Network Working Group F. Templin, Ed.
Internet-Draft Boeing Research & Technology
Obsoletes: rfc5320, rfc5558, rfc5720, March 17, 2021
rfc6179, rfc6706 (if
approved)
Intended status: Standards Track
Expires: September 18, 2021
Automatic Extended Route Optimization (AERO)
draft-templin-intarea-6706bis-95
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 (ND) protocol
and links ND to IP forwarding. Prefix delegation/registration
services are employed for network admission and to manage the routing
system. Multilink operation, mobility management, multicast, quality
of service (QoS) signaling 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 Virtual
Private Networks (VPNs) and many other applications.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 18, 2021.
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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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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Automatic Extended Route Optimization (AERO) . . . . . . . . 11
3.1. AERO Node Types . . . . . . . . . . . . . . . . . . . . . 12
3.2. The AERO Service over OMNI Links . . . . . . . . . . . . 13
3.2.1. AERO/OMNI Reference Model . . . . . . . . . . . . . . 13
3.2.2. Addressing and Node Identification . . . . . . . . . 15
3.2.3. AERO Routing System . . . . . . . . . . . . . . . . . 16
3.2.4. OMNI Link Segment Routing . . . . . . . . . . . . . . 18
3.2.5. Segment Routing Topologies (SRTs) . . . . . . . . . . 22
3.2.6. Segment Routing For OMNI Link Selection . . . . . . . 23
3.2.7. Segment Routing Within the OMNI Link . . . . . . . . 23
3.3. OMNI Interface Characteristics . . . . . . . . . . . . . 24
3.4. OMNI Interface Initialization . . . . . . . . . . . . . . 26
3.4.1. AERO Server/Relay Behavior . . . . . . . . . . . . . 26
3.4.2. AERO Proxy Behavior . . . . . . . . . . . . . . . . . 26
3.4.3. AERO Client Behavior . . . . . . . . . . . . . . . . 27
3.4.4. AERO Bridge Behavior . . . . . . . . . . . . . . . . 27
3.5. OMNI Interface Neighbor Cache Maintenance . . . . . . . . 27
3.5.1. OMNI Neighbor Interface Attributes . . . . . . . . . 29
3.5.2. OMNI Neighbor Advertisement Message Flags . . . . . . 29
3.6. OMNI Interface Encapsulation and Re-encapsulation . . . . 30
3.7. OMNI Interface Decapsulation . . . . . . . . . . . . . . 30
3.8. OMNI Interface Data Origin Authentication . . . . . . . . 31
3.9. OMNI Interface MTU . . . . . . . . . . . . . . . . . . . 31
3.10. OMNI Interface Forwarding Algorithm . . . . . . . . . . . 32
3.10.1. Client Forwarding Algorithm . . . . . . . . . . . . 33
3.10.2. Proxy/Server Forwarding Algorithm . . . . . . . . . 34
3.10.3. Bridge Forwarding Algorithm . . . . . . . . . . . . 36
3.11. OMNI Interface Error Handling . . . . . . . . . . . . . . 37
3.12. AERO Router Discovery, Prefix Delegation and
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Autoconfiguration . . . . . . . . . . . . . . . . . . . . 39
3.12.1. AERO Service Model . . . . . . . . . . . . . . . . . 40
3.12.2. AERO Client Behavior . . . . . . . . . . . . . . . . 40
3.12.3. AERO Server Behavior . . . . . . . . . . . . . . . . 42
3.13. The AERO Proxy . . . . . . . . . . . . . . . . . . . . . 45
3.13.1. Combined Proxy/Servers . . . . . . . . . . . . . . . 48
3.13.2. Detecting and Responding to Server Failures . . . . 48
3.13.3. Point-to-Multipoint Server Coordination . . . . . . 49
3.14. AERO Address Resolution . . . . . . . . . . . . . . . . . 49
3.14.1. Route Optimization Initiation . . . . . . . . . . . 50
3.14.2. Relaying the NS(AR) *NET Packet(s) . . . . . . . . . 51
3.14.3. Processing the NS(AR) and Sending the NA(AR) . . . . 51
3.14.4. Relaying the NA(AR) . . . . . . . . . . . . . . . . 52
3.14.5. Processing the NA(AR) . . . . . . . . . . . . . . . 52
3.14.6. Route Optimization Maintenance . . . . . . . . . . . 53
3.15. Neighbor Unreachability Detection (NUD) . . . . . . . . . 54
3.16. Mobility Management and Quality of Service (QoS) . . . . 55
3.16.1. Mobility Update Messaging . . . . . . . . . . . . . 56
3.16.2. Announcing Link-Layer Address and/or QoS Preference
Changes . . . . . . . . . . . . . . . . . . . . . . 57
3.16.3. Bringing New Links Into Service . . . . . . . . . . 57
3.16.4. Deactivating Existing Links . . . . . . . . . . . . 57
3.16.5. Moving Between Servers . . . . . . . . . . . . . . . 58
3.17. Multicast . . . . . . . . . . . . . . . . . . . . . . . . 59
3.17.1. Source-Specific Multicast (SSM) . . . . . . . . . . 59
3.17.2. Any-Source Multicast (ASM) . . . . . . . . . . . . . 61
3.17.3. Bi-Directional PIM (BIDIR-PIM) . . . . . . . . . . . 62
3.18. Operation over Multiple OMNI Links . . . . . . . . . . . 62
3.19. DNS Considerations . . . . . . . . . . . . . . . . . . . 63
3.20. Transition Considerations . . . . . . . . . . . . . . . . 63
3.21. Detecting and Reacting to Server and Bridge Failures . . 64
3.22. AERO Clients on the Open Internet . . . . . . . . . . . . 64
3.23. Time-Varying MNPs . . . . . . . . . . . . . . . . . . . . 68
4. Implementation Status . . . . . . . . . . . . . . . . . . . . 68
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 68
6. Security Considerations . . . . . . . . . . . . . . . . . . . 69
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 71
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 72
8.1. Normative References . . . . . . . . . . . . . . . . . . 72
8.2. Informative References . . . . . . . . . . . . . . . . . 74
Appendix A. Non-Normative Considerations . . . . . . . . . . . . 80
A.1. Implementation Strategies for Route Optimization . . . . 80
A.2. Implicit Mobility Management . . . . . . . . . . . . . . 81
A.3. Direct Underlying Interfaces . . . . . . . . . . . . . . 81
A.4. AERO Critical Infrastructure Considerations . . . . . . . 81
A.5. AERO Server Failure Implications . . . . . . . . . . . . 82
A.6. AERO Client / Server Architecture . . . . . . . . . . . . 83
Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 85
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Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 86
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 such as intelligent transportation
systems. AERO is an internetworking and mobility management service
that employs the Overlay Multilink Network Interface (OMNI)
[I-D.templin-6man-omni-interface] 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 IP packets as single-hop neighbors via
encapsulation. The OMNI Adaptation Layer (OAL) supports multilink
operation for increased reliability, bandwidth optimization and
traffic path selection while accommodating Maximum Transmission Unit
(MTU) diversity.
The AERO service comprises Clients, Proxys, Servers and Relays that
are seen as OMNI link neighbors as well as Bridges that interconnect
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 (ND) protocol
[RFC4861] and links ND to IP forwarding. 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
QoS fluctuations, and link-layer address changes are signaled by ND
messaging the same as for any IPv6 link.
AERO provides a cloud-based service where mobile node Clients may use
any Server acting as a Mobility Anchor Point (MAP) and fixed nodes
may use any Relay on the link for efficient communications. Fixed
nodes forward packets destined to other AERO nodes via the nearest
Relay, which forwards them through the cloud. A mobile node's
initial packets are forwarded through the Server, while direct
routing is supported through automatic extended route optimization
while data packets are flowing. Both unicast and multicast
communications are supported, and mobile nodes may efficiently move
between locations while maintaining continuous communications with
correspondents and without changing their IP Address.
AERO Bridges are interconnected in a secured private BGP overlay
routing instance to provide an OAL routing/bridging service that
joins the underlying Internetworks of multiple disjoint
administrative domains into a single unified OMNI link at a layer
below IP. Each OMNI link instance is characterized by the set of
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Mobility Service Prefixes (MSPs) common to all mobile nodes. The
link extends to the point where a Relay/Server is on the optimal
route from any correspondent node on the link, and provides a conduit
between the underlying Internetwork and the OMNI link. To the
underlying Internetwork, the Relay/Server is the source of a route to
the MSP, and hence uplink traffic to the mobile node is naturally
routed to the nearest Relay/Server.
AERO can be used with OMNI links that span private-use Internetworks
and/or public Internetworks such as the global Internet. In the
latter case, some end systems may be located behind global Internet
Network Address Translators (NATs). A means for robust traversal of
NATs while avoiding "triangle routing" is therefore provided.
AERO assumes the use of PIM Sparse Mode in support of multicast
communication. In support of Source Specific Multicast (SSM) when a
Mobile Node is the source, AERO route optimization ensures that a
shortest-path multicast tree is established with provisions for
mobility and multilink operation. In all other multicast scenarios
there are no AERO dependencies.
AERO was designed for aeronautical networking 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 using tunneling software such as
OpenVPN [OVPN] 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.
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-interface] is used extensively throughout.
The following terms are defined within the scope of this document:
IPv6 Neighbor Discovery (ND)
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an IPv6 control message service for coordinating neighbor
relationships between nodes connected to a common link. AERO uses
the ND service specified in [RFC4861].
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 ND messaging) are also in scope. Most
notably, 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 IPv6 source address of an 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 connected IP network topology with a coherent routing and
addressing plan and that provides a transit backbone service for
ANET end systems. INETs also provide an underlay service over
which the 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. Each
partition is fully connected internally but disconnected from
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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 below.)
*NET address
an IP address assigned to a node's interface connection to a *NET.
*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.
OMNI link
the same as defined in [I-D.templin-6man-omni-interface], and
manifested by IPv6 encapsulation [RFC2473]. The OMNI link spans
underlying INET segments joined by virtual bridges in a spanning
tree the same as a bridged campus LAN. AERO nodes on the OMNI
link appear as single-hop neighbors even though they may be
separated by multiple underlying INET hops, and can use Segment
Routing [RFC8402] to cause packets to visit selected waypoints on
the link.
OMNI Interface
a node's attachment to an OMNI link. Since the addresses assigned
to an OMNI interface 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 process whereby original IP packets admitted
into the interface are wrapped in a mid-layer IPv6 header and
subject to fragmentation and reassembly. The OAL is also
responsible for generating MTU-related control messages as
necessary, and for providing addressing context for spanning
multiple segments of a bridged OMNI link.
original (or, "inner") 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 OAL headers and trailers
before OAL fragmentation, or following OAL reassembly.
OAL fragment
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a portion of an OAL packet following fragmentation but prior to
*NET encapsulation, or following *NET encapsulation but prior to
OAL reassembly.
*NET packet
an OAL fragment following *NET encapsulation or prior to *NET
decapsulation. OAL sources and destinations exchange *NET packets
over underlying interfaces, and may be separated by one or more
OAL intermediate nodes.
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.
OAL destination
an OMNI interface acts as an OAL destination when it decapsulates
*NET packets, then performs OAL reassembly and decapsulation to
derive 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-interface]). 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-interface].
Mobile Network Prefix Unique Local Address (MNP-ULA)
an IPv6 Unique-Local Address derived from an MNP-LLA.
Administrative Link Local Address (ADM-LLA)
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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-interface].
Administrative Unique Local Address (ADM-ULA)
an IPv6 Unique-Local Address derived from an ADM-LLA.
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
Servers. The Client assigns an MNP-LLA to the OMNI interface for
use in ND exchanges with other AERO nodes and forwards packets to
correspondents according to OMNI interface neighbor cache state.
AERO Server ("Server")
an INET node that configures an OMNI interface to provide default
forwarding and Mobility Anchor Point (MAP) services for AERO
Clients. The Server assigns an ADM-LLA to its OMNI interface to
support the operation of the ND services, and advertises all of
its associated MNPs via BGP peerings with Bridges.
AERO Relay ("Relay")
an AERO Server that also provides forwarding services between
nodes reached via the OMNI link and correspondents on other links.
AERO Relays are provisioned with MNPs (i.e., the same as for an
AERO Client) and run a dynamic routing protocol to discover any
non-MNP IP GUA routes in service on its connected INET links. In
both cases, the Relay advertises the MSP(s) to its downstream
networks, and distributes all of its associated MNPs and non-MNP
IP GUA routes via BGP peerings with Bridges (i.e., the same as for
an AERO Server).
AERO Bridge ("Bridge")
a node that provides hybrid routing/bridging services (as well as
a security trust anchor) for nodes on an OMNI link. The Bridge
forwards packets between OMNI link segments at the OAL layer
without decrementing the network layer IP TTL/Hop Limit. AERO
Bridges peer with Servers and other Bridges to discover the full
set of MNPs for the link as well as any non-MNP IP GUA routes that
are reachable via Relays.
AERO Proxy ("Proxy")
a node that provides proxying services between Clients in an ANET
and Servers in external INETs. The AERO Proxy is a conduit
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between the ANET and external INETs in the same manner as for
common web proxys, and behaves in a similar fashion as for ND
proxys [RFC4389]. A node may be configured to act as either a
Proxy and/or a Server, depending on Client Server selection
criteria.
ingress tunnel endpoint (ITE)
an OMNI interface endpoint that injects encapsulated packets into
an OMNI link.
egress tunnel endpoint (ETE)
an OMNI interface endpoint that receives encapsulated packets from
an OMNI link.
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.
network layer address
the source or destination address of an encapsulated 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 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 Server or Proxy acting on behalf
of the source Client, or may be the Client itself if the Client is
connected to the INET either directly or through a NAT.
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Route Optimization responder (ROR)
the AERO node nearest the target destination that responds to
route optimization requests. The ROR may be a Proxy/Server acting
on behalf of a target MNP Client, a Relay for a non-MNP
destination or may be the target Client itself.
MAP List
a geographically and/or topologically referenced list of addresses
of all Servers within the same OMNI link. There is a single MAP
list for the entire OMNI link.
Distributed Mobility Management (DMM)
a BGP-based overlay routing service coordinated by Servers and
Bridges that tracks all Server-to-Client associations.
Mobility Service (MS)
the collective set of all Servers, Proxys, Bridges and Relays that
provide the AERO Service to Clients.
Mobility Service Endpoint MSE)
an individual Server, Proxy, Bridge or Relay in the Mobility
Service.
Throughout the document, the simple terms "Client", "Server",
"Bridge", "Proxy" and "Relay" refer to "AERO Client", "AERO Server",
"AERO Bridge", "AERO Proxy" 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 DHCPv6 [RFC8415] and IPv6 ND [RFC4861] (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 are Mobile Nodes (MNs) that configure OMNI interfaces
over underlying interfaces with addresses that may change when the
Client moves to a new network connection point. AERO Clients
register their Mobile Network Prefixes (MNPs) with the AERO service,
and distribute the MNPs to nodes on EUNs. AERO Bridges, Servers,
Proxys 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 provide hybrid routing/bridging services (as well as a
security trust anchor) for nodes on an OMNI link. Bridges use
standard IPv6 routing to forward packets both within the same *NET
partition and between disjoint *NET partitions based on an IPv6
encapsulation mid-layer known as the OMNI Adaptation Layer (OAL)
[I-D.templin-6man-omni-interface]. During forwarding, the inner IP
layer experiences a virtual bridging service since the inner IP TTL/
Hop Limit is not decremented. Each Bridge also peers with 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 present the OMNI link as a set of
one or more Mobility Service Prefixes (MSPs) and configure secured
tunnels with Servers, Relays, Proxys and other Bridges; they further
maintain IP forwarding table entries for each MNP and any other
reachable non-MNP prefixes.
