge Route Optimization
Following multilink route optimization for specific underlying
interface pairs, ROS/ROR Clients located on open INETs can invoke
Client/Bridge route optimization to improve performance and reduce
load and congestion on their respective FHS/LHS Proxy/Servers. To
initiate Client/Bridge route optimization, the Client prepares an NS
message with its own MNP-LLA address as the source and the ADM-LLA of
its Bridge as the destination while creating a NCE for the Bridge 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
underlying interface as well as an authentication signature but does
not include window synchronization parameters. The Client then
performs OAL encapsulation with its own MNP-ULA as the source and the
ADM-ULA of the Bridge as the destination while including a randomly-
chosen Identification value, then performs *NET encapsulation on the
atomic fragment and sends the resulting carrier packet directly to
the Bridge.
When the Bridge receives the carrier packet, it verifies the
authentication signature then creates a NCE for the Client. The
Bridge then caches the *NET 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
underlying interface as "trusted". The Bridge then prepares an NA
reply with its own ADM-LLA as the source and the MNP-LLA of the
Client as the destination where the NA again must be no larger than
the minimum MPS.
The Bridge then echoes the Client's Interface Attributes, includes an
Origin Indication with the Client's observed *NET addresses and
includes an authentication signature. The Bridge then performs OAL
encapsulation with its own ADM-ULA as the source and the MNP-ULA of
the Client as the destination while using the same Identification
value that appeared in the NS, then performs *NET 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
*NET source address information as the Bridge target address via this
underlying interface while marking the interface as "trusted". The
Client also caches the Origin Indication *NET address information as
its own (external) source address for this underlying interface.
After the Client and Bridge have established NCEs as well as
"trusted" status for a particular underlying interface pair, each
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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 Bridge 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 underlying interface pair status becomes "untrusted".
Thereafter, when the Client forwards a carrier packet with an MFVI
toward the Bridge as the next hop, the Client uses the MFVI for the
Bridge (discovered during multilink route optimization) instead of
the MFVI for its Proxy/Server; the Bridge will accept the packet from
the Client if and only if the underlying interface status is trusted
and if the MFVI is correct for the next hop toward the final
destination. (The same is true in the reverse direction when the
Bridge sends carrier packets directly to the Client.)
Note that the Client and Bridge each maintain a single NCE, but that
the NCE may aggregate multiple underlying interface pairs. Each
underlying interface pair may use differing source and target *NET
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 Bridges 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 ADM-LLA of the Bridge, and the Proxy/Server and Bridge could
relay the messages over the secured spanning tree. However, this
would still require the Client to send additional messages toward the
*NET address of the Bridge to populate NAT state; hence the savings
in complexity for Bridges would result in increased message overhead
for Clients.
3.13.5. Client/Client Route Optimization
When the ROS/ROR 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
Bridge) and can begin forwarding packets directly via NAT traversal
while avoiding any Proxy/Server and/or Bridge hops.
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When the ROR/ROS Clients on the same SRT segment perform the initial
NS/NA exchange to establish Multilink Forwarding state, they also
include an Origin Indication (i.e., in addition to Multilink
Forwarding Parameters) 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 *NET address for the target Client
which primes its local chain of NATs for reception of future packets
from that *NET address (see: [RFC4380] and [I-D.templin-6man-omni]).
The source Client then prepares an NS message with its own MNP-LLA as
the source, with the MNP-LLA 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
MNP-ULA as the source, with the MNP-ULA of the target Client as the
destination and with an in-window Identification for the target. The
source Client then fragments and encapsulates in *NET headers
addressed to its FHS Proxy/Server then forwards the resulting carrier
packets to the Proxy/Server.
When the FHS Proxy/Server receives the carrier packets, it re-
encapsulates and forwards them as unsecured carrier packets according
to MFV 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 MNP-LLA as the source,
with the MNP-LLA 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 MNP-ULA
as the source, with the MNP-ULA of the source Client as the
destination and with an in-window Identification for the source
Client. The target Client then fragments and encapsulates in *NET
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) underlying 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 Bridges, 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.
