Network Working Group F. Templin, Ed.
Internet-Draft Boeing Research & Technology
Obsoletes: rfc5320, rfc5558, rfc5720, March 23, 2021
rfc6179, rfc6706 (if
approved)
Intended status: Standards Track
Expires: September 24, 2021
Automatic Extended Route Optimization (AERO)
draft-templin-intarea-6706bis-99
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. Secure 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 24, 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) . . . . . . . . 12
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 . . . . . . . . . 16
3.2.3. AERO Routing System . . . . . . . . . . . . . . . . . 17
3.2.4. OMNI Link Segment Routing . . . . . . . . . . . . . . 19
3.2.5. Segment Routing Topologies (SRTs) . . . . . . . . . . 23
3.2.6. Segment Routing For OMNI Link Selection . . . . . . . 24
3.2.7. Segment Routing Within the OMNI Link . . . . . . . . 24
3.3. OMNI Interface Characteristics . . . . . . . . . . . . . 25
3.4. OMNI Interface Initialization . . . . . . . . . . . . . . 27
3.4.1. AERO Proxy/Server and Relay Behavior . . . . . . . . 27
3.4.2. AERO Client Behavior . . . . . . . . . . . . . . . . 28
3.4.3. AERO Bridge Behavior . . . . . . . . . . . . . . . . 28
3.5. OMNI Interface Neighbor Cache Maintenance . . . . . . . . 28
3.5.1. OMNI Neighbor Interface Attributes . . . . . . . . . 30
3.5.2. OMNI Neighbor Advertisement Message Flags . . . . . . 30
3.6. OMNI Interface Encapsulation and Re-encapsulation . . . . 31
3.7. OMNI Interface Decapsulation . . . . . . . . . . . . . . 31
3.8. OMNI Interface Data Origin Authentication . . . . . . . . 31
3.9. OMNI Interface MTU . . . . . . . . . . . . . . . . . . . 32
3.10. OMNI Interface Forwarding Algorithm . . . . . . . . . . . 33
3.10.1. Client Forwarding Algorithm . . . . . . . . . . . . 34
3.10.2. Proxy/Server Forwarding Algorithm . . . . . . . . . 35
3.10.3. Bridge Forwarding Algorithm . . . . . . . . . . . . 37
3.11. OMNI Interface Error Handling . . . . . . . . . . . . . . 39
3.12. AERO Router Discovery, Prefix Delegation and
Autoconfiguration . . . . . . . . . . . . . . . . . . . . 41
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3.12.1. AERO Service Model . . . . . . . . . . . . . . . . . 42
3.12.2. AERO Client Behavior . . . . . . . . . . . . . . . . 42
3.12.3. AERO Proxy/Server Behavior . . . . . . . . . . . . . 44
3.13. The AERO Proxy Function . . . . . . . . . . . . . . . . . 47
3.13.1. Detecting and Responding to Proxy/Server Failures . 50
3.13.2. Point-to-Multipoint Server Coordination . . . . . . 51
3.14. AERO Address Resolution . . . . . . . . . . . . . . . . . 51
3.14.1. Route Optimization Initiation . . . . . . . . . . . 52
3.14.2. Relaying the NS(AR) *NET Packet(s) . . . . . . . . . 53
3.14.3. Processing the NS(AR) and Sending the NA(AR) . . . . 53
3.14.4. Relaying the NA(AR) . . . . . . . . . . . . . . . . 55
3.14.5. Processing the NA(AR) . . . . . . . . . . . . . . . 55
3.14.6. Route Optimization Maintenance . . . . . . . . . . . 56
3.15. Neighbor Unreachability Detection (NUD) . . . . . . . . . 57
3.16. Mobility Management and Quality of Service (QoS) . . . . 59
3.16.1. Mobility Update Messaging . . . . . . . . . . . . . 59
3.16.2. Announcing Link-Layer Address and/or QoS Preference
Changes . . . . . . . . . . . . . . . . . . . . . . 60
3.16.3. Bringing New Links Into Service . . . . . . . . . . 61
3.16.4. Deactivating Existing Links . . . . . . . . . . . . 61
3.16.5. Moving Between Proxy/Servers . . . . . . . . . . . . 61
3.17. Multicast . . . . . . . . . . . . . . . . . . . . . . . . 63
3.17.1. Source-Specific Multicast (SSM) . . . . . . . . . . 63
3.17.2. Any-Source Multicast (ASM) . . . . . . . . . . . . . 65
3.17.3. Bi-Directional PIM (BIDIR-PIM) . . . . . . . . . . . 65
3.18. Operation over Multiple OMNI Links . . . . . . . . . . . 65
3.19. DNS Considerations . . . . . . . . . . . . . . . . . . . 66
3.20. Transition/Coexistence Considerations . . . . . . . . . . 67