AERO Servers in distributed INET locations provide default forwarding
and mobility/multilink services for AERO Client Mobile Nodes (MNs).
Each Server also peers with Bridges in a dynamic routing protocol
instance to advertise its list of associated MNPs (see
Section 3.2.3). Servers facilitate prefix delegation/registration
exchanges with Clients, where each delegated prefix becomes an MNP
taken from an MSP. Servers forward packets between OMNI interface
neighbors and track each Client's mobility profiles. Servers may
further act as Servers for some sets of Clients and as Proxys for
others.
AERO Proxys provide a conduit for ANET Clients to associate with
Servers in external INETs. Client and Servers exchange control plane
messages via the Proxy acting as a bridge between the ANET/INET
boundary. The Proxy forwards data packets between Clients and the
OMNI link according to forwarding information in the neighbor cache.
The Proxy function is specified in Section 3.13. Proxys may further
act as Proxys for some sets of Clients and as Servers for others.
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AERO Relays are Servers that provide forwarding services between the
OMNI interface and INET/EUN interfaces. Relays are provisioned with
MNPs the same as for an AERO Client, and also run a dynamic routing
protocol to discover any non-MNP IP routes. The Relay advertises the
MSP(s) to its connected networks, and distributes all of its
associated MNPs and non-MNP IP GUA routes via BGP peerings with
Bridges
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 |
+-+---------+--+-+
+--------------+ | Secured | | +--------------+
|AERO Server S1| | tunnels | | |AERO Server S2|
| Nbr: C1, B1 +-----+ | +-----+ Nbr: C2, B1 |
| default->B1 | | | default->B1 |
| X1->C1 | | | X2->C2 |
+-------+------+ | +------+-------+
| OMNI link | |
X===+===+===================+==)===============+===+===X
| | | |
+-----+--------+ +--------+--+-----+ +--------+-----+
|AERO Client C1| | AERO Proxy P1 | |AERO Client C2|
| Nbr: S1 | |(Proxy Nbr Cache)| | Nbr: S2 |
| default->S1 | +--------+--------+ | default->S2 |
| MNP X1 | | | MNP X2 |
+------+-------+ .--------+------. +-----+--------+
| (- Proxyed Clients -) |
.-. `---------------' .-.
,-( _)-. ,-( _)-.
.-(_ IP )-. +-------+ +-------+ .-(_ IP )-.
(__ EUN )--|Host H1| |Host H2|--(__ EUN )
`-(______)-' +-------+ +-------+ `-(______)-'
Figure 1: AERO/OMNI Reference Model
In this model:
o the OMNI link is an overlay network service configured over one or
more underlying *NET partitions which may be managed by different
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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 Servers (S1, S2).
Bridges connect the disjoint segments of a partitioned OMNI link.
o AERO Servers/Relays S1 and S2 configure secured tunnels with
Bridge B1 and also provide mobility, multilink and default router
services for their associated Clients C1 and C2.
o AERO Clients C1 and C2 associate with Servers S1 and S2,
respectively. They receive Mobile Network Prefix (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.
o AERO Proxy P1 configures a secured tunnel with Bridge B1 and
provides proxy services for AERO Clients in secured enclaves that
cannot associate directly with other OMNI link neighbors.
An OMNI link configured over a single *NET appears as a single
unified link with a consistent underlying network addressing plan.
In that case, all nodes on the link can exchange packets via simple
*NET encapsulation, since the underlying *NET is connected. In
common practice, however, an OMNI link may be partitioned into
multiple "segments", where each segment is a distinct *NET
potentially managed under a different administrative authority (e.g.,
as for worldwide aviation service providers such as ARINC, SITA,
Inmarsat, etc.). Individual *NETs may also themselves be partitioned
internally, in which case each internal partition is seen as a
separate segment.
The addressing plan of each 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 in many cases disjoint segments may not even have any
common physical link connections. Therefore, nodes can only be
assured of exchanging 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.
The same as for traditional campus LANs, multiple OMNI link segments
can be joined into a single unified link via a virtual bridging
service using the OMNI Adaptation Layer (OAL)
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[I-D.templin-6man-omni-interface] which inserts a mid-layer IPv6
encapsulation header that supports inter-segment forwarding (i.e.,
bridging) without decrementing the network-layer TTL/Hop Limit. This
bridging of OMNI link segments is shown in Figure 2:
. . . . . . . . . . . . . . . . . . . . . . .
. .
. .-(::::::::) .
. .-(::::::::::::)-. +-+ .
. (:::: Segment A :::)--|B|---+ .
. `-(::::::::::::)-' +-+ | .
. `-(::::::)-' | .
. | .
. .-(::::::::) | .
. .-(::::::::::::)-. +-+ | .
. (:::: Segment B :::)--|B|---+ .
. `-(::::::::::::)-' +-+ | .
. `-(::::::)-' | .
. | .
. .-(::::::::) | .
. .-(::::::::::::)-. +-+ | .
. (:::: Segment C :::)--|B|---+ .
. `-(::::::::::::)-' +-+ | .
. `-(::::::)-' | .
. | .
. ..(etc).. x .
. .
. .
. <- OMNI link Bridged by encapsulation -> .
. . . . . . . . . . . . . .. . . . . . . . .
Figure 2: Bridging OMNI Link Segments
Bridges, Servers, Relays and Proxys connect via secured INET tunnels
over their respective segments in a spanning tree topology rooted at
the Bridges. The secured spanning tree supports strong
authentication for IPv6 ND control messages and may also be used to
convey the initial data packets in a flow. Route optimization can
then be employed to cause data packets to take more direct paths
between OMNI link neighbors without having to strictly follow the
spanning tree.
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
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LLAs constructed from administrative identification values ("ADM-
LLAs") as specified in [I-D.templin-6man-omni-interface].
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-interface] to support OAL addressing. AERO
Clients also use Temporary ULAs constructed per
[I-D.templin-6man-omni-interface], where the addresses are typically
used only in initial control message exchanges until a stable MNP-
LLA/ULA is assigned.
AERO MSPs and MNPs are typically based on Global Unicast Addresses
(GUAs), but in some cases may be based on private-use addresses. See
[I-D.templin-6man-omni-interface] for a full specification of LLAs,
ULAs and GUAs used by AERO nodes on OMNI links.
Finally, AERO Clients and Servers configure node identification
values as specified in [I-D.templin-6man-omni-interface].
3.2.3. AERO Routing System
The AERO routing system comprises a private instance of the Border
Gateway Protocol (BGP) [RFC4271] that is coordinated between Bridges
and Servers and does not interact with either the public Internet BGP
routing system or any underlying INET routing systems.
In a reference deployment, each 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 Server further uses eBGP to peer with one or more
Bridges but does not peer with other Servers. Each *NET of a multi-
segment OMNI link must include one or more Bridges, which peer with
the Servers and Proxys within that *NET. All Bridges within the same
*NET are members of the same hub AS, and use iBGP to maintain a
consistent view of all active MNPs currently in service. The Bridges
of different *NETs peer with one another using eBGP.
Bridges advertise the OMNI link's MSPs and any non-MNP routes to each
of their Servers. This means that any aggregated non-MNPs (including
"default") are advertised to all Servers. Each Bridge configures a
black-hole route for each of its MSPs. By black-holing the MSPs, the
Bridge will maintain forwarding table entries only for the MNPs that
are currently active, and packets destined to all other MNPs will
correctly incur Destination Unreachable messages due to the black-
hole route. In this way, Servers have only partial topology
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knowledge (i.e., they know only about the MNPs of their directly
associated Clients) and they forward all other packets to Bridges
which have full topology knowledge.
Each OMNI link segment assigns a unique ADM-ULA sub-prefix of
[ULA*]::/96. 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 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 segments into a unified OMNI link over
multiple diverse administrative domains. They support a bridging
function 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 are as follows:
A: [ULA*]::1000/116->local, [ULA*]::2000/116->B, [ULA*]::3000/116->C
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 are permanent and never change, since
they correspond to fixed infrastructure elements in their respective
segments.
MNP ULAs are instead dynamically advertised in the AERO routing
system by Servers and Relays that provide service for their
corresponding MNPs. For example, if three 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
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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. OMNI Link Segment Routing
With the Client and partition prefixes in place in Bridge forwarding
tables, the OMNI interface sends control and data packets toward AERO
destination nodes located in different OMNI link segments over the
spanning tree. The OMNI interface uses the OMNI Adaptation Layer
(OAL) encapsulation service [I-D.templin-6man-omni-interface], and
includes an OMNI Routing Header (ORH) as an extension to the OAL
header if final segment forwarding information is available, e.g., in
the neighbor cache. (For nodes located in the same OMNI link
segment, or when no final segment forwarding information is
available, the ORH may be omitted.) The ORH is formatted as shown in
Figure 3:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Hdr Ext Len | Routing Type | SRT | FMT |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Last Hop Segment-id (LHS) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Link Layer Address (L2ADDR) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Destination Suffix (if necessary) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Null Padding (if necessary) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: OMNI Routing Header (ORH) Format
In this format:
o Next Header identifies the type of header immediately following
the ORH.
o Hdr Ext Len is the length of the Routing header in 8-octet units
(not including the first 8 octets), with trailing padding added if
necessary to produce an integral number of 8-octet units.
o Routing Type is set to TBD1 (see IANA Considerations).
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o Segments Left is omitted, and replaced by a 5-bit SRT and 3-bit
FMT field.
o SRT - a 5-bit Segment Routing Topology prefix length value that
(when added to 96) determines the prefix length to apply to the
ADM-ULA formed from concatenating [ULA*]::/96 with the 32 bit LHS
value that follows (for example, the value 16 corresponds to the
prefix length 112).
o FMT - a 3-bit "Framework/Mode/Type" code corresponding to the
included Link Layer Address as follows:
* When the most significant bit (i.e., "Framework") is set to 1,
L2ADDR is the *NET encapsulation address for the target Client
itself; otherwise L2ADDR is the address of the Server/Proxy
named in the LHS.
* When the next most significant bit (i.e., "Mode") is set to 1,
the Framework node is (likely) located behind a *NET Network
Address Translator (NAT); otherwise, it is on the open *NET.
* When the least significant bit (i.e., "Type") is set to 0,
L2ADDR includes a UDP Port Number followed by an IPv4 address;
otherwise, it includes a UDP Port Number followed by an IPv6
address.
o LHS - the 32 bit ID of a node in the Last Hop Segment that
services the target. When SRT and LHS are both set to 0, the LHS
is considered unspecified. When SRT is set to 0 and LHS is non-
zero, the prefix length is set to 128. SRT and LHS provide
guidance to the OMNI interface forwarding algorithm.
Specifically, if SRT/LHS is located in the local OMNI link
segment, the OAL source can omit the ORH and (following any
necessary NAT traversal messaging) send directly to the OAL
destination according to FMT/L2ADDR. Otherwise, it includes the
ORH and forwards according to the OMNI link spanning tree.
o Link Layer Address (L2ADDR) - Formatted according to FMT, and
identifies the link-layer address (i.e., the encapsulation
address) of the target. The UDP Port Number appears in the first
two octets and the IP address appears in the next 4 octets for
IPv4 or 16 octets for IPv6. The Port Number and IP address are
recorded in network byte order, and in ones-compliment
"obfuscated" form per [RFC4380]. The OMNI interface forwarding
algorithm uses FMT/L2ADDR to determine the *NET encapsulation
address for local forwarding when SRT/LHS is located in the same
OMNI link segment. Note that if the target is behind a NAT,
L2ADDR will contain the mapped *NET address stored in the NAT;
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otherwise, L2ADDR will contain the native *NET information of the
target itself.
o Destination Suffix is a 64-bit field included only for OAL non-
first-fragments. Present only when Hdr Ext Len indicates that at
least 8 bytes follow L2ADDR. When present, encodes the 64-bit
MNP-ULA suffix for the target Client.
o Null Padding contains zero-valued octets as necessary to pad the
ORH to an integral number of 8-octet units.
AERO neighbors use OAL encapsulation and fragmentation to exchange
OAL packets as specified in [I-D.templin-6man-omni-interface]. When
an AERO node's OMNI interface (acting as an OAL source) uses OAL
encapsulation for an original IP packet with source address
2001:db8:1:2::1 and destination address 2001:db8:1234:5678::1, it
sets the OAL header source address to its own ULA (e.g.,
[ULA*]::2001:db8:1:2), sets the destination address to the MNP-ULA
corresponding to the IP destination address (e.g.,
[ULA*]::2001:db8:1234:5678), selects an Identification and appends an
OAL checksum.
If the neighbor cache information indicates that the target is in a
different segment, the OAL source next inserts an ORH immediately
following the OAL header while including the correct SRT, FMT, LHS,
L2ADDR and Destination Suffix if fragmentation if needed (in this
case, the Destination Suffix is 2001:db8:1234:5678). Next, the OAL
source overwrites the OAL header destination address with the LHS
Subnet Router Anycast address (for example, for LHS 3000:4567 with
SRT 16, the Subnet Router Anycast address is [ULA*]::3000:0000).
(Note: if the ADM-ULA of the last-hop Proxy/Server is known but the
SRT, FMT, LHS and L2ADDR are not (yet) known, the OAL source instead
overwrites the OAL header destination address with the ADM-ULA.)
The OAL source then fragments the OAL packet, with each resulting OAL
fragment including the OAL/ORH headers while only the first fragment
includes the original IPv6 header. (Note that the packet is prepared
as an "atomic fragment" even if no actual fragmentation was
required.) The OAL source finally encapsulates each resulting OAL
fragment in an *NET header to form a *NET packet, with source address
set to its own *NET address (e.g., 192.0.2.100) and destination set
to the *NET address of a Bridge (e.g., 192.0.2.1).
The *NET packet encapsulation format in the above example is shown in
Figure 4:
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| *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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ORH (if necessary)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OAL Fragment Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Inner IP Header |
| (first-fragment only) )
| src = 2001:db8:1:2::1 |
| dst = 2001:db8:1234:5678::1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ ~
~ Inner Packet Body/Fragment ~
~ ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: *NET Packet
In this format, the inner IP header and packet body/fragment are from
the original IP packet, the OAL header is an IPv6 header prepared
according to [RFC2473], the ORH is a Routing Header extension of the
OAL header the Fragment Header identifies each fragment, and the INET
header is prepared as discussed in Section 3.6. When the OAL source
transmits the resulting *NET packets, they are forwarded over
possibly multiple OMNI link spanning tree hops until they arrive at
the OAL destination.
This gives rise to a routing system that contains both Client MNP-ULA
routes that may change dynamically due to regional node mobility and
per-partition ADM-ULA routes that rarely if ever change. The Bridges
can therefore provide link-layer bridging by sending packets over the
spanning tree instead of network-layer routing according to MNP
routes. As a result, opportunities for packet loss due to node
mobility between different segments are mitigated.