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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
underlying 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.
3.14. 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 LLAs and ULAs
of the parties involved in the NUD test. When only reachability
information is required without updating any other NCE state, AERO
nodes can instead perform NS/NA(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 an ROR directs an ROS to a target neighbor with one or more
link-layer addresses, either node may invoke multilink forwarding
state initialization to establish authentic intermediate node state
between specific underlying interface pairs which also tests their
reachability. Thereafter, either node acting as the source may
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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 underlying interface of the target
itself. While testing a target underlying 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 the LLA of the source and
either the ADM-LLA of the LHS Proxy/Server or the MNP-LLA 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 underlying 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 Bridge in the
local segment.
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 LLAs 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 underlying
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
Bridge in the local segment.
When the source receives the NA(NUD), it marks the target underlying
interface tested as "trusted". Note that underlying interface states
are maintained independently of the overall NCE REACHABLE state, and
that a single NCE may have multiple target underlying interfaces in
various "trusted/untrusted" states while the NCE state as a whole
remains REACHABLE.
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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 underlying
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 underlying interface.
Mobility management considerations are specified in the following
sections.
3.15.1. Mobility Update Messaging
RORs and ROSs accommodate Client mobility and/or multilink change
events by sending secured uNA messages to each active neighbor. When
an ROR/ROS sends a uNA message, it sets the IPv6 source address to
the its own LLA, sets the destination address to the neighbor's
{ADM,MNP}-LLA and sets the Target Address to the Client's MNP-LLA.
The ROR/ROS also includes an OMNI option with OMNI extension header
Preflen set to the prefix length associated with the Client's MNP-
LLA, includes Interface Attributes and Traffic Selectors for the
Client's underlying interfaces and includes an authentication
signature if necessary. The ROR 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 its FHS
Proxy/Server's ADM-ULA. When the FHS Proxy/Server receives the uNA,
it reassembles, verifies the authentication signature, then changes
the destination to the ULA corresponding to the LLA destination and
forwards the uNA into the secured spanning tree.
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
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uNA messages will be delivered with high probability, but in any case
the ROR/ROS 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 ROR/ROS 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 ROR/ROS Proxy/Server receives a uNA message prepared as
above, if the uNA destination was its own ADM-LLA 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 MNP-LLA of the
ROR/ROS Client, the Proxy/Server instead changes the OAL source to
its own ADM-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].
3.15.2. Announcing Link-Layer Information Changes
When a Client needs to change its underlying 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 underlying
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.
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3.15.3. Bringing New Links Into Service
When a Client needs to bring new underlying 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 underlying
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 underlying 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 underlying interface
other than the one being deactivated, it MUST include Interface
Attributes with appropriate link quality values for any underlying
interfaces being deactivated. The Client then again sends uNA
messages to all neighbors the same as described above.
Note that when a Client deactivates an underlying interface,
neighbors that receive the ensuing uNA messages need not purge all
references for the underlying interface from their neighbor cache
entries. The Client may reactivate or reuse the underlying 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 underlying interfaces with the new Hub while
including the 32 least significant bits of the old Hub's ADM-LLA in
the "Old Hub Proxy/Server MSID" 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 MSID is
non-zero and different from its own). The uNA has the MNP-LLA of the
Client as the source and the ADM-LLA of the old hub as the
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destination and with OMNI extension header Preflen set to 0. The FHS
Proxy/Server encapsulates the uNA in an OAL header with the ADM-ULA
of the new Hub as the source and the ADM-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 ADM-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 MNP-ULA to the new Hub Proxy/Server's ADM-
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 underlying interface at any time such that a
Client RS/RA exchange over the underlying 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 an MSID for the "Old FHS
Proxy/Server MSID", and the new FHS Proxy/Server will issue a uNA
using the same procedures as outlined for the Hub above while using
its own ADM-ULA as the source address. This can often result in
successful delivery of packets that would otherwise be lost due to
the mobility event.