3.21. Detecting and Reacting to Server and Bridge Failures . . 67
3.22. AERO Clients on the Open Internet . . . . . . . . . . . . 68
3.23. Time-Varying MNPs . . . . . . . . . . . . . . . . . . . . 71
4. Implementation Status . . . . . . . . . . . . . . . . . . . . 72
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 72
6. Security Considerations . . . . . . . . . . . . . . . . . . . 72
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 74
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 76
8.1. Normative References . . . . . . . . . . . . . . . . . . 76
8.2. Informative References . . . . . . . . . . . . . . . . . 77
Appendix A. Non-Normative Considerations . . . . . . . . . . . . 84
A.1. Implementation Strategies for Route Optimization . . . . 84
A.2. Implicit Mobility Management . . . . . . . . . . . . . . 84
A.3. Direct Underlying Interfaces . . . . . . . . . . . . . . 85
A.4. AERO Critical Infrastructure Considerations . . . . . . . 85
A.5. AERO Server Failure Implications . . . . . . . . . . . . 86
A.6. AERO Client / Server Architecture . . . . . . . . . . . . 86
Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 89
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 89
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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 a secure 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 original IP packets as single-hop neighbors via
encapsulation and fragmentation. The OMNI Adaptation Layer (OAL)
supports multilink operation for increased reliability, bandwidth
optimization and traffic path selection while performing
fragmentation and reassembly to accommodate Maximum Transmission Unit
(MTU) diversity.
The AERO service comprises Clients, Proxy/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 secure cloud-based service where mobile node Clients
may use any Proxy/Server acting as a Mobility Anchor Point (MAP) and
fixed nodes may use any Relay on the link for efficient
communications. Fixed nodes forward original IP packets destined to
other AERO nodes via the nearest Relay, which forwards them through
the cloud. A mobile node's initial packets are forwarded through the
Proxy/Server, and direct routing is supported through automatic
extended route optimization while 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 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 is the source of a route to the MSP, and
hence uplink traffic to the mobile node is naturally routed to the
nearest Relay.
AERO can be used with OMNI links that span private-use Internetworks
and/or public Internetworks such as the global Internet. In 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 as a secure aeronautical internetworking service
for both manned and unmanned aircraft, where the aircraft is treated
as a mobile node that can connect an Internet of Things (IoT). AERO
is also applicable to a wide variety of other use cases. For
example, it can be used to coordinate the links of mobile nodes
(e.g., cellphones, tablets, laptop computers, etc.) that connect into
a home enterprise network via public access networks 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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a control message service for coordinating neighbor relationships
between nodes connected to a common link. AERO uses the IPv6 ND
messaging service specified in [RFC4861].
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 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.
(OAL) carrier packet
an encapsulated OAL fragment following *NET encapsulation or prior
to *NET decapsulation. OAL sources and destinations exchange
carrier packets over underlying interfaces, and may be separated
by one or more OAL intermediate nodes. OAL intermediate nodes may
perform re-encapsulation on carrier packets by removing the *NET
headers of the first hop network and replacing them with new *NET
headers for the next hop network.