In normal operations, IPv6 ND messages are conveyed over secured
paths between OMNI link neighbors so that specific Proxys, Servers or
Relays can be addressed without being subject to mobility events.
Conversely, only the first few packets destined to Clients need to
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traverse secured paths until route optimization can determine a more
direct path.
Note: When the OAL source and destination are on the same INET
segment, the ORH is not needed and OAL header compression can be used
to significantly reduce encapsulation overhead
[I-D.templin-6man-omni-interface].
Note: When the OAL source has multiple inner IP packets to send to
the same OAL destination, it can perform "packing" to generate a
"super-packet" [I-D.templin-6man-omni-interface]. In that case, the
OAL/ORH super-packet may include up to N inner packets as long as the
total length of the super-packet does not exceed the OMNI interface
MTU.
Note: Use of an IPv6 "minimal encapsulation" format (i.e., an IPv6
variant of [RFC2004]) based on extensions to the ORH was considered
and abandoned. In the approach, the ORH would be inserted as an
extension header to the original IPv6 packet header. The IPv6
destination address would then be written into the ORH, and the ULA
corresponding to the destination would be overwritten in the IPv6
destination address. This would seemingly convey enough forwarding
information so that OAL encapsulation could be avoided. However,
this "minimal encapsulation" IPv6 packet would then have a non-ULA
source address and ULA destination address, an incorrect value in
upper layer protocol checksums, and a Hop Limit that is decremented
within the spanning tree when it should not be. The insertion and
removal of the ORH would also entail rewriting the Payload Length and
Next Header fields - again, invalidating upper layer checksums.
These irregularities would result in implementation challenges and
the potential for operational issues, e.g., since actionable ICMPv6
error reports could not be delivered to the original source. In
order to address the issues, still more information such as the
original IPv6 source address could be written into the ORH. However,
with the additional information the benefit of the "minimal
encapsulation" savings quickly diminishes, and becomes overshadowed
by the implementation and operational irregularities.
3.2.5. 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 Virtual LAN (VLAN) service for the OMNI link. In some cases (e.g.,
when redundant topologies are needed for fault tolerance and
reliability) it may be beneficial to deploy multiple SRTs that act as
independent overlay instances. A communication failure in one
instance therefore will not affect communications in other instances.
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Each SRT is identified by a distinct 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 anycast ADM-ULA
corresponding to its SRT prefix length. The anycast ADM-ULA is used
for OMNI interface determination in Safety-Based Multilink (SBM) as
discussed in [I-D.templin-6man-omni-interface]. Each OMNI interface
further applies Performance-Based Multilink (PBM) internally.
3.2.6. Segment Routing For OMNI Link Selection
An original IPv6 source can direct an IPv6 packet to an AERO node by
including a standard IPv6 Segment Routing Header (SRH) [RFC8754] with
the anycast ADM-ULA for the selected SRT as either the IPv6
destination or as an intermediate hop within the SRH. This allows
the original source to determine the specific OMNI link topology a
packet will traverse when there may be multiple alternatives.
When the AERO node processes the SRH and forwards the 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).
3.2.7. Segment Routing Within the OMNI Link
OAL sources can insert an ORH for Segment Routing within the OMNI
link to influence the paths of OAL packets sent to OAL destinations
in remote segments without requiring all packets to traverse strict
spanning tree paths.
When an AERO node's OMNI interface has an original IP packet to send
to a target discovered through route optimization located in the same
OMNI link segment, it acts as an OAL source to perform OAL
encapsulation and fragmentation. The node then uses the target's
Link Layer Address (L2ADDR) information for *NET encapsulation.
When an AERO node's OMNI interface has an original IP packet to send
to a route optimization target located in a remote OMNI link segment,
it acts as an OAL source the same as above but also includes an ORH
while setting the OAL destination to the Subnet Router Anycast
address for the final OMNI link segment, then forwards the resulting
*NET packets to a Bridge.
When a Bridge receives a *NET packet destined to its Subnet Router
Anycast address with an ORH with SRT/LHS values corresponding to the
local segment, it examines the L2ADDR according to FMT and removes
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the ORH from the packet. The Bridge then writes the MNP-ULA
corresponding to the ORH Destination Suffix into the OAL destination
address, re-encapsulates the *NET packet according to L2ADDR and
forwards the *NET packet either to the LHS Server/Proxy or directly
to the target Client itself. In this way, the Bridge participates in
route optimization to reduce traffic load and suboptimal routing
through strict spanning tree paths.
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 several NATs. Native INET interfaces have global IP addresses
that are reachable from any INET correspondent. All Server, Relay
and Bridge interfaces are native interfaces, as are INET-facing
interfaces of Proxys. NATed INET interfaces connect to a private
network behind one or more NATs that provide INET access. Clients
that are behind a NAT are required to send periodic keepalive
messages to keep NAT state alive when there are no data packets
flowing.
o ANET interfaces connect to an ANET that is separated from the open
INET by a Proxy. Proxys can actively issue control messages over
the INET on behalf of the Client to reduce ANET congestion.
o VPNed interfaces use security encapsulation over the INET to a
Virtual Private Network (VPN) server that also acts as a Server or
Proxy. 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 a Server or Proxy 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 as discussed in Section 3.2.4.
OMNI interfaces use link-layer encapsulation (see: Section 3.6) to
exchange packets with OMNI link neighbors over INET or VPNed
interfaces as well as over ANET interfaces for which the Client and
Proxy 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 Proxy are known to be on the same
underlying link.
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OMNI interfaces maintain a neighbor cache for tracking per-neighbor
state the same as for any interface. OMNI interfaces use ND messages
including Router Solicitation (RS), Router Advertisement (RA),
Neighbor Solicitation (NS) and Neighbor Advertisement (NA) for
neighbor cache management.
OMNI interfaces send ND messages with an OMNI option formatted as
specified in [I-D.templin-6man-omni-interface]. The OMNI option
includes prefix registration information and Interface Attributes
containing link information parameters for the OMNI interface's
underlying interfaces. Each OMNI option may include multiple
Interface Attributes sub-options, each identified by an ifIndex
value.
A Client's OMNI interface may be configured over multiple underlying
interface connections. For example, common mobile handheld devices
have both wireless local area network ("WLAN") and cellular wireless
links. These links are often used "one at a time" with low-cost WLAN
preferred and highly-available cellular wireless as a standby, but a
simultaneous-use capability could provide benefits. In a more
complex example, aircraft frequently have many wireless data link
types (e.g. satellite-based, cellular, terrestrial, air-to-air
directional, etc.) with diverse performance and cost properties.
If a Client's multiple underlying interfaces are used "one at a time"
(i.e., all other interfaces are in standby mode while one interface
is active), then ND message OMNI options include only a single
Interface Attributes sub-option set to constant values. In that
case, the Client would appear to have a single interface but with a
dynamically changing link-layer address.
If the Client has multiple active underlying interfaces, then from
the perspective of ND it would appear to have multiple link-layer
addresses. In that case, ND message OMNI options MAY include
multiple Interface Attributes sub-options - each with values that
correspond to a specific interface. Every ND message need not
include Interface Attributes for all underlying interfaces; for any
attributes not included, the neighbor considers the status as
unchanged.
Bridge, Server and Proxy OMNI interfaces may be configured over one
or more secured tunnel interfaces. The OMNI interface configures
both an ADM-LLA and its corresponding ADM-ULA, while the underlying
secured tunnel interfaces are either unnumbered or configure the same
ULA. The OMNI interface acting as an OAL source encapsulates and
fragments each original IP packet, then and presents the resulting
*NET packets to the underlying secured tunnel interface. Routing
protocols such as BGP that run over the OMNI interface do not employ
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OAL encapsulation, but rather present the routing protocol messages
directly to the underlying secured tunnels while using the ULA as the
source address. This distinction must be honored consistently
according to each node's configuration so that the IP forwarding
table will associate discovered IP routes with the correct interface.
3.4. OMNI Interface Initialization
AERO Servers, Proxys 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 assigned to a non-OMNI interface are
directed to the OMNI interface.
OMNI interface initialization procedures for Servers, Proxys, Clients
and Bridges are discussed in the following sections.
3.4.1. AERO Server/Relay Behavior
When a Server enables an OMNI interface, it assigns an ADM-{LLA,ULA}
appropriate for the given OMNI link segment. The Server also
configures secured tunnels with one or more neighboring Bridges and
engages in a BGP routing protocol session with each Bridge.
The OMNI interface provides a single interface abstraction to the IP
layer, but internally comprises multiple secured tunnels as well as
an NBMA nexus for sending *NET packets to OMNI interface neighbors.
The Server further configures a service to facilitate 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 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 Proxy Behavior
When a Proxy enables an OMNI interface, it assigns an ADM-{LLA, ULA}
and configures secured tunnels with neighboring Bridges the same as
for Servers. The Proxy also configures secured tunnels with one or
more neighboring Bridges and maintains per-Client neighbor cache
entries based on control message exchanges. Importantly Proxys are
often configured to act as Servers, and vice-versa.
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3.4.3. 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 with ND
parameters over its underlying interfaces to a Server, which returns
an RA message with corresponding parameters. The RS/RA messages may
pass through a Proxy in the case of a Client's ANET interface, or
through one or more NATs in the case of a Client's INET interface.
(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 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 provide an MNP.)
3.4.4. AERO Bridge Behavior
AERO Bridges configure an OMNI interface and assign the ADM-ULA
Subnet Router Anycast address for each OMNI link segment they connect
to. Bridges configure secured tunnels with Servers, Proxys and other
Bridges, and engage in a BGP routing protocol session with neighbors
on the spanning tree (see: Section 3.2.3).
3.5. OMNI Interface Neighbor Cache Maintenance
Each OMNI interface maintains a conceptual neighbor cache that
includes an entry for each neighbor it communicates with on the OMNI
link per [RFC4861]. Proxy neighbor cache entries are created and
maintained by AERO Proxys when they process Client/Server ND
exchanges, and remain in place for durations bounded by ND and prefix
lifetimes. AERO Proxys maintain proxy neighbor cache entries for
each of their associated Clients. Proxy neighbor cache entries track
the Client state and the address of the Client's associated
Server(s).
To the list of neighbor cache entry states in Section 7.3.2 of
[RFC4861], Proxy and Server OMNI interfaces add an additional state
DEPARTED that applies to Clients that have recently departed. The
interface sets a "DepartTime" variable for the neighbor cache entry
to "DEPART_TIME" seconds. DepartTime is decremented unless a new ND
message causes the state to return to REACHABLE. While a neighbor
cache entry is in the DEPARTED state, packets destined to the target
Client are forwarded to the Client's new location instead of being
dropped. When DepartTime decrements to 0, the neighbor cache entry
is deleted. It is RECOMMENDED that DEPART_TIME be set to the default
constant value REACHABLE_TIME plus 10 seconds (40 seconds by default)
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to allow a window for packets in flight to be delivered while stale
route optimization state may be present.
Servers can act as RORs on behalf of multilink and/or disadvantaged
Clients according to the Proxy Neighbor Advertisement specification
in Section 7.2.8 of [RFC4861]. (Well-connected Clients can act as an
ROR on their own behalf, and perform normal IPv6 ND operations the
same as for any node.) When a Server acting as an ROR receives an
authentic NS message used for route optimization, it searches for a
neighbor cache entry for the target Client. The ROR then returns a
solicited NA message without creating a neighbor cache entry for the
ROS, but creates or updates a target Client "Report List" entry for
the ROS and sets a "ReportTime" variable for the entry to REPORT_TIME
seconds. The ROR resets ReportTime when it receives a new authentic
NS message, and otherwise decrements ReportTime while no authentic NS
messages have been received. It is RECOMMENDED that REPORT_TIME be
set to the default constant value REACHABLE_TIME plus 10 seconds (40
seconds by default) to allow a window for route optimization to
converge before ReportTime decrements below REACHABLE_TIME.
When the ROS receives a solicited NA message response to its NS
message used for route optimization, it creates or updates a neighbor
cache entry for the target network-layer and link-layer addresses.
The ROS then (re)sets ReachableTime for the neighbor cache entry to
REACHABLE_TIME seconds and uses this value to determine whether
packets can be forwarded directly to the target, i.e., instead of via
a default route. 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 keepalives 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 DEPART_TIME, REPORT_TIME, REACHABLE_TIME,
MAX_UNICAST_SOLICIT, MAX_RTR_SOLCITATIONS and
MAX_NEIGHBOR_ADVERTISEMENT 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 Neighbor Interface Attributes
OMNI interface IPv6 ND messages include OMNI options
[I-D.templin-6man-omni-interface] with Interface Attributes that
provide Link-Layer Address and QoS Preference 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 ND
messages received from the neighbor; it is therefore not required
that each ND message contain all neighbor information.
The OMNI option Interface Attributes for each underlying interface
includes a two-part "Link-Layer Address" consisting of a simple IP
encapsulation address determined by the FMT and L2ADDR fields and an
ADM-ULA determined by the SRT and LHS fields. Underlying interfaces
are further selected based on their associated preference values
"high", "medium", "low" or "disabled".
Note: the OMNI option is distinct from any Source/Target Link-Layer
Address Options (S/TLLAOs) that may appear in an 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.
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.
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 Unsolicited NAs (both unicast and multicast).
o O: The O ("Override") flag is set to 0 for solicited proxy NAs 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 ND protocol operation, however, no role is
currently seen for assigning the same MNP-LLA to multiple Clients.
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3.6. OMNI Interface Encapsulation and Re-encapsulation
The OMNI interface admits original IP packets then (acting as an OAL
source) performs OAL encapsulation and fragmentation as specified in
Section 3.2.4[I-D.templin-6man-omni-interface]. For original IP
packets entering the OMNI interface from the network layer, the OMNI
interface copies the "TTL/Hop Limit", "Type of Service/Traffic Class"
[RFC2983], "Flow Label"[RFC6438] (for IPv6) and "Congestion
Experienced" [RFC3168] values in the original packet's IP header into
the corresponding fields in the OAL and *NET encapsulation header(s).
For *NET packets undergoing re-encapsulation, the OMNI interface
instead copies these values from the original *NET encapsulation
header into the new *NET encapsulation header, i.e., the values are
transferred between *NET encapsulation headers and *not* copied from
the encapsulated packet's network-layer header. (Note especially
that by copying the TTL/Hop Limit between encapsulation headers the
value will eventually decrement to 0 if there is a (temporary)
routing loop.)
The OAL source sets the *NET header UDP source port to a constant
value that it will use in each successive packet it sends. For
packets sent to a Server, Relay or Bridge, the OAL source sets the
UDP destination port to 8060, i.e., the IANA-registered port number
for AERO. For packets sent to a Client, the OAL source sets the UDP
destination port to the port value stored in the neighbor cache entry
for this Client. The OAL source finally includes/omits the UDP
checksum according to [RFC6935][RFC6936].
When a Proxy, Relay or Server re-encapsulates a packet received from
a Client that includes an OAL but no ORH, it inserts an ORH
immediately following the OAL header and adjusts the OAL payload
length and destination address field. The inserted ORH will be
removed by the final-hop Bridge, but its insertion and removal will
not interfere with reassembly at the final destination. For this
reason, Clients must reserve 40 bytes for a maximum-length ORH when
they perform OAL encapsulation (see: Section 3.9).
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 packet was received on. When *NET
packets containing OAL fragments arrive, the OMNI interface
reassembles as discussed in Section 3.9.