Clients SHOULD NOT move rapidly between Hub Proxy/Servers in order to
avoid causing excessive oscillations in the AERO routing system.
Examples of when a Client might wish to change to a different Hub
Proxy/Server include a Hub Proxy/Server that has 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 EUNs 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 underlying 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
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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 ROS to send NS(AR) messages to an
ROR for the multicast source. Clients on INET and ANET underlying
interfaces without native multicast services instead send NS(AR)
messages as an ROS to cause their FHS Proxy/Server forward the
message to an ROR. When the ROR 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 ROS "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 LLA as the
source address, the solicited node multicast address corresponding to
S as the destination and the LLA of S as the target address. X then
encapsulates the NS(AR) in an OAL header with source address set to
its own ULA and destination address set to the ULA for S, then
forwards the message into the secured spanning tree which delivers it
to ROR "Y" that services S. The resulting NA(AR) will return an OMNI
option with Interface Attributes for any underlying interfaces that
are currently servicing S.
When X processes the NA(AR) it selects one or more underlying
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 LLA of X as the next hop in
the reverse path. Since Bridges 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
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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 LLA for source S and sends new Join messages
in NS/NA exchanges addressed to the new target Client underlying
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 ROS 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 LLA as the source address and the LLA for
R as the destination address, then encapsulates the NS message in an
OAL header with its own ULA as the source and the ADM-ULA of R's
Proxy/Server as the destination then sends the message into the
secured spanning tree.
For each source S that sends multicast traffic to group G via R,
Client S* that aggregates S (or its Proxy/Server) encapsulates the
original IP packets 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.
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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 Bridges 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).
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 Bridges.
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 Bridges on the link. Correspondent nodes
can then perform Segment Routing to select the correct SRT, which
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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 Bridges on each INET partition, with each Bridge
distributing its MNPs and/or discovering non-MNP IP GUA prefixes on
its INET links.
This gives rise to the opportunity to eventually distribute native IP
addresses to all nodes, and to present a unified OMNI link view even
if the INET partitions remain in their current protocol and
addressing plans. In that way, the OMNI link can serve the dual
purpose of providing a mobility/multilink service and a transition/
coexistence service. Or, if an INET partition is transitioned to a
native IP protocol version and addressing scheme that is compatible
with the OMNI link MNP-based addressing scheme, the partition and
OMNI link can be joined by Bridges.
Relays that connect INETs/EUNs with dissimilar IP protocol versions
may need to employ a network address and protocol translation
function such as NAT64 [RFC6146].
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3.20. Proxy/Server-Bridge Bidirectional Forwarding Detection
In environments where rapid failure recovery is required, Proxy/
Servers and Bridges 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 Bridges maintain BFD sessions in parallel with
their BGP peerings. If a Proxy/Server or Bridge fails, BGP peers
will quickly re-establish routes through alternate paths the same as
for common BGP deployments. Similarly, Proxys maintain BFD sessions
with their associated Bridges even though they do not establish BGP
peerings with them.
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
its MNP-LLA) 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.
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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 Bridges 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 Bridges of all OMNI link
segments in turn configure secured tunnels for their neighboring AERO
Bridges 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.
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
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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 Bridges present targets for traffic
amplification Denial of Service (DoS) attacks. This concern is no
different than for widely-deployed VPN security gateways in the
Internet, where attackers could send spoofed packets to the gateways
at high data rates. This can be mitigated through the AERO/OMNI data
origin authentication procedures, as well as connecting Proxy/Servers
and Bridges 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
EUNs to gain access to a protected network, i.e., AERO Clients that
act as routers MUST NOT provide routing services for unauthorized
nodes. (This concern is no different than for ordinary hosts that
receive an IP address delegation but then "share" the address with
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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, OMNI 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.