OAL source
an OMNI interface acts as an OAL source when it encapsulates
original IP packets to form OAL packets, then performs OAL
fragmentation and *NET encapsulation to create carrier packets.
OAL destination
an OMNI interface acts as an OAL destination when it decapsulates
carrier packets, then performs OAL reassembly and decapsulation to
derive the original IP packet.
OAL intermediate node
an OMNI interface acts as an OAL intermediate node when it removes
the *NET headers of carrier packets received on a first segment,
then re-encapsulates the carrier packets in new *NET headers and
forwards them into the next segment. OAL intermediate nodes
decrement the Hop Limit of the OAL IPv6 header during re-
encapsulation, and discard the packet if the Hop Limit reaches 0.
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)
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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)
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 Proxy/
Servers. The Client assigns an MNP-LLA to the OMNI interface for
use in ND exchanges with other AERO nodes and forwards original IP
packets to correspondents according to OMNI interface neighbor
cache state.
AERO Proxy/Server ("Proxy/Server")
a dual-function node that provides a proxying service between AERO
Clients and external peers on its Client-facing ANET interfaces
(i.e., in the same fashion as for an enterprise network proxy) as
well as default forwarding and Mobility Anchor Point (MAP)
services for coordination with correspondents on its INET-facing
interfaces. The Proxy/Server configures an OMNI interface and
assigns an ADM-LLA to support the operation of IPv6 ND services,
while advertising all of its associated MNPs via BGP peerings with
Bridges. Note that the Proxy and Server functions can be
considered logically separable, but since each Proxy/Server must
be informed of all of the Client's other multilink Proxy/Server
affiliations the AERO service is best supported when the two
functions are coresident on the same physical or logical platform.
AERO Relay ("Relay")
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a Proxy/Server that provides forwarding services between nodes
reached via the OMNI link and correspondents on connected
downstream links. AERO Relays configure an OMNI interface and
assign an ADM-LLA the same as Proxy/Servers. AERO Relays also run
a dynamic routing protocol to discover any non-MNP IP GUA routes
in service on its connected downstream network links. In both
cases, the Relay advertises the MSP(s) to its downstream networks,
and distributes all of its associated non-MNP IP GUA routes via
BGP peerings with Bridges (i.e., the same as for Proxy/Servers).
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 carrier packets between OMNI link segments as OAL
intermediate nodes while decrementing the OAL IPv6 header Hop
Limit but without decrementing the network layer IP TTL/Hop Limit.
AERO Bridges peer with Proxy/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.
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 original IP packet
presented to the OMNI interface.
end user network (EUN)
an internal virtual or external edge IP network that an AERO
Client or Relay connects to the rest of the network via the OMNI
interface. The Client/Relay sees each EUN as a "downstream"
network, and sees the OMNI interface as the point of attachment to
the "upstream" network.
Mobile Node (MN)
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an AERO Client and all of its downstream-attached networks that
move together as a single unit, i.e., an end system that connects
an Internet of Things.
Mobile Router (MR)
a MN's on-board router that forwards original IP packets between
any downstream-attached networks and the OMNI link. The MR is the
MN entity that hosts the AERO Client.
Route Optimization Source (ROS)
the AERO node nearest the source that initiates route
optimization. The ROS may be a Proxy/Server/Relay acting on
behalf of the source, or may be the source Client itself.
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 Proxy/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 Proxy/Servers
and Bridges that tracks all Proxy/Server-to-Client associations.
Mobility Service (MS)
the collective set of all Proxy/Servers, Bridges and Relays that
provide the AERO Service to Clients.
Mobility Service Endpoint MSE)
an individual Proxy/Server, Bridge or Relay in the Mobility
Service.
Throughout the document, the simple terms "Client", "Proxy/Server",
"Bridge" and "Relay" refer to "AERO Client", "AERO Proxy/Server",
"AERO Bridge" and "AERO Relay", respectively. Capitalization is used
to distinguish these terms from other common Internetworking uses in
which they appear without capitalization.