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3.8. OMNI Interface Data Origin Authentication
AERO nodes employ simple data origin authentication procedures. In
particular:
o AERO Bridges, Servers and Proxys accept encapsulated data packets
and control messages received from the (secured) spanning tree.
o AERO Proxys and Clients accept packets that originate from within
the same secured ANET.
o AERO Clients and Relays accept packets from downstream network
correspondents based on ingress filtering.
o AERO Clients, Relays and Servers verify the outer UDP/IP
encapsulation addresses according to [RFC4380].
o AERO Clients, Relays and Servers as OAL destinations accept OAL
packets/fragments with Identification values within the current
window for the OAL source.
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 Section 5 of [I-D.templin-6man-omni-interface] with MTU/
MRU both set to the constant value 9180 bytes, with minimum MPS set
to 400 bytes, and with path MPS set to a potentially larger value
depending on the underlying path.
When the network layer presents an original IP packet to the OMNI
interface, the OAL source encapsulates and fragments the packet if
necessary. When the network layer presents the OMNI interface with
multiple IP packets bound to the same OAL destination, the OAL source
can concatenate multiple IP packets together into a single OAL super-
packet as discussed in [I-D.templin-6man-omni-interface]. The OAL
source then fragments the encapsulated packet if necessary according
to the minimum/path MPS such that the OAL headers appear in each
fragment while the original IP packet header appears only in the
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first fragment. The OAL source then encapsulates each OAL fragment
in *NET headers for transmission over 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: A Client that does not (yet) have neighbor cache state for a
target may omit the ORH in packets with the understanding that a
Proxy/Server may insert an ORH on its behalf. For this reason,
Clients reserve 40 bytes for the largest possible ORH in their OAL
fragment size calculations.
Note: Although the ORH may be removed by a Bridge on the path (see:
Section 3.10.3), this does not interfere with the destination's
ability to reassemble in the event that the packet was fragmented.
This is due to the fact that the ORH is not included in the
fragmentable part; therefore, its removal does not invalidate the
offset values in any fragment headers.
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 *NET packets enter from the link layer (i.e., from an
OMNI interface neighbor). All packets entering a node's OMNI
interface first undergo data origin authentication as discussed in
Section 3.8. Those packets 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 *NET packets for
transmission over underlying interfaces. (If routing indicates that
the packet should instead be forwarded back to the network layer, the
packet is dropped to avoid looping). *NET-encapsulated OAL fragments
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 network layer 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 classifiers (e.g., DSCP value, port number, flow
specification, etc.) to select an outgoing underlying interface for
each OAL packet based on the node's own QoS preferences, and also to
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select a destination link-layer address based on the neighbor's
underlying interface with the highest preference. AERO
implementations SHOULD allow for QoS preference values to be modified
at runtime through network management.
If multiple outgoing interfaces and/or neighbor interfaces have a
preference of "high", the AERO node replicates the OAL packet and
sends one copy via each of the (outgoing / neighbor) interface pairs;
otherwise, the node sends a single copy of the OAL packet via an
interface with the highest preference. (While not strictly required,
successful delivery may be more likely when all OAL fragments of the
same OAL packet are sent over the same underlying interface.) 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, Proxys, 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 neighbor cache entry that
matches the destination. If there is a match, the Client selects one
or more "reachable" neighbor interfaces in the entry for forwarding
purposes. If there is no neighbor cache entry, the Client instead
forwards the packet toward a Server (the packet is intercepted by a
Proxy if there is a Proxy on the path). The Client (acting as an OAL
source) performs OAL encapsulation and sets the OAL destination
address to the MNP-ULA if there is a matching neighbor cache entry;
otherwise, it sets the OAL destination to the ADM-ULA of the Proxy/
Server. If the Client has multiple original IP packets to send to
the same neighbor, it can concatenate them in a single super-packet
[I-D.templin-6man-omni-interface]. The OAL source then performs
fragmentation to create OAL fragments (see: Section 3.9), appends any
*NET encapsulation, and sends the resulting *NET packets over
underlying interfaces to the neighbor acting as an OAL destination.
If the neighbor interface selected for forwarding is located on the
same OMNI link segment and not behind a NAT, the Client forwards the
*NET packets directly according to the L2ADDR information for the
neighbor. If the neighbor interface is behind a NAT on the same OMNI
link segment, the Client instead forwards the initial *NET packets to
its Server and initiates NAT traversal procedures. If the Client's
intended source underlying interface is also behind a NAT and located
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on the same OMNI link segment, it sends a "direct bubble" over the
interface per [RFC6081][RFC4380] to the L2ADDR found in the neighbor
cache in order to establish state in its own NAT by generating
traffic toward the neighbor (note that no response to the bubble is
expected).
The Client next sends an NS(NUD) message toward the MNP-ULA of the
neighbor via its Server as discussed in Section 3.15. If the Client
receives an NA(NUD) from the neighbor over the underlying interface,
it marks the neighbor interface as "trusted" and sends future
packets/fragments directly to the L2ADDR information for the neighbor
instead of indirectly via the Server. The Client must honor the
neighbor cache maintenance procedure by sending additional direct
bubbles and/or NS/NA(NUD) messages as discussed in [RFC6081][RFC4380]
in order to keep NAT state alive as long as packets are still
flowing.
When an *NET packet enters a Client's OMNI interface from the link-
layer, if the OAL destination matches one of the Client's MNPs or
LLAs the Client (acting as an OAL destination) reassembles and
decapsulates as necessary and delivers the inner packet to the
network layer. Otherwise, the Client drops the packet and MAY return
a network-layer ICMP Destination Unreachable message subject to rate
limiting (see: Section 3.11).
3.10.2. Proxy/Server Forwarding Algorithm
For IPv6 ND control messages originating from or destined to a
Client, the Proxy/Server intercepts the message and updates its
neighbor cache entry for the Client. If acting in Proxy-only mode,
it then forwards a (proxyed) copy of the control message to one or
more neighbors. (For example, the Proxy forwards a proxyed version
of a Client's NS/RS message to the neighbor, and forwards a proxyed
version of the neighbor's NA/RA reply to the Client.)
When the 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 *NET packets with OAL destination set to its own ADM-ULA.
When the Proxy/Server receives *NET packets with OAL destination set
to its own ADM-ULA, it performs OAL reassembly if necessary to obtain
the original IP packet.
The Proxy/Server next searches for a neighbor cache entry that
matches the original IP destination and proceeds as follows:
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o if the original IP destination matches a neighbor cache entry, the
Proxy/Sever uses one or more "reachable" neighbor interfaces in
the entry for packet forwarding using OAL encapsulation and
fragmentation according to the cached link-layer address
information. If the neighbor interface is in a different OMNI
link segment, the Proxy/Server forwards the resulting *NET packets
to a Bridge; otherwise, it forwards the *NET packets directly to
the neighbor. If the neighbor is behind a NAT, the Proxy/Server
instead forwards initial *NET packets via a Bridge while sending
an NS(NUD) to the neighbor. When the Proxy/Server receives the
NA(NUD), it can begin forwarding *NET packets directly to the
neighbor the same as discussed in Section 3.10.1 while sending
additional NS(NUD) messages as necessary to maintain NAT state.
Note that no direct bubbles are necessary since the Proxy/Server
is by definition not located behind a NAT.
o else, if the original IP destination matches a non-MNP route in
the IP forwarding table or an ADM-LLA assigned to the Proxy/
Server's OMNI interface, the Proxy/Server decapsulates the packet
and presents it to the network layer for local delivery or IP
forwarding.
o else, the Proxy/Server initiates address resolution as discussed
in Section 3.14, while retaining initial original IP packets in a
small queue awaiting address resolution completion.
When the Proxy/Server receives a *NET packet with OAL destination set
to a non-MNP ULA, it accepts the packet only if data origin
authentication succeeds and if there is a network layer routing table
for a GUA route that matches the non-MNP ULA. If there is no route,
the Proxy/Server drops the packet; otherwise, it reassembles and
decapsulates to obtain the original IP packet and presents it to the
network layer where it will be delivered according to standard IP
forwarding.
When the Proxy/Server receives a *NET packet with OAL destination set
to an MNP-ULA, it accepts the packet only if data origin
authentication succeeds and if there is a neighbor cache entry that
matches the OAL destination. If the neighbor cache entry state is
DEPARTED, the Proxy/Server inserts an ORH that encodes the MNP-ULA
destination suffix and changes the OAL destination address to the
ADM-ULA of the new Server, then re-encapsulates the *NET packet and
forwards it to a Bridge which will eventually deliver it to the new
Server.
If the neighbor cache state is REACHABLE, the Proxy/Server can
instead either reassemble first and then re-encapsulate/re-fragment
before forwarding to the Client or forward the raw fragments on to
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the Client which then must reassemble. In the former case, the
Proxy/Server can re-fragment to a size that better matches the link
MTU for the Client, which may be important for low-end links with
large MTUs. In the latter case, the Client may receive fragments
that are smaller than its link MTU but can still be reassembled; this
case may provide an important performance benefit to Proxy/Servers by
permitting them to avoid excessive reassembly and re-fragmentation
overhead. In either case, the Proxy/Server can return a PTB if
necessary (see: [I-D.templin-6man-omni-interface]) when it receives a
*NET packet containing an OAL first fragment.
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-interface].
3.10.3. Bridge Forwarding Algorithm
Bridges forward OAL fragments over secured tunnels the same as any
IPv6 router. When the Bridge receives an OAL fragment or an original
IP packet via a secured tunnel, it removes the outer *NET header and
searches for a forwarding table entry that matches the OAL
destination address. The Bridge then processes the packet as
follows:
o if the destination matches its ADM-ULA Subnet Router Anycast
address the Bridge processes the packet locally before forwarding.
The Bridge drops the packet if the OAL fragment does not include
an ORH; otherwise, for NA(NUD) messages the Bridge replaces the
OMNI option Interface Attributes sub-option with information for
its own interface while retaining the ifIndex value supplied by
the NA(NUD) message source. For all packet types, the Bridge next
examines the ORH FMT code. If the code indicates the destination
is a Client on the open *NET (or, a Client behind a NAT for which
NAT traversal procedures have already converged) the Bridge
removes the ORH then writes the MNP-ULA formed from the ORH
Destination Suffix into the OAL destination. The Bridge then re-
encapsulates the *NET fragment and forwards it to the ORH L2ADDR.
For all other destination cases, the Bridge instead writes the
ADM-ULA formed from the ORH SRT/LHS into the OAL destination
address and forwards the OAL/ORH encapsulated packet to the ADM-
ULA Server while invoking NAT traversal procedures the same as for
Proxys and Servers if necessary, noting that no direct bubbles are
necessary since only the target Client and not the Bridge is
behind a NAT.
o else, if the destination matches one of the Bridge's own
addresses, the Bridge submits the packet for local delivery to
support local applications such as routing protocols.
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o else, if the destination matches a forwarding table entry the
Bridge forwards the packet via a secured tunnel to the next hop.
If the destination matches an MSP without matching an MNP,
however, the Bridge instead drops the packet and returns an ICMP
Destination Unreachable message subject to rate limiting (see:
Section 3.11).
o else, the Bridge drops the packet and returns an ICMP Destination
Unreachable as above.
As for any IP router, the Bridge decrements the TTL/Hop Limit when it
forwards the packet. Therefore, when an OAL header is present only
the Hop Limit in the OAL header is decremented and not the TTL/Hop
Limit in the inner packet header. Bridges do not insert OAL/ORH
headers themselves; instead, they act as IPv6 routers and forward
packets based on the destination address found in the headers of
packets they receive.
3.11. OMNI Interface Error Handling
When an AERO node admits a packet into the OMNI interface, it may
receive link-layer or network-layer error indications.
A link-layer error indication is an ICMP error message generated by a
router in the INET 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 all link-layer IPv4
"Fragmentation Needed" and IPv6 "Packet Too Big" messages since they
only emit packets that are guaranteed to be no larger than the IP
minimum link MTU as discussed in Section 3.9.)
The ICMP header is followed by the leading portion of the 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".
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The link-layer error message format is shown in Figure 5 (where, "L2"
and "L3" refer to link-layer and network-layer, respectively):
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
| L2 IP Header of |
| error message |
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| L2 ICMP Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ---
~ ~ P
| IP and other encapsulation | a
| headers of original L3 packet | c
~ ~ k
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ e
~ ~ t
| IP header of |
| original L3 packet | i
~ ~ n
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~ e
| Upper layer headers and | r
| leading portion of body | r
| of the original L3 packet | o
~ ~ r
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ---
Figure 5: OMNI Interface Link-Layer Error Message Format
The AERO node rules for processing these link-layer error messages
are as follows:
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 encapsulated 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
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Destination Unreachable messages over multiple paths, the node
should allow future 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 encapsulated packets that it
sends to one of its neighbor 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 Server and release its association with the
old Server as specified in Section 3.16.5.
o When an AERO Server receives persistent link-layer Destination
Unreachable messages in response to encapsulated packets that it
sends to one of its neighbor Clients, the Server should mark the
underlying path as unusable and use another underlying path.
o When an AERO Server or Proxy receives link-layer Destination
Unreachable messages in response to an encapsulated 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 packet for which the network-layer
destination address is covered by an MSP, the Bridge drops the packet
if there is no more-specific routing information for the destination
and returns a network-layer Destination Unreachable message subject
to rate limiting. The Bridge writes the network-layer source address
of the original packet as the destination address and uses one of its
non link-local addresses as the source address of the message.
When an AERO node receives an encapsulated packet for which the
reassembly buffer it too small, it drops the packet and returns a
network-layer Packet Too Big (PTB) message. The node first writes
the MRU value into the PTB message MTU field, writes the network-
layer source address of the original packet as the destination
address and writes one of its non link-local addresses as the source
address.
3.12. AERO Router Discovery, Prefix Delegation and Autoconfiguration
AERO Router Discovery, Prefix Delegation and Autoconfiguration are
coordinated as discussed in the following Sections.
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3.12.1. AERO Service Model
Each AERO Server on the OMNI link is configured to facilitate Client
prefix delegation/registration requests. Each 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 Servers, e.g., via the Lightweight Directory
Access Protocol (LDAP) [RFC4511], via static configuration, etc.
Clients receive the same service regardless of the Servers they
select.
AERO Clients and Servers use ND messages to maintain neighbor cache
entries. AERO 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 Server state alive.
AERO Clients and Servers include prefix delegation and/or
registration parameters in RS/RA messages (see
[I-D.templin-6man-omni-interface]). The ND messages are exchanged
between Client and Server 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 Server (and Proxy)
accept the Client's MNP assertion, they inject the prefix into the
routing system and establish 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 specify the Client and Server behavior.
3.12.2. AERO Client Behavior
AERO Clients discover the addresses of Servers in a similar manner as
described in [RFC5214]. Discovery methods include static
configuration (e.g., from a flat-file map of Server addresses and
locations), or through an automated means such as Domain Name System
(DNS) name resolution [RFC1035]. Alternatively, the Client can
discover Server addresses through a layer 2 data link login exchange,
or through a unicast 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)
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"linkupnetworks.[domainname]" where "linkupnetworks" is a constant
text string and "[domainname]" is a DNS suffix for the OMNI link
(e.g., "example.com").