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, 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.
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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
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:
o The Internet Routing Overlay Network (IRON)
[RFC6179][I-D.templin-ironbis]
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o Virtual Enterprise Traversal (VET)
[RFC5558][I-D.templin-intarea-vet]
o The Subnetwork Encapsulation and Adaptation Layer (SEAL)
[RFC5320][I-D.templin-intarea-seal]
o 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
[I-D.templin-6man-omni]
Templin, F. L. and T. Whyman, "Transmission of IP Packets
over Overlay Multilink Network (OMNI) Interfaces", draft-
templin-6man-omni-51 (work in progress), November 2021.
[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>.
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[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>.
[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>.
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[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/info/rfc8200>.
[RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A.,
Richardson, M., Jiang, S., Lemon, T., and T. Winters,
"Dynamic Host Configuration Protocol for IPv6 (DHCPv6)",
RFC 8415, DOI 10.17487/RFC8415, November 2018,
<https://www.rfc-editor.org/info/rfc8415>.
8.2. Informative References
[BGP] Huston, G., "BGP in 2015, http://potaroo.net", January
2016.
[I-D.bonica-6man-comp-rtg-hdr]
Bonica, R., Kamite, Y., Alston, A., Henriques, D., and L.
Jalil, "The IPv6 Compact Routing Header (CRH)", draft-
bonica-6man-comp-rtg-hdr-27 (work in progress), November
2021.
[I-D.bonica-6man-crh-helper-opt]
Li, X., Bao, C., Ruan, E., and R. Bonica, "Compressed
Routing Header (CRH) Helper Option", draft-bonica-6man-
crh-helper-opt-04 (work in progress), October 2021.
[I-D.ietf-intarea-frag-fragile]
Bonica, R., Baker, F., Huston, G., Hinden, R. M., Troan,
O., and F. Gont, "IP Fragmentation Considered Fragile",
draft-ietf-intarea-frag-fragile-17 (work in progress),
September 2019.
[I-D.ietf-intarea-tunnels]
Touch, J. and M. Townsley, "IP Tunnels in the Internet
Architecture", draft-ietf-intarea-tunnels-10 (work in
progress), September 2019.
[I-D.ietf-ipwave-vehicular-networking]
(editor), J. (. J., "IPv6 Wireless Access in Vehicular
Environments (IPWAVE): Problem Statement and Use Cases",
draft-ietf-ipwave-vehicular-networking-24 (work in
progress), October 2021.
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[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", draft-ietf-
rtgwg-atn-bgp-11 (work in progress), July 2021.
[I-D.templin-6man-dhcpv6-ndopt]
Templin, F. L., "A Unified Stateful/Stateless
Configuration Service for IPv6", draft-templin-6man-
dhcpv6-ndopt-11 (work in progress), January 2021.
[I-D.templin-intarea-seal]
Templin, F. L., "The Subnetwork Encapsulation and
Adaptation Layer (SEAL)", draft-templin-intarea-seal-68
(work in progress), January 2014.
[I-D.templin-intarea-vet]
Templin, F. L., "Virtual Enterprise Traversal (VET)",
draft-templin-intarea-vet-40 (work in progress), May 2013.
[I-D.templin-ipwave-uam-its]
Templin, F. L., "Urban Air Mobility Implications for
Intelligent Transportation Systems", draft-templin-ipwave-
uam-its-04 (work in progress), January 2021.
[I-D.templin-ironbis]
Templin, F. L., "The Interior Routing Overlay Network
(IRON)", draft-templin-ironbis-16 (work in progress),
March 2014.
[I-D.templin-v6ops-pdhost]
Templin, F. L., "IPv6 Prefix Delegation and Multi-
Addressing Models", draft-templin-v6ops-pdhost-27 (work in
progress), January 2021.
[OVPN] OpenVPN, O., "http://openvpn.net", October 2016.
[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>.