The terminology of 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
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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:
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, Proxy/
Servers and Relays are critical infrastructure elements in fixed
(i.e., non-mobile) INET deployments and hence have permanent and
unchanging INET addresses. Together, they constitute the AERO
service which provides an OMNI link virtual overlay for connecting
AERO Clients.
AERO Bridges 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 carrier 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 Proxy/
Servers and other Bridges in a dynamic routing protocol instance to
provide a Distributed Mobility Management (DMM) service for the list
of active MNPs (see Section 3.2.3). Bridges present the OMNI link as
a set of one or more Mobility Service Prefixes (MSPs) and configure
secured tunnels with Proxy/Servers, Relays and other Bridges; they
further maintain IP forwarding table entries for each MNP and any
other reachable non-MNP prefixes.
AERO Proxy/Servers in distributed INET locations provide default
forwarding and mobility/multilink services for AERO Client Mobile
Nodes (MNs). Each Proxy/Server also peers with Bridges in a dynamic
routing protocol instance to advertise its list of associated MNPs
(see Section 3.2.3). Proxy/Servers facilitate prefix delegation/
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registration exchanges with Clients, where each delegated prefix
becomes an MNP taken from an MSP. Proxy/Servers forward carrier
packets between OMNI interface neighbors and track each Client's
mobility profiles. Proxy/Servers provide a conduit for ANET Clients
to associate with additional Proxy/Servers in external INETs. The
Proxy forwards original IP packets between Clients and the OMNI link
according to forwarding information in the neighbor cache.
AERO Relays are Proxy/Servers that provide forwarding services to
exchange original IP packets 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
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:
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+----------------+
| AERO Bridge B1 |
| Nbr: S1, S2, P1|
|(X1->S1; X2->S2)|
| MSP M1 |
+-+------------+-+
+--------------+ | Secured | +--------------+
| AERO P/S S1 | | tunnels | | AERO P/S S2 |
| Nbr: C1, B1 +-----+ +-----+ Nbr: C2, B1 |
| default->B1 | | default->B1 |
| X1->C1 | | X2->C2 |
+-------+------+ +------+-------+
| OMNI link |
X===+===+======================================+===+===X
| |
+-----+--------+ +--------+-----+
|AERO Client C1| |AERO Client C2|
| Nbr: S1 | | Nbr: S2 |
| default->S1 | | default->S2 |
| MNP X1 | | MNP X2 |
+------+-------+ +-----+--------+
| |
.-. .-.
,-( _)-. ,-( _)-.
.-(_ IP )-. +-------+ +-------+ .-(_ IP )-.
(__ EUN )--|Host H1| |Host H2|--(__ EUN )
`-(______)-' +-------+ +-------+ `-(______)-'
Figure 1: AERO/OMNI Reference Model
In this model:
o the OMNI link is an overlay network service configured over one or
more underlying *NET partitions which may be managed by different
administrative authorities and have incompatible protocols and/or
addressing plans.
o AERO Bridge B1 aggregates Mobility Service Prefix (MSP) M1,
discovers Mobile Network Prefixes (MNPs) X* and advertises the MSP
via BGP peerings over secured tunnels to Proxy/Servers (S1, S2).
Bridges connect the disjoint segments of a partitioned OMNI link.
o AERO Proxy/Servers S1 and S2 configure secured tunnels with Bridge
B1 and also provide mobility, multilink, multicast and default
router services for their associated Clients C1 and C2.
o AERO Clients C1 and C2 associate with Proxy/Servers S1 and S2,
respectively. They receive Mobile Network Prefix (MNP)
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delegations X1 and X2, and also act as default routers for their
associated physical or internal virtual EUNs. Simple hosts H1 and
H2 attach to the EUNs served by Clients C1 and C2, respectively.
An OMNI link configured over a single *NET appears as a single
unified link with a consistent underlying network addressing plan.