To associate with a Server, the Client acts as a requesting router to
request MNPs. The Client prepares an RS message with prefix
management parameters and includes a Nonce and Timestamp option if
the Client needs to correlate RA replies. If the Client already
knows the Server's ADM-LLA, it includes the LLA as the network-layer
destination address; otherwise, the Client includes the (link-local)
All-Routers multicast as the network-layer destination. If the
Client already knows its own MNP-LLA, it can use the MNP-LLA as the
network-layer source address and include an OMNI option with prefix
registration information. Otherwise, the Client uses the unspecified
address (::) as the network-layer source address and includes prefix
delegation parameters in the OMNI option (see:
[I-D.templin-6man-omni-interface]). The Client includes Interface
Attributes corresponding to the underlying interface over which it
will send the RS message, and MAY include additional Interface
Attributes specific to other underlying interfaces.
The Client then sends the RS message (either directly via Direct
interfaces, via a VPN for VPNed interfaces, via a Proxy for ANET
interfaces or via INET encapsulation for INET interfaces) while using
OAL encapsulation/fragmentation, then waits for an RA message reply
(see Section 3.12.3). The Client retries up to MAX_RTR_SOLICITATIONS
times until an RA is received. If the Client receives no RAs, or if
it receives an RA with Router Lifetime set to 0, the Client SHOULD
abandon this Server and try another Server. Otherwise, the Client
processes the prefix information found in the RA message.
When the Client processes an RA, it first performs OAL reassembly and
decapsulation then creates a neighbor cache entry with the Server's
ADM-LLA as the network-layer address and the Server's encapsulation
and/or link-layer addresses as the link-layer address. The Client
next records the RA Router Lifetime field value in the neighbor cache
entry as the time for which the Server has committed to maintaining
the MNP in the routing system via this underlying interface, and
caches the other RA configuration information including Cur Hop
Limit, M and O flags, Reachable Time and Retrans Timer. The Client
then autoconfigures MNP-LLAs for any delegated MNPs and assigns them
to the OMNI interface. The Client also caches any MSPs included in
Route Information Options (RIOs) [RFC4191] as MSPs to associate with
the OMNI link, and assigns the MTU value in the MTU option to the
underlying interface.
The Client then registers additional underlying interfaces with the
Server by sending RS messages via each additional interface as
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described above. The RS messages include the same parameters as for
the initial RS/RA exchange, but with destination address set to the
Server's ADM-LLA. The Client finally sub-delegates the MNPs to its
attached EUNs and/or the Client's own internal virtual interfaces as
described in [I-D.templin-v6ops-pdhost] to support the Client's
downstream attached "Internet of Things (IoT)". The Client then
sends additional RS messages over each underlying interface before
the Router Lifetime received for that interface expires.
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 QoS preferences 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, with Interface Attributes
specific to the selected underlying interface, and with any
additional Interface Attributes specific to other underlying
interfaces. When the Client receives the Server's RA response, it
has assurance that the Server has been updated with the new
information.
If the Client wishes to discontinue use of a Server it issues an RS
message over any underlying interface with an OMNI option with a
prefix release indication. When the Server processes the message, it
releases the MNP, sets the neighbor cache entry 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 Server withdraws the MNP
from the routing system.
3.12.3. AERO Server Behavior
AERO Servers act as IP routers and support a prefix delegation/
registration service for Clients. Servers arrange to add their ADM-
LLAs to a static map of Server addresses for the link and/or the DNS
resource records for the FQDN "linkupnetworks.[domainname]" before
entering service. Server addresses should be geographically and/or
topologically referenced, and made available for discovery by Clients
on the OMNI link.
When a Server receives a prospective Client's RS message on its OMNI
interface, 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, the Server performs OAL reassembly
and decapsulation, then authenticates the RS message and processes
the prefix delegation/registration parameters. The Server first
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 Server returns the MNPs, it also creates a forwarding table
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entry for the MNP-ULA corresponding to each MNP so that the MNPs are
propagated into the routing system (see: Section 3.2.3). For IPv6,
the Server creates an IPv6 forwarding table entry for each MNP. For
IPv4, the Server creates an IPv6 forwarding table entry with the
IPv4-compatibility MNP-ULA prefix corresponding to the IPv4 address.
The Server next creates a neighbor cache entry for the Client using
the base MNP-LLA as the network-layer address and with lifetime set
to no more than the smallest prefix lifetime. Next, the Server
updates the neighbor cache entry by recording the information in each
Interface Attributes sub-option in the RS OMNI option. The Server
also records the actual OAL/INET addresses in the neighbor cache
entry.
Next, the Server prepares an RA message using its ADM-LLA as the
network-layer source address and the network-layer source address of
the RS message as the network-layer destination address. The Server
sets the Router Lifetime to the time for which it will maintain both
this underlying interface individually and the neighbor cache entry
as a whole. The Server also sets Cur Hop Limit, M and O flags,
Reachable Time and Retrans Timer to values appropriate for the OMNI
link. The Server includes the MNPs, any other prefix management
parameters and an OMNI option with no Interface Attributes. The
Server then includes one or more RIOs that encode the MSPs for the
OMNI link, plus an MTU option (see Section 3.9). The Server finally
forwards the message to the Client using OAL encapsulation/
fragmentation as necessary.
After the initial RS/RA exchange, the Server maintains a
ReachableTime timer for each of the Client's underlying interfaces
individually (and for the Client's neighbor cache entry collectively)
set to expire after ReachableTime seconds. If the Client (or Proxy)
issues additional RS messages, the Server sends an RA response and
resets ReachableTime. If the Server receives an ND message with a
prefix release indication it sets the Client's neighbor cache entry
to the DEPARTED state and withdraws the MNP 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 Server marks the interface as DOWN. If ReachableTime expires
before any new RS is received on any individual underlying interface,
the Server sets the neighbor cache entry state to STALE and sets a 10
second timer. If the Server has not received a new RS or ND message
with a prefix release indication before the 10 second timer expires,
it deletes the neighbor cache entry and withdraws the MNP from the
routing system.
The Server processes any ND messages pertaining to the Client and
returns an NA/RA reply in response to solicitations. The Server may
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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. Finally, If the neighbor cache entry is in
the DEPARTED state, the Server deletes the entry after DepartTime
expires.
Note: Clients SHOULD notify former Servers of their departures, but
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). 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 Client/Server RS/RA messaging
will keep any NAT state alive (see above).
Note: All 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 Servers on the same link advertised different
values.
3.12.3.1. DHCPv6-Based Prefix Registration
When a Client is not pre-provisioned with an MNP-LLA, it will need
for the 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 Server to select additional
MNPs.) The DHCPv6 service [RFC8415] is used to support this
requirement.
When a Client needs to have the 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 Server
receives the RS message, it extracts the DHCPv6-PD message from the
OMNI option.
The 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 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.)
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When the 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 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 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: See [I-D.templin-6man-omni-interface] for an MNP delegation
alternative in which the Client can optionally avoid including a
DHCPv6 message sub-option. Namely, when the Client requests a single
MNP it can set the RS source to the unspecified address (::) and
include a Node Identification sub-option and Preflen in the OMNI
option (but with no DHCPv6 message sub-option). When the Server
receives the RS message, it forwards a self-generated DHCPv6 Solicit
message to the DHCPv6 server on behalf of the Client. When the
Server receives the DHCPv6 Reply, it prepares an RA message with an
OMNI option with Preflen information (but with no DHCPv6 message sub-
option), then places the (newly-created) MNP-LLA in the RA
destination address and returns the message to the Client.
3.13. The AERO Proxy
Clients may connect to protected-spectrum ANETs that employ physical
and/or link-layer security services to facilitate communications to
Servers in outside INETs. In that case, the ANET can employ an AERO
Proxy. The Proxy is located at the ANET/INET border and listens for
RS messages originating from or RA messages destined to ANET Clients.
The Proxy acts on these control messages as follows:
o when the Proxy receives an RS message from a new ANET Client, it
first authenticates the message then examines the network-layer
destination address. If the destination address is a Server's
ADM-LLA, the Proxy proceeds to the next step. Otherwise, if the
destination is (link-local) All-Routers multicast, the Proxy
selects a "nearby" Server that is likely to be a good candidate to
serve the Client and replaces the destination address with the
Server's ADM-LLA. Next, the Proxy creates a proxy neighbor cache
entry and caches the Client and Server link-layer addresses along
with the OMNI option information and any other identifying
information including Transaction IDs, Client Identifiers, Nonce
values, etc. The Proxy finally encapsulates the (proxyed) RS
message in an OAL header with source set to the Proxy's ADM-ULA
and destination set to the Server's ADM-ULA. The Proxy also
includes an OMNI header with an Interface Attributes option that
includes its own INET address plus a unique Port Number for this
Client, then forwards the message into the OMNI link spanning
tree. (Note: including a unique Port Number allows the Server to
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distinguish different Clients located behind the same Proxy at the
link-layer, whereas the link-layer addresses would otherwise be
indistinguishable)
o when the Server receives the RS, it authenticates the message then
creates or updates a neighbor cache entry for the Client with the
Proxy's ADM-ULA, INET address and Port Number as the link-layer
address information. The Server then sends an RA message back to
the Proxy via the spanning tree.
o when the Proxy receives the RA, it authenticates the message and
matches it with the proxy neighbor cache entry created by the RS.
The Proxy then caches the prefix information as a mapping from the
Client's MNPs to the Client's link-layer address, caches the
Server's advertised Router Lifetime and sets the neighbor cache
entry state to REACHABLE. The Proxy then optionally rewrites the
Router Lifetime and forwards the (proxyed) message to the Client.
The Proxy finally includes an MTU option (if necessary) with an
MTU to use for the underlying ANET interface.
After the initial RS/RA exchange, the Proxy forwards any Client data
packets for which there is no matching neighbor cache entry to a
Bridge using OAL encapsulation with its own ADM-ULA as the source and
the MNP-ULA corresponding to the Client as the destination. The
Proxy instead forwards any Client data 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 3.14.
While the Client is still attached to the ANET, the Proxy sends NS,
RS and/or unsolicited NA messages to update the Server's neighbor
cache entries on behalf of the Client and/or to convey QoS updates.
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 Server ceases to send solicited advertisements, the Proxy
sends unsolicited RAs on the ANET interface with destination set to
(link-local) All-Nodes multicast and with Router Lifetime set to zero
to inform Clients that the Server has failed. Although the Proxy
engages in ND exchanges on behalf of the Client, the Client can also
send ND messages on its own behalf, e.g., if it is in a better
position than the Proxy to convey QoS changes, etc. For this reason,
the Proxy marks any Client-originated solicitation messages (e.g. by
inserting a Nonce option) so that it can return the solicited
advertisement to the Client instead of processing it locally.
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If the Client becomes unreachable, the Proxy sets the neighbor cache
entry state to DEPARTED and retains the entry for DepartTime seconds.
While the state is DEPARTED, the Proxy forwards any packets destined
to the Client to a Bridge via OAL/ORH encapsulation. When DepartTime
expires, the Proxy deletes the neighbor cache entry and discards any
further packets destined to this (now forgotten) Client.
In some ANETs that employ a Proxy, the Client's MNP can be injected
into the ANET routing system. In that case, the Client can send data
messages without encapsulation so that the ANET routing system
transports the unencapsulated packets to the Proxy. This can be very
beneficial, e.g., if the Client connects to the ANET via low-end data
links such as some aviation wireless links.
If the first-hop ANET access router is on the same underlying link
and recognizes the AERO/OMNI protocol, the Client can avoid
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 Server or to (link-local) All-Routers multicast. The Client
includes an OMNI option formatted as specified in
[I-D.templin-6man-omni-interface].
The Client then sends the unencapsulated RS message, which will be
intercepted by the AERO-Aware access router. The access router then
encapsulates the RS message in an ANET header with its own address as
the source address and the address of a Proxy as the destination
address. The access router further remembers the address of the
Proxy so that it can encapsulate future data packets from the Client
via the same Proxy. If the access router needs to change to a new
Proxy, it simply sends another RS message toward the Server via the
new Proxy on behalf of the Client.
In some cases, the access router and Proxy may be one and the same
node. In that case, the node would be located on the same physical
link as the Client, but its message exchanges with the Server 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: The Proxy can apply packing as discussed in Section 5.2 of
[I-D.templin-6man-omni-interface] if an opportunity arises to
concatenate multiple payload packets that will be destined to the
same neighbor.
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3.13.1. Combined Proxy/Servers
Clients may need to connect directly to Servers via INET, Direct and
VPNed interfaces (i.e., non-ANET interfaces). If the Client's
underlying interfaces all connect via the same INET partition, then
it can connect to a single controlling Server via all interfaces.
If some Client interfaces connect via different INET partitions,
however, the Client still selects a set of controlling Servers and
sends RS messages via their directly-connected Servers while using
the ADM-LLA of the controlling Server as the destination.
When a Server receives an RS with destination set to the ADM-LLA of a
controlling Server, it acts as a Proxy to forward the message to the
controlling Server while forwarding the corresponding RA reply to the
Client.
3.13.2. Detecting and Responding to Server Failures
In environments where fast recovery from Server failure is required,
Proxys SHOULD use proactive Neighbor Unreachability Detection (NUD)
to track Server reachability in a similar fashion as for
Bidirectional Forwarding Detection (BFD) [RFC5880]. Proxys can then
quickly detect and react to failures so that cached information is
re-established through alternate paths. The 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.
Proxys perform proactive NUD with Servers for which there are
currently active ANET Clients by sending continuous NS messages in
rapid succession, e.g., one message per second. The Proxy sends the
NS message via the spanning tree with the Proxy's ADM-LLA as the
source and the ADM-LLA of the Server as the destination. When the
Proxy is also sending RS messages to the Server on behalf of ANET
Clients, the resulting RA responses can be considered as equivalent
hints of forward progress. This means that the Proxy need not also
send a periodic NS if it has already sent an RS within the same
period. If the Server fails (i.e., if the Proxy ceases to receive
advertisements), the Proxy can quickly inform Clients by sending
multicast RA messages on the ANET interface.
The Proxy sends RA messages on the ANET interface with source address
set to the Server's address, destination address set to (link-local)
All-Nodes multicast, and Router Lifetime set to 0. The Proxy SHOULD
send MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated by small
delays [RFC4861]. Any Clients on the ANET that had been using the
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failed Server will receive the RA messages and associate with a new
Server.
3.13.3. Point-to-Multipoint Server Coordination
In environments where Client messaging over ANETs is bandwidth-
limited and/or expensive, Clients can enlist the services of the
Proxy to coordinate with multiple Servers in a single RS/RA message
exchange. The Client can send a single RS message to (link-local)
All-Routers multicast that includes the ID's of multiple Servers in
MS-Register sub-options of the OMNI option.
When the Proxy receives the RS and processes the OMNI option, it
sends a separate RS to each MS-Register Server ID. When the Proxy
receives an RA, it can optionally return an immediate "singleton" RA
to the Client or record the Server's ID for inclusion in a pending
"aggregate" RA message. The Proxy can then return aggregate RA
messages to the Client including multiple Server IDs in order to
conserve bandwidth. Each RA includes a proper subset of the Server
IDs from the original RS message, and the Proxy must ensure that the
message contents of each RA are consistent with the information
received from the (aggregated) Servers.