[RFC2003] Perkins, C., "IP Encapsulation within IP", RFC 2003,
DOI 10.17487/RFC2003, October 1996,
<https://www.rfc-editor.org/info/rfc2003>.
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[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>.
[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>.
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[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, DOI 10.17487/RFC4291, February
2006, <https://www.rfc-editor.org/info/rfc4291>.
[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>.
[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>.
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[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>.
[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>.
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[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>.
[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>.
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[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.
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
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.
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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.
If the Client's underlying 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 Bridges in the communications path. Direct
interfaces must be tested periodically for reachability, e.g., via
NUD.
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A.4. AERO Critical Infrastructure Considerations
AERO Bridges can be either Commercial off-the Shelf (COTS) standard
IP routers or virtual machines in the cloud. Bridges must be
provisioned, supported and managed by the INET administrative
authority, and connected to the Bridges of other INETs via inter-
domain peerings. Cost for purchasing, configuring and managing
Bridges 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 underlying interface connected to the ANET and a
second interface connected to an INET. As with INET Proxy/Servers,
the only requirements are that they can run the AERO/OMNI code and
have at least one interface connection to the INET. ANET Proxy/
Servers must be provisioned, supported and managed by the ANET
administrative authority. Cost for purchasing, configuring and
managing Proxys is nominal, and borne by the ANET administrative
authority.
AERO Relays are simply Proxy/Servers connected to INETs and/or EUNs
that provide forwarding services for non-MNP destinations. The Relay
connects to the OMNI link and engages in eBGP peering with one or
more Bridges 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
ROS/ROR 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.
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If a Proxy/Server fails, ongoing packet forwarding to Clients will
continue by virtue of the neighbor cache entries that have already
been established in route optimization sources (ROSs). 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.
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:
o 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.
o 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.
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o 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.
o When a client resolves the domainname "amazon.com", the DNS always
returns a list of 3 A records and no AAAA records. As with
"yahoo.com", the same three A records are returned from any
worldwide Internet connection point in randomized order.
The above example strategies show differing approaches to Internet
resilience and service distribution offered by major Internet
services. The Google approach exposes only a single IPv4 and a
single IPv6 address to clients. Clients can then select whichever IP
protocol version offers the best response, but will always use the
same IP address according to the current Internet connection point.
This means that the IP address offered by the network must lead to a
highly-available server and/or service distribution point. In other
words, resilience is predicated on high availability within the
network and with no client-initiated failovers expected (i.e., it is
all-or-nothing from the client's perspective). However, Google does
provide for worldwide distributed service distribution by virtue of
the fact that each Internet connection point responds with a
different IPv6 and IPv4 address. The IETF approach is like google
(all-or-nothing from the client's perspective), but provides only a
single IPv4 or IPv6 address on a worldwide basis. This means that
the addresses must be made highly-available at the network level with
no client failover possibility, and if there is any worldwide service
distribution it would need to be conducted by a network element that
is reached via the IP address acting as a service distribution point.
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
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or more AERO Proxy/Server addresses through the mechanisms discussed
in earlier sections. Each Proxy/Server address presumably leads to a
fault-tolerant clustering arrangement such as supported by Linux-HA,
Extended Virtual Synchrony or Paxos. Such an arrangement has
precedence in common Internet service deployments in lightweight
virtual machines without requiring expensive hardware deployment.
Similarly, common Internet service deployments set service IP
addresses on service distribution points that may relay requests to
many different servers.
For AERO, the expectation is that a combination of the Google/IETF
and Yahoo/Amazon philosophies would be employed. The AERO Client
connects to different ANET access points and can receive 1-2 Proxy/
Server ADM-LLAs 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 to draft-templin-6man-aero-33:
o New baseline version with corrections and section reorganizations
to improve document flow.
Author's Address
Fred L. Templin (editor)
Boeing Research & Technology
P.O. Box 3707
Seattle, WA 98124
USA
Email: fltemplin@acm.org
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