In that case, all nodes on the link can exchange carrier 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 carrier packets directly with correspondents in
the same segment, and not with those in other segments. The only
means for joining the segments therefore is through inter-domain
peerings between AERO Bridges.
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)
[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:
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. . . . . . . . . . . . . . . . . . . . . . .
. .
. .-(::::::::) .
. .-(::::::::::::)-. +-+ .
. (:::: Segment A :::)--|B|---+ .
. `-(::::::::::::)-' +-+ | .
. `-(::::::)-' | .
. | .
. .-(::::::::) | .
. .-(::::::::::::)-. +-+ | .
. (:::: Segment B :::)--|B|---+ .
. `-(::::::::::::)-' +-+ | .
. `-(::::::)-' | .
. | .
. .-(::::::::) | .
. .-(::::::::::::)-. +-+ | .
. (:::: Segment C :::)--|B|---+ .
. `-(::::::::::::)-' +-+ | .
. `-(::::::)-' | .
. | .
. ..(etc).. x .
. .
. .
. <- OMNI link Bridged by encapsulation -> .
. . . . . . . . . . . . . .. . . . . . . . .
Figure 2: Bridging OMNI Link Segments
Bridges, Proxy/Servers and Relays 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 carrier packets in a flow. Route optimization can
then be employed to cause carrier 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
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
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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, MNPs and non-MNP routes 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 Proxy/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 Proxy/Servers and does not interact with either the public
Internet BGP routing system or any underlying INET routing systems.
In a reference deployment, each Proxy/Server is configured as an
Autonomous System Border Router (ASBR) for a stub Autonomous System
(AS) using a 32-bit AS Number (ASN) [RFC4271] that is unique within
the BGP instance, and each Proxy/Server further uses eBGP to peer
with one or more Bridges but does not peer with other Proxy/Servers.
Each *NET of a multi-segment OMNI link must include one or more
Bridges, which peer with the Proxy/Servers 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 routes currently in
service. The Bridges of different *NETs peer with one another using
eBGP.
Bridges maintain forwarding table entries only for the ULAs
corresponding to MNP and non-MNP routes that are currently active,
and carrier packets destined to all other ULAs will correctly incur
Destination Unreachable messages due to the black-hole route. In
this way, Proxy/Servers and Relays have only partial topology
knowledge (i.e., they know only about the routes their directly
associated Clients and non-AERO links) and they forward all other
carrier packets to Bridges which have full topology knowledge.
Each OMNI link segment assigns a unique ADM-ULA sub-prefix of
[ULA*]::/96. For example, a first segment could assign
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[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 Proxy/Servers and Relays that provide service for their
corresponding MNPs. For example, if three Proxy/Servers ('D', 'E'
and 'F') service the MNPs 2001:db8:1000:2000::/56,
2001:db8:3000:4000::/56 and 2001:db8:5000:6000::/56 then the routing
system would include:
D: [ULA*]:2001:db8:1000:2000/120
E: [ULA*]:2001:db8:3000:4000/120
F: [ULA*]:2001:db8:5000:6000/120
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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 messages 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).
o Segments Left is omitted, and replaced by a 5-bit SRT and 3-bit
FMT field.
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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 Proxy/Server
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;
otherwise, L2ADDR will contain the native *NET information of the
target itself.
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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), sets the Traffic Class, Flow Label, Hop
Limit and Payload Length as discussed in
[I-D.templin-6man-omni-interface], then finally 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" OAL fragment even if no actual fragmentation was
required.) The OAL source finally encapsulates each resulting OAL
fragment in an *NET header to form an OAL carrier 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 carrier 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Original IP Header |
| (first-fragment only) |
| src = 2001:db8:1:2::1 |
| dst = 2001:db8:1234:5678::1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ ~
~ Original Packet Body/Fragment ~
~ ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: Carrier Packet Format
In this format, the original 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 carrier
packets, they are forwarded