Clients can thereafter employ efficient point-to-multipoint Server
coordination under the assistance of the Proxy to reduce the number
of messages sent over the ANET while enlisting the support of
multiple Servers for fault tolerance. Clients can further include
MS-Release sub-options in IPv6 ND messages to request the Proxy to
release from former Servers via the procedures discussed in
Section 3.16.5.
The OMNI interface specification [I-D.templin-6man-omni-interface]
provides further discussion of the Client/Proxy RS/RA messaging
involved in point-to-multipoint coordination.
3.14. AERO Address Resolution
While data packets are flowing between a source and target node,
route optimization SHOULD be used. Route optimization is initiated
by the first eligible Route Optimization Source (ROS) closest to the
source as follows:
o For Clients on VPNed and Direct interfaces, the Server is the ROS.
o For Clients on ANET interfaces, the Proxy is the ROS.
o For Clients on INET interfaces, the Client itself is the ROS.
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o For correspondent nodes on INET/EUN interfaces serviced by a
Relay, the Relay is the ROS.
The route optimization procedure is conducted between the ROS and
with the target Server/Relay or the target Client itself acting as a
Route Optimization Responder (ROR) in the same manner as for IPv6 ND
Address Resolution and using the same NS/NA messaging. The target
may either be a MNP Client serviced by a Server, or a non-MNP
correspondent reachable via a Relay.
The procedures are specified in the following sections.
3.14.1. Route Optimization Initiation
While original IP packet from the source node destined a target node
arrives, the ROS sends an NS message for Address Resolution (NS(AR))
to receive a solicited NA(AR) message from a ROR. The NS(AR) message
must be no larger than the OAL minimum MPS so that its entire
contents will fit in the first fragment (i.e., as an "atomic
fragment"). When the ROS sends an NS(AR), it first creates a
neighbor cache entry for the target in the INCOMPLETE state for the
target and places the original IP packet on a short queue. The ROS
then prepares an NS(AR) that includes:
o the LLA of the ROS as the source address.
o the LLA corresponding to the original IP packet's destination as
the Target Address, e.g., for 2001:db8:1:2::10:2000 the LLA 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
destination address is ff02:0:0:0:0:1:ff10:2000.
The NS(AR) message also includes an OMNI option with no Interface
Attributes, such that the target will not create a neighbor cache
entry. The Prefix Length in the OMNI option is set to the Prefix
Length associated with the ROS's LLA.
The ROS then submits the NS(AR) message for OAL encapsulation and
fragmentation, with OAL source set to its own ULA and OAL destination
set to the MNP-ULA corresponding to the target, then sends the
resulting *NET packet (i.e., the "atomic fragment") into the spanning
tree without decrementing the network-layer TTL/Hop Limit field.
(When the ROS is a Client, it instead securely sends the *NET packet
to one of its current Servers as specified in Section 3.22. The
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Server then forwards the *NET packet into the spanning tree on behalf
of the Client.)
3.14.2. Relaying the NS(AR) *NET Packet(s)
When the Bridge receives the *NET packet from the ROS, 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 re-encapsulates and forwards the *NET
packet via the spanning tree the same as for any IPv6 router, where
it may traverse multiple OMNI link segments. The final-hop Bridge in
the spanning tree will deliver the *NET packet via a secured tunnel
to a Server or Relay that services the target.
3.14.3. Processing the NS(AR) and Sending the NA(AR)
When the Server or Relay receives the *NET packet, it examines the
OAL atomic fragment to determine that it contains an NS(AR), then
examines the NS(AR) destination to determine whether it has a
matching neighbor cache entry and/or route. If there is no match,
the ROR drops the message. Otherwise, the ROR continues processing
as follows:
o if the destination matches a Client neighbor in the DEPARTED
state, the Server inserts an ORH with destination prefix set to
the lower 64 bits of the MNP-ULA and sets the destination address
to the ADM-ULA of the Client's new Server. The (old) Server then
re-encapsulates the *NET packet, forwards it into the spanning
tree and returns from processing.
o If the NS(AR) destination matches an MNP Client neighbor cache
entry in the REACHABLE state, the ROR instead proceeds according
to whether the Client requires Proxy services. For
"disadvantaged" Clients (e.g., those on low-end links) and Clients
with complex multilink arrangements, the Server nominates itself
as the ROR and adds the NS(AR) source address to the target
Client's Report List with time set to ReportTime. Otherwise, the
Server re-encapsulates the *NET packet and forwards it to the
target Client which will act as a ROR on its own behalf.
o If the NS(AR) belongs to a non-MNP route, the ROR continues
processing without adding an entry to the Report List.
The ROR then prepares a (solicited) NA(AR) message to send back to
the ROS but does not create a neighbor cache entry. The ROR sets the
NA(AR) source address to its own LLA, sets the destination address to
the source of the solicitation and sets the Target Address to the
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target of the solicitation. The ROR then includes an OMNI option
with Prefix Length set to the length associated with the MNP-LLA.
If the target is an MNP Client, the ROR next includes Interface
Attributes in the OMNI option for each of the target Client's
underlying interfaces with current information for each interface and
with the S/T-ifIndex field in the OMNI header set to 0.
For each Interface Attributes sub-option, the ROR sets the L2ADDR
according to its own INET address for VPNed or Direct interfaces, to
the *NET address of the Proxy or to the Client's *NET address for
INET interfaces. The ROR then includes the lower 32 bits of its own
ADM-ULA (or the ADM-ULA of the Proxy/Server) as the LHS, encodes the
ADM-ULA prefix length code in the SRT field and sets the FMT code
accordingly as specified in Section 3.3.
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). If the ROR is the
Client itself, it sets the O flag to 1; if the ROR is the Server, it
instead sets the O flag to 0 (as a proxy). The ROR finally submits
the NA(AR) for OAL encapsulation with source set to its own ULA and
destination set to the source ULA of the NS(AR) message, then
performs *NET fragmentation and forwards the resulting *NET packets
into the spanning tree without decrementing the network-layer TTL/Hop
Limit field.
3.14.4. Relaying the NA(AR)
When the Bridge receives the *NET packets from the ROR, 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 re-encapsulates and forwards the *NET
packet via the spanning tree the same as for any IPv6 router, where
it may traverse multiple OMNI link segments. The final-hop Bridge in
the spanning tree will deliver the *NET packet via a secured tunnel
to a Server for the ROS.
3.14.5. Processing the NA(AR)
When the ROS receives the NA(AR) message, it processes the message
the same as for standard IPv6 Address Resolution [RFC4861]. In the
process, it caches the source ULA and all information found in the
OMNI option in the neighbor cache entry for the target. The ROS
finally sets the neighbor cache entry state to REACHABLE and sets its
lifetime to ReachableTime seconds. (When the ROS is a Client, the
solicited NA(AR) message will first be delivered via the spanning
tree to one of its current Servers, which then securely forwards the
message to the Client as discussed in Section 3.22.)
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3.14.6. Route Optimization Maintenance
Following route optimization, the ROS forwards future data packets
destined to the target via the addresses found in the cached link-
layer information. The route optimization is shared by all sources
that send packets to the target via the ROS, i.e., and not just the
source on behalf of which the route optimization was initiated.
While new data packets destined to the target are flowing through the
ROS, it sends additional NS(AR) messages to the ROR before
ReachableTime expires to receive a fresh NA(AR) message the same as
described in the previous sections (route optimization refreshment
strategies are an implementation matter, with a non-normative example
given in Appendix A.1). The ROS uses the cached ULA of the ROR
(i.e., either the ADM-ULA of the Server or the MNP-ULA of the Client
itself) as the NS(AR) OAL destination address, and sends up to
MAX_MULTICAST_SOLICIT NS(AR) messages separated by 1 second until an
NA(AR) is received. If no NA(AR) is received, the ROS assumes that
the current ROR has become unreachable and deletes the target
neighbor cache entry. Subsequent data packets will trigger a new
route optimization event (see: Section 3.14.1).
If an NA(AR) is received, the ROS then updates the neighbor cache
entry to refresh ReachableTime, while (for MNP destinations) the ROR
adds or updates the ROS address to the target's Report List and with
time set to ReportTime. While no data packets are flowing, the ROS
instead allows ReachableTime for the neighbor cache entry to expire.
When ReachableTime expires, the ROS deletes the neighbor cache entry.
Any future data packets flowing through the ROS will again trigger a
new route optimization.
The ROS may also receive unsolicited NA messages from the ROR at any
time (see: Section 3.16). If there is a neighbor cache entry for the
target, the ROS updates the link-layer information but does not
update ReachableTime since the receipt of an unsolicited NA does not
confirm that any forward paths are working. If there is no neighbor
cache entry, the ROS simply discards the unsolicited NA.
In this arrangement, the ROS holds a neighbor cache entry for the
target via the ROR, but the ROR does not hold a neighbor cache entry
for the ROS. The route optimization neighbor relationship is
therefore asymmetric and unidirectional. If the target node also has
packets to send back to the source node, then a separate route
optimization procedure is performed in the reverse direction. But,
there is no requirement that the forward and reverse paths be
symmetric.
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3.15. 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 and/
or establish NAT state. The NUD algorithm is based on periodic
control message exchanges. The algorithm may further be seeded by ND
hints of forward progress, but care must be taken to avoid inferring
reachability based on spoofed information. For example, authentic
IPv6 ND message exchanges may be considered as acceptable hints of
forward progress, while spurious data packets should not be.
AERO nodes can use standard NS/NA exchanges sent over the OMNI link
spanning tree to securely 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 two parties involved in
the NUD test the same as for standard IPv6 ND, and both messages flow
over the spanning tree). Proxys can further perform NUD to securely
verify Server reachability on behalf of their proxyed Clients.
However, a means for an ROS to test the unsecured target route
optimized paths is also necessary.
When an ROR directs an ROS to a target neighbor with one or more
link-layer addresses, the ROS can proactively test each such
unsecured route optimized path through secured NS(NUD) messages over
the spanning tree that invoke an unsecured NA(NUD) reply that travels
over the route optimized path.. (The NS(NUD) messages must therefore
include Nonce and Timestamp options that will be echoed in the
unsecured NA(NUD) replies.) While testing the paths, the ROS can
optionally continue to send packets via the spanning tree, maintain a
small queue of packets until target reachability is confirmed, or
(optimistically) allow packets to flow via the route optimized paths.
When the ROS sends an NS(NUD) message, it sets the IPv6 source to its
own address, sets the destination to the MNP-LLA of the target, and
sets the target's MNP Subnet-Router anycast address as the Target
Address. The ROS also includes an OMNI option with a single
Interface Attributes sub-option with the SRT, FMT, LHS and L2ADDR
information for its own underlying interface it wishes to test, but
sets the S/T-ifIndex field to the index for target's underlying
interface to be tested. The ROS includes a Nonce and Timestamp
option, then encapsulates the message in OAL/INET headers with its
own ULA as the source and the ULA of the target as the destination.
The ROS then forwards the NS(NUD) message toward the target via a
Server or Bridge.
When the target receives the NS(NUD) message, it creates an NA(NUD)
by reversing the OAL and IPv6 addresses and including an Interface
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Attributes sub-option with attributes for its own interface
identified by the NS(NUD) S/T-ifIndex. The target sets the NA(NUD)
S/T-ifIndex to the index of the ROS, sets the Target Address to the
same value that was in the NS(NUD), and returns the message using its
own underlying interface identified by S/T-ifIndex and destined to
the ROS's interface identified by the original Interface Attributes
sub-option.
When the ROS receives the NA(NUD) message, it can determine from the
Nonce, Timestamp and Target Address that the message matched its
NS(NUD) and that it transited the direct path from the ROR using the
selected underlying interface pair. The ROS marks route optimization
target paths that pass these NUD tests as "reachable", and those that
do not as "unreachable". These markings inform the OMNI interface
forwarding algorithm specified in Section 3.10.
Note: If the target determines that the OMNI option Interface
Attributes in the NS(NUD) is located in a different OMNI link segment
than its own interface named in the S/T-ifIndex, it instead returns
the NA(NUD) via the spanning tree while including an ORH and setting
the OAL destination address to the Subnet Router Anycast address used
by Bridges on the ROS segment. When a Bridge on the ROS segment
receives the NA(NUD), it replaces the Interface Attributes with
information for its own interface while using the ifIndex value
specific to the target.
3.16. Mobility Management and Quality of Service (QoS)
AERO is a Distributed Mobility Management (DMM) service. Each Server
is responsible for only a subset of the Clients on the OMNI link, as
opposed to a Centralized Mobility Management (CMM) service where
there is a single network mobility collective entity for all Clients.
Clients coordinate with their associated Servers via RS/RA exchanges
to maintain the DMM profile, and the AERO routing system tracks all
current Client/Server peering relationships.
Servers provide default routing and mobility/multilink services for
their dependent Clients. Clients are responsible for maintaining
neighbor relationships with their Servers through periodic RS/RA
exchanges, which also serves to confirm neighbor reachability. When
a Client's underlying interface address and/or QoS information
changes, the Client is responsible for updating the Server with this
new information. Note that when there is a Proxy in the path, the
Proxy can also perform some RS/RA exchanges on the Client's behalf.
Mobility management messaging is based on the transmission and
reception of unsolicited Neighbor Advertisement (uNA) messages. Each
uNA message sets the IPv6 destination address to (link-local) All-
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Nodes multicast to convey a general update of Interface Attributes to
(possibly) multiple recipients, or to a specific unicast LLA to
announce a departure event to a specific recipient. Implementations
must therefore examine the destination address to determine the
nature of the mobility event (i.e., update vs departure).
Mobility management considerations are specified in the following
sections.
3.16.1. Mobility Update Messaging
Servers accommodate Client mobility, multilink and/or QoS change
events by sending unsolicited NA (uNA) messages to each ROS in the
target Client's Report List. When a Server sends a uNA message, it
sets the IPv6 source address to the Client's MNP-LLA, sets the
destination address to (link-local) All-Nodes multicast and sets the
Target Address to the Client's Subnet-Router anycast address. The
Server also includes an OMNI option with Prefix Length set to the
length associated with the Client's MNP-LLA, with Interface
Attributes for the target Client's underlying interfaces and with the
OMNI header S/T-ifIndex set to 0. The Server then sets the NA R flag
to 1, the S flag to 0 and the O flag to 1, then encapsulates the
message in an OAL header with source set to its own ADM-ULA and
destination set to the ULA of the ROS and sends the message into the
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
uNA messages will be delivered with high probability, but in any case
the Server can optionally send up to MAX_NEIGHBOR_ADVERTISEMENT uNAs
to each ROS to increase the likelihood that at least one will be
received.
When the ROS receives a uNA message prepared as above, it ignores the
message if there is no existing neighbor cache entry for the Client.
Otherwise, it uses the included OMNI option information to update the
neighbor cache entry, but does not reset ReachableTime since the
receipt of an unsolicited NA message from the target Server does not
provide confirmation that any forward paths to the target Client are
working.
If uNA messages are lost, the ROS may be left with stale address and/
or QoS information for the Client for up to ReachableTime seconds.
During this time, the ROS can continue sending packets according to
its stale neighbor cache information. When ReachableTime is close to
expiring, the ROS will re-initiate route optimization and receive
fresh link-layer address information.
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In addition to sending uNA messages to the current set of ROSs for
the Client, the Server also sends uNAs to the MNP-ULA associated with
the link-layer address for any underlying interface for which the
link-layer address has changed. These uNA messages update an old
Proxy/Server that cannot easily detect (e.g., without active probing)
when a formerly-active Client has departed. When the Server sends
the uNA, it sets the IPv6 source address to the Client's MNP-LLA,
sets the destination address to the old Proxy/Server's ADM-LLA, and
sets the Target Address to the Client's Subnet-Router anycast
address. The Server also includes an OMNI option with Prefix Length
set to the length associated with the Client's MNP-LLA, with
Interface Attributes for the changed underlying interface, and with
the OMNI header S/T-ifIndex set to 0. The Server then sets the NA R
flag to 1, the S flag to 0 and the O flag to 1, then encapsulates the
message in an OAL header with source set to its own ADM-ULA and
destination set to the ADM-ULA of the old Proxy/Server and sends the
message into the spanning tree.
3.16.2. Announcing Link-Layer Address and/or QoS Preference Changes
When a Client needs to change its underlying interface addresses and/
or QoS preferences (e.g., due to a mobility event), either the Client
or its Proxys send RS messages to the Server via the spanning tree
with an OMNI option that includes Interface attributes with the new
link quality and address information.
Up to MAX_RTR_SOLICITATIONS RS messages MAY be sent in parallel with
sending actual data packets in case one or more RAs are lost. If all
RAs are lost, the Client SHOULD re-associate with a new Server.
When the Server receives the Client's changes, it sends uNA messages
to all nodes in the Report List the same as described in the previous
section.
3.16.3. 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 Server via the underlying interface with an OMNI option that
includes Interface Attributes with appropriate link quality values
and with link-layer address information for the new link.
3.16.4. Deactivating Existing Links
When a Client needs to deactivate an existing underlying interface,
it sends an RS or uNA message to its Server with an OMNI option with
appropriate Interface Attribute values - in particular, the link
quality value 0 assures that neighbors will cease to use the link.
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If the Client needs to send RS/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.
Note that when a Client deactivates an underlying interface,
neighbors that have received the RS/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 ifIndex at a later point in time, when it will send RS/uNA
messages with fresh Interface Attributes to update any neighbors.
3.16.5. Moving Between Servers
The Client performs the procedures specified in Section 3.12.2 when
it first associates with a new Server or renews its association with
an existing Server. The Client also includes MS-Release identifiers
in the RS message OMNI option per [I-D.templin-6man-omni-interface]
if it wants the new Server to notify any old Servers from which the
Client is departing.
When the new Server receives the Client's RS message, it returns an
RA as specified in Section 3.12.3 and sends up to
MAX_NEIGHBOR_ADVERTIISEMENT uNA messages to any old Servers listed in
OMNI option MS-Release identifiers. When the new Server sends a uNA
message, it sets the IPv6 source address to the Client's MNP-LLA,
sets the destination address to the old Server's ADM-LLA, and sets
the Target Address to the Client's Subnet-Router anycast address.
The new Server also includes an OMNI option with Prefix Length set to
the length associated with the Client's MNP-LLA, with Interface
Attributes for its own underlying interface, and with the OMNI header
S/T-ifIndex set to 0. The new Server then sets the NA R flag to 1,
the S flag to 0 and the O flag to 1, then encapsulates the message in
an OAL header with source set to its own ADM-ULA and destination set
to the ADM-ULA of the old Server and sends the message into the
spanning tree.
When an old Server receives the uNA, it changes the Client's neighbor
cache entry state to DEPARTED, sets the link-layer address of the
Client to the new Server's ADM-ULA, and resets DepartTime. After a
short delay (e.g., 2 seconds) the old Server withdraws the Client's
MNP from the routing system. After DepartTime expires, the old
Server deletes the Client's neighbor cache entry.
The old Server also iteratively forwards a copy of the uNA message to
each ROS in the Client's Report List by changing the OAL destination
address to the ULA of the ROS while leaving all other fields of the
message unmodified. When the ROS receives the uNA, it examines the
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Target address to determine the correct neighbor cache entry and
verifies that the IPv6 destination address matches the old Server.
The ROS then caches the IPv6 source address as the new Server for the
existing neighbor cache entry and marks the entry as STALE. While in
the STALE state, the ROS allows new data packets to flow according to
any existing cached link-layer information and sends new NS(AR)
messages using its own ULA as the OAL source and the ADM-ULA of the
new Server as the OAL destination address to elicit NA messages that
reset the neighbor cache entry state to REACHABLE. If no new NA
message is received for 10 seconds while in the STALE state, the ROS
deletes the neighbor cache entry.
Clients SHOULD NOT move rapidly between 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 Server include a
Server that has gone unreachable, topological movements of
significant distance, movement to a new geographic region, movement
to a new OMNI link segment, etc.
When a Client moves to a new Server, some of the fragments of a
multiple fragment packet may have already arrived at the old Server
while others are en route to the new Server, however no special
attention in the reassembly algorithm is necessary when re-routed
fragments are simply treated as loss.
3.17. Multicast
The AERO Client provides an IGMP (IPv4) [RFC2236] or MLD (IPv6)
[RFC3810] proxy service for its EUNs and/or hosted applications
[RFC4605]. The Client forwards IGMP/MLD messages over any of its
underlying interfaces for which group membership is required. The
IGMP/MLD messages may be further forwarded by a first-hop ANET access
router acting as an IGMP/MLD-snooping switch [RFC4541], then
ultimately delivered to an AERO Proxy/Server acting as a Protocol
Independent Multicast - Sparse-Mode (PIM-SM, or simply "PIM")
Designated Router (DR) [RFC7761]. AERO Relays also act as PIM
routers (i.e., the same as AERO Proxys/Servers) on behalf of nodes on
INET/EUN networks. The behaviors identified in the following
sections correspond to Source-Specific Multicast (SSM) and Any-Source
Multicast (ASM) operational modes.
3.17.1. Source-Specific Multicast (SSM)
When an ROS (i.e., an AERO Proxy/Server/Relay) "X" 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
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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
originates a separate copy of the Join/Prune for each (S,G) in the
message using its own LLA as the source address and ALL-PIM-ROUTERS
as the destination address. X then encapsulates each message in an
OAL header with source address set to the ULA of X and destination
address set to S then forwards the message into the spanning tree,
which delivers it to AERO Server/Relay "Y" that services S. At the
same time, if the message was a Join, X sends a route-optimization NS
message toward each S the same as discussed in Section 3.14. The
resulting NAs will return the LLA for the prefix that matches S as
the network-layer source address and with an OMNI option with the ULA
corresponding to any underlying interfaces that are currently
servicing S.
When Y processes the Join/Prune message, if S located behind any
INET, Direct, or VPNed interfaces Y acts as a PIM router and updates
its MRIB to list X as the next hop in the reverse path. If S is
located behind any Proxys "Z"*, Y also forwards the message to each
Z* over the spanning tree while continuing to use the LLA of X as the
source address. Each Z* then updates its MRIB accordingly and
maintains the LLA of X as the next hop in the reverse path. Since
the Bridges do not examine network layer control messages, this means
that the (reverse) multicast tree path is simply from each Z* (and/or
Y) to X with no other multicast-aware routers in the path. If any Z*
(and/or Y) is located on the same OMNI link segment as X, the
multicast data traffic sent to X directly using OAL/INET
encapsulation instead of via a Bridge.
Following the initial Join/Prune and NS/NA messaging, X maintains a
neighbor cache entry 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 neighbor cache entry alive for up to t_periodic
seconds [RFC7761]. If no new Joins are received within t_periodic
seconds, X allows the neighbor cache entry to expire. Finally, if X
receives any additional Join/Prune messages for (S,G) it forwards the
messages to each Y and Z* in the neighbor cache entry over the
spanning tree.
At some later time, Client C that holds an MNP for source S may
depart from a first Proxy Z1 and/or connect via a new Proxy Z2. In
that case, Y sends an unsolicited NA message to X the same as
specified for unicast mobility in Section 3.16. When X receives the
unsolicited NA message, it updates its neighbor cache entry for the
LLA for source S and sends new Join messages to any new Proxys Z2.
There is no requirement to send any Prune messages to old Proxys Z1
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since source S will no longer source any multicast data traffic via
Z1. Instead, the multicast state for (S,G) in Proxy Z1 will soon
time out since no new Joins will arrive.
After some later time, C may move to a new Server Y2 and depart from
old Sever Y1. In that case, Y1 sends Join messages for any of C's
active (S,G) groups to Y2 while including its own LLA as the source
address. This causes Y2 to include Y1 in the multicast forwarding
tree during the interim time that Y1's neighbor cache entry for C is
in the DEPARTED state. At the same time, Y1 sends an unsolicited NA
message to X with an OMNI option with S/T-ifIndex in the header set
to 0 and a release indication to cause X to release its neighbor
cache entry. X then sends a new Join message to S via the spanning
tree and re-initiates route optimization the same as if it were
receiving a fresh Join message from a node on a downstream link.
3.17.2. Any-Source Multicast (ASM)
When an ROS X acting as a PIM router receives a Join/Prune from a
node on its downstream interfaces containing one or more (*,G) pairs,
it updates its Multicast Routing Information Base (MRIB) accordingly.
X then forwards a copy of the message to the Rendezvous Point (RP) R
for each G over the spanning tree. X uses its own LLA as the source
address and ALL-PIM-ROUTERS as the destination address, then
encapsulates each message in an OAL header with source address set to
the ULA of X and destination address set to R, then sends the message
into the spanning tree. At the same time, if the message was a Join
X initiates NS/NA route optimization the same as for the SSM case
discussed in Section 3.17.1.
For each source S that sends multicast traffic to group G via R, the
Proxy/Server Z* for the Client that aggregates S encapsulates the
packets in PIM Register messages and forwards them to R via the
spanning tree, which may then elect to send a PIM Join to Z*. This
will result in an (S,G) tree rooted at Z* with R as the next hop so
that R will begin to receive two copies of the packet; one native
copy from the (S, G) tree and a second copy from the pre-existing (*,
G) tree that still uses PIM Register encapsulation. R can then issue
a PIM Register-stop message to suppress the Register-encapsulated
stream. At some later time, if C moves to a new Proxy/Server Z*, it
resumes sending packets via PIM Register encapsulation via the new
Z*.
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 3.17.1. Once the (S,G) tree is
established, the listeners can send (S, G) Prune messages to R so
that multicast packets for group G sourced by S will only be
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delivered via the (S, G) tree and not from the (*, G) tree rooted at
R. All mobility considerations discussed for SSM apply.
3.17.3. 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.
3.18. 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, Servers and Proxys,
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, with each VLAN distinguished by a
different SRT "color" (see: Section 3.2.5).
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
packets destined to a target via the correct OMNI link.
In a first alternative, if each OMNI link services different MSPs,
then 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
will then direct the packet over multiple hops to the target.
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3.19. 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 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 Server, the 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.
3.20. Transition 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 Relays on each INET partition, with each Relay
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
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 Relays.
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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3.21. Detecting and Reacting to Server and Bridge Failures
In environments where rapid failure recovery is required, 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.
Servers and Bridges maintain BFD sessions in parallel with their BGP
peerings. If a 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.
Proxys SHOULD use proactive NUD for Servers for which there are
currently active ANET Clients in a manner that parallels BFD, i.e.,
by sending unicast NS messages in rapid succession to receive
solicited NA messages. When the Proxy is also sending RS messages on
behalf of ANET Clients, the RS/RA messaging can be considered as
equivalent hints of forward progress. This means that the Proxy need
not also send a periodic NS if it has already sent an RS within the
same period. If a Server fails, the Proxy will cease to receive
advertisements and can quickly inform Clients of the outage by
sending multicast RA messages on the ANET interface.
The Proxy sends multicast RA messages with source address set to the
Server's address, destination address set to (link-local) All-Nodes
multicast, and Router Lifetime set to 0. The Proxy SHOULD send
MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated by small delays
[RFC4861]. Any Clients on the ANET interface that have been using
the (now defunct) Server will receive the RA messages and associate
with a new Server.
3.22. AERO Clients on the Open Internet
AERO Clients that connect to the open Internet via INET interfaces
can establish a VPN or direct link to securely connect to a Server in
a "tethered" arrangement with all of the Client's traffic transiting
the Server. Alternatively, the Client can associate with an INET
Server using UDP/IP encapsulation and control message securing
services as discussed in the following sections.
When a Client's OMNI interface enables an INET underlying interface,
it first determines whether the interface is likely to be behind a
NAT. For IPv4, the Client assumes it is on the open Internet if the
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INET address is not a special-use IPv4 address per [RFC3330].
Similarly for IPv6, the Client assumes it is on the open Internet if
the INET address is a Global Unicast Address (GUA) [RFC4291].
Otherwise, the Client assumes it may be behind one or several NATs.
The Client then prepares an RS message with IPv6 source address set
to its MNP-LLA, with IPv6 destination set to (link-local) All-Routers
multicast and with an OMNI option with underlying interface
attributes. If the Client believes that it is on the open Internet,
it SHOULD include an L2ADDR in the Interface Attributes sub-option
corresponding to the underlying interface; otherwise, it MAY omit
L2ADDR. If the underlying address is IPv4, the Client includes the
Port Number and IPv4 address written in obfuscated form [RFC4380] as
discussed in Section 3.3. If the underlying interface address is
IPv6, the Client instead includes the Port Number and IPv6 address in
obfuscated form. The Client finally includes a HIP "Initiator"
message sub-option in the OMNI option
[I-D.templin-6man-omni-interface] to provide message authentication
and performs OAL encapsulation and fragmentation if necessary. The
Client then encapsulates each fragment in UDP/IP headers, sets the
UDP/IP source to its INET address and UDP port, sets the UDP/IP
destination to the Server's INET address and the AERO service port
number (8060), then sends the (whole or fragmented) message to the
Server.
When the Server receives the RS, it performs OAL reassembly if
necessary then authenticates the message and registers the Client's
MNP and INET interface information according to the OMNI option
parameters. If the RS message OMNI option includes Interface
Attributes with an L2ADDR, the Server compares the encapsulation IP
address and UDP port number with the (unobfuscated) values. If the
values are the same, the Server caches the Client's information as
"INET" addresses meaning that the Client is likely to accept direct
messages without requiring NAT traversal exchanges. If the values
are different (or, if the OMNI option did not include an L2ADDR) the
Server instead caches the Client's information as "mapped" addresses
meaning that NAT traversal exchanges may be necessary.
The Server then prepares an RA message with IPv6 source and
destination set corresponding to the addresses in the RS, and with an
OMNI option with an Origin Indication sub-option per
[I-D.templin-6man-omni-interface] with the mapped and obfuscated Port
Number and IP address observed in the encapsulation headers. The
Server also includes a HIP "Responder" message sub-option per
[I-D.templin-6man-omni-interface] that contains an acknowledgement of
the update sent by the Client. The Server then performs OAL
encapsulation and fragmentation if necessary, and encapsulates each
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fragment in UDP/IP headers with addresses set per the L2ADDR
information in the neighbor cache entry for the Client.
When the Client receives the RA message, it performs OAL reassembly
if necessary, authenticates the HIP "Responder" message, then
compares the mapped Port Number and IP address from the Origin
Indication sub-option with its own address. If the addresses are the
same, the Client assumes the open Internet / Cone NAT principle; if
the addresses are different, the Client instead assumes that further
qualification procedures are necessary to detect the type of NAT and
proceeds according to standard procedures [RFC6081][RFC4380].
After the Client has registered its INET interfaces in such RS/RA
exchanges it sends periodic RS messages to receive fresh RA messages
before the Router Lifetime received on each INET interface expires.
The Client also maintains default routes via its Servers, i.e., the
same as described in earlier sections.
When the Client sends messages to target IP addresses, it also
invokes route optimization per Section 3.14 using IPv6 ND address
resolution messaging. The Client sends the NS(AR) message to the
Server with an OMNI option with a HIP "Update/Sequence" message sub-
option. The Client sets the NS source address to the Client's MNP-
LLA and destination address to the target solicited node multicast
address. The Client wraps the NS message in an OAL header with
source address set to its own MNP-ULA and destination address set to
the Server's ADM-ULA. The Client then performs OAL fragmentation if
necessary, wraps each fragment in a UDP/IP header and sends it to the
Server.
When the Server receives the OAL-encapsulated NS, it performs OAL
reassembly if necessary. The Server then authenticates the message
by processing the HIP message sub-option and sends a corresponding
NS(AR) message over the spanning tree the same as if it were the ROS,
but with the OAL source address set to the Server's ADM-ULA, with
destination set to the MNP-ULA of the target, and with an OMNI option
that includes no sub-options. When the ROR receives the NS(AR), it
adds the Server's ADM-ULA and Client's MNP-LLA to the target's Report
List, and returns an NA(AR) with OMNI option information for the
target including all of the target's Interface Attributes. The ROR
sets the NA(AR) source address to the target's MNP-LLA and sets the
destination address to the Client's MNP-LLA, then sets the OAL source
address to the ADM-ULA of the ROR and the destination to the ADM-ULA
of the Server. When the Server receives the NA(AR) message, it
rewrites the OAL source address to its own ADM-ULA and the
destination address to the MNP-ULA of the Client, then includes a HIP
"Update/Acknowledge" message sub-option in the OMNI option, performs
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OAL fragmentation if necessary, wraps each fragment in UDP/IP
headers, and sends it to the Client.
Following route optimization for targets in the same OMNI link
segment, if the target's L2ADDR is on the open INET, the Client
forwards data packets directly to the target INET address. If the
target is behind a NAT, the Client first establishes NAT state for
the L2ADDR using the "direct bubble" and NUD mechanisms discussed in
Section 3.10.1. The Client continues to send data packets via its
Server until NAT state is populated, then begins forwarding packets
via the direct path through the NAT to the target. For targets in
different OMNI link segments, the Client uses OAL/ORH encapsulation
and forwards data packets to the Bridge that returned the NA message.
The ROR may return uNAs via the Server if the target moves, and the
Server will send corresponding uNAs to the Client with a HIP "Notify"
authentication message. The Client can also send NUD messages to
test forward path reachability even though there is no security
association between the Client and the target.
The Client sends IP packets to route-optimized neighbors in the same
OMNI link segment no larger than the absolute/path MCS in one piece
and without OAL encapsulation. For larger IP packets, the Client
applies OAL encapsulation and fragmentation if necessary according to
Section 3.9, with OAL header with source set to its own MNP-ULA and
destination set to the MNP-ULA of the target. The Client then
encapsulates each raw or OAL-encapsulated IP packet/fragment in a
UDP/IP header and sends them to the next hop.
Note: The NAT traversal procedures specified in this document are
applicable for Cone, Address-Restricted and Port-Restricted NATs
only. While future updates to this document may specify procedures
for other NAT variations (e.g., hairpinning and various forms of
Symmetric NATs), it should be noted that continuous communications
are always possible through forwarding via a Server even if NAT
traversal is not employed.
Note: Following the initial HIP Initiator/Responder exchange, AERO
Clients with OMNI interfaces configured over the open Internet
maintain HIP associations through the transmission of IPv6 ND
messages that include OMNI options with HIP "Update" and "Notify"
messages. OMNI interfaces use the HIP "Update" message when an
acknowledgement is required, and use the "Notify" message in
unacknowledged isolated IPv6 ND messages (e.g., unsolicited NAs).
Note: Servers on the open Internet that act as Proxys authenticate
and remove OMNI option HIP message sub-options from RSes they forward
from the MN to another Server, and insert and sign HIP message and
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Origin Indication sub-options in RAs they forward from another Server
to the MN. Conversely, Servers that act as Proxys forward without
processing any MNP registration/delegation information in RS/RA
message exchanges between MNs and other Servers. The Server acting
as a Proxy is therefore responsible for MN authentication, while the
other Servers are responsible for registering/delegating MNPs (noting
that the same node can act as both Proxy and Server).
3.23. 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-interface]) 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.
AERO Release-3.0.2 was tagged on October 15, 2020, and is undergoing
internal testing. Additional internal releases expected within the
coming months, with first public release expected end of 1H2021.
5. IANA Considerations
The IANA is instructed to assign a new type value TBD1 in the IPv6
Routing Types registry.
The IANA has assigned the UDP port number "8060" for an earlier
experimental first version of AERO [RFC6706]. This document
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obsoletes [RFC6706], and together with
[I-D.templin-6man-omni-interface] reclaims the UDP port number "8060"
for 'aero' as the service port for UDP/IP encapsulation. (Note that,
although [RFC6706] was not widely implemented or deployed, any
messages coded to that specification can be easily distinguished and
ignored since they use the invalid ICMPv6 message type number '0'.)
This document makes no request of IANA, since
[I-D.templin-6man-omni-interface] already provides instructions.
No further IANA actions are required.
6. Security Considerations
AERO Bridges configure secured tunnels with AERO Servers, Relays and
Proxys 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 spanning tree topology. Therefore, control messages
exchanged between any pair of OMNI link neighbors on the spanning
tree are already secured.
AERO Servers, Relays and Proxys targeted by a route optimization may
also receive data packets directly from arbitrary nodes in INET
partitions instead of via the spanning tree. For INET partitions
that apply effective ingress filtering to defeat source address
spoofing, the simple data origin authentication procedures in
Section 3.8 can be applied.
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 INET partition
neighbors. Option 1) would result in longer routes than necessary
and traffic concentration on critical infrastructure elements.
Option 2) could be coordinated by establishing a secured tunnel on-
demand instead of performing an NS/NA exchange in the route
optimization procedures. Procedures for establishing on-demand
secured tunnels are out of scope.
AERO Clients that connect to secured ANETs need not apply security to
their ND messages, since the messages will be intercepted by a
perimeter Proxy that applies security on its INET-facing interface as
part of the 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.
When a VPN or direct link may be impractical, however, the
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authentication services specified in [RFC7401] and/or [RFC4380]
should be applied.
Application endpoints SHOULD use application-layer security services
such as 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 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 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 by connecting 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 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
other nodes via some form of Internet connection sharing such as
tethering.)
The MAP list MUST be well-managed and secured from unauthorized
tampering, even though the list contains only public information.
The MAP list 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.).
SRH authentication facilities are specified in [RFC8754].
Security considerations for accepting link-layer ICMP messages and
reflected packets are discussed throughout the document.
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Security considerations for IPv6 fragmentation and reassembly are
discussed in [I-D.templin-6man-omni-interface].
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, Brian Carpenter,
Wojciech Dec, Pavel Drasil, Ralph Droms, Adrian Farrel, Nick Green,
Sri Gundavelli, Brian Haberman, Bernhard Haindl, Joel Halpern, Tom
Herbert, Sascha Hlusiak, Lee Howard, Zdenek Jaron, Andre Kostur,
Hubert Kuenig, Ted Lemon, Andy Malis, Satoru Matsushima, Tomek
Mrugalski, Madhu Niraula, Alexandru Petrescu, Behcet Saikaya, Michal
Skorepa, Joe Touch, Bernie Volz, Ryuji Wakikawa, Tony Whyman, Lloyd
Wood and James Woodyatt. Members of the IESG also provided valuable
input during their review process that greatly improved the document.
Special thanks go to Stewart Bryant, Joel Halpern and Brian Haberman
for their shepherding guidance during the publication of the AERO
first edition.
This work has further been encouraged and supported by Boeing
colleagues including 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, Rob Muszkiewicz, Sean O'Sullivan, Vijay
Rajagopalan, Greg Saccone, Rod Santiago, 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. Kyle Bae, Wayne
Benson, Katie Tran and Eric Yeh are especially acknowledged for
implementing the AERO functions as extensions to the public domain
OpenVPN distribution.
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]
o Virtual Enterprise Traversal (VET)
[RFC5558][I-D.templin-intarea-vet]
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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-interface]
Templin, F. and T. Whyman, "Transmission of IP Packets
over Overlay Multilink Network (OMNI) Interfaces", draft-
templin-6man-omni-interface-69 (work in progress), January
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>.
[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>.
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[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>.
[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>.
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[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-24 (work in progress), January
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-02 (work in progress), October 2020.
[I-D.ietf-intarea-frag-fragile]
Bonica, R., Baker, F., Huston, G., Hinden, R., 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]
Jeong, J., "IPv6 Wireless Access in Vehicular Environments
(IPWAVE): Problem Statement and Use Cases", draft-ietf-
ipwave-vehicular-networking-19 (work in progress), July
2020.
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[I-D.ietf-rtgwg-atn-bgp]
Templin, F., Saccone, G., Dawra, G., Lindem, A., and V.
Moreno, "A Simple BGP-based Mobile Routing System for the
Aeronautical Telecommunications Network", draft-ietf-
rtgwg-atn-bgp-10 (work in progress), January 2021.
[I-D.templin-6man-dhcpv6-ndopt]
Templin, F., "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., "The Subnetwork Encapsulation and Adaptation
Layer (SEAL)", draft-templin-intarea-seal-68 (work in
progress), January 2014.
[I-D.templin-intarea-vet]
Templin, F., "Virtual Enterprise Traversal (VET)", draft-
templin-intarea-vet-40 (work in progress), May 2013.
[I-D.templin-ipwave-uam-its]
Templin, F., "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., "The Interior Routing Overlay Network
(IRON)", draft-templin-ironbis-16 (work in progress),
March 2014.
[I-D.templin-v6ops-pdhost]
Templin, F., "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>.
[RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
NAT64: Network Address and Protocol Translation from IPv6
Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146,
April 2011, <https://www.rfc-editor.org/info/rfc6146>.
[RFC6179] Templin, F., Ed., "The Internet Routing Overlay Network
(IRON)", RFC 6179, DOI 10.17487/RFC6179, March 2011,
<https://www.rfc-editor.org/info/rfc6179>.
[RFC6221] Miles, D., Ed., Ooghe, S., Dec, W., Krishnan, S., and A.
Kavanagh, "Lightweight DHCPv6 Relay Agent", RFC 6221,
DOI 10.17487/RFC6221, May 2011,
<https://www.rfc-editor.org/info/rfc6221>.
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[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>.
[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>.
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[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>.
[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 3.14 results in the route
optimization source (ROS) creating a neighbor cache entry for the
target neighbor. The neighbor cache entry is maintained for at most
ReachableTime seconds and then deleted unless updated. In order to
refresh the neighbor cache entry lifetime before the ReachableTime
timer expires, the specification requires implementations to issue a
new NS/NA exchange to reset ReachableTime while data packets are
still flowing. However, the decision of when to initiate a new NS/NA
exchange and to perpetuate the process is left as an implementation
detail.
One possible strategy may be to monitor the neighbor cache entry
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 to receive a new NA. If no data packets have been
sent, wait for 5 additional seconds and send an immediate NS 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, delete the neighbor cache entry.
The monitoring of the neighbor data packet traffic therefore becomes
an asymmetric ongoing process during the neighbor cache entry
lifetime. If the neighbor cache entry expires, future data packets
will trigger a new NS/NA exchange while the packets themselves are
delivered over a longer path until route optimization state is re-
established.
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A.2. Implicit Mobility Management
OMNI interface neighbors MAY provide a configuration option that
allows them to perform implicit mobility management in which no 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 neighbor cache entry
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 QoS preferences. If the Direct
interface has the highest QoS preference, then the Client's IP
packets are transmitted directly to the peer without going through an
ANET/INET. If other interfaces have higher QoS preferences, then the
Client's IP packets are transmitted via a different interface, which
may result in the inclusion of Proxys, Servers and Bridges in the
communications path. Direct interfaces must be tested periodically
for reachability, e.g., via NUD.
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 Servers can be standard dedicated server platforms, but most
often will be deployed as virtual machines in the cloud. The only
requirements for Servers are that they can run the AERO user-level
code and have at least one network interface connection to the INET.
As with Bridges, Servers must be provisioned, supported and managed
by the INET administrative authority. Cost for purchasing,
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configuring and managing Servers is nominal especially for virtual
Servers hosted in the cloud.
AERO Proxys are most often standard dedicated server platforms with
one network interface connected to the ANET and a second interface
connected to an INET. As with Servers, the only requirements are
that they can run the AERO user-level code and have at least one
interface connection to the INET. Proxys 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 can be any dedicated server or COTS router platform
connected to INETs and/or EUNs. 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 Server, and can route between the MNP and non-MNP address
spaces.
A.5. AERO Server Failure Implications
AERO Servers may appear as a single point of failure in the
architecture, but such is not the case since all Servers on the link
provide identical services and loss of a Server does not imply
immediate and/or comprehensive communication failures. Although
Clients typically associate with a single Server at a time, Server
failure is quickly detected and conveyed by Bidirectional Forward
Detection (BFD) and/or proactive NUD allowing Clients to migrate to
new Servers.
If a 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 Server
fails, unsolicited NA messages may be lost but proxy 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 Server for an extended timeframe (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 Server
relationship, after which time continuous communications will resume.
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Therefore, providing many Servers on the link with high availability
profiles provides resilience against loss of individual Servers and
assurance that Clients can establish new Server relationships quickly
in event of a 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
Servers and selects one Server to connect to. 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 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.
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
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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
or more AERO Server addresses through the mechanisms discussed in
earlier sections. Each 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 Server
ADM-LLAs at each point. It then selects one AERO Server address, and
engages in RS/RA exchanges with the same Server from all ANET
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connections. The Client remains with this Server unless or until the
Server fails, in which case it can switch over to an alternate
Server. The Client can likewise switch over to a different 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 draft-templin-intarea-6706bis-61 to draft-templin-
intrea-6706bis-62:
o New sub-section on OMNI Neighbor Interface Attributes
Changes from draft-templin-intarea-6706bis-59 to draft-templin-
intrea-6706bis-60:
o Removed all references to S/TLLAO - all Interface Attributes are
now maintained completely in the OMNI option.
Changes from draft-templin-intarea-6706bis-58 to draft-templin-
intrea-6706bis-59:
o The term "Relay" used in older draft versions is now "Bridge".
"Relay" now refers to what was formally called: "Gateway".
o Fine-grained cleanup of Forwarding Algorithm; IPv6 ND message
addressing; OMNI Prefix Lengths, etc.
Changes from draft-templin-intarea-6706bis-54 to draft-templin-
intrea-6706bis-55:
o Updates on Segment Routing and S/TLLAO contents.
o Various editorials and addressing cleanups.
Changes from draft-templin-intarea-6706bis-52 to draft-templin-
intrea-6706bis-53:
o Normative reference to the OMNI spec, and remove portions that are
already specified in OMNI.
o Renamed "AERO interface/link" to "OMIN interface/link" throughout
the document.
o Truncated obsolete back section matter.
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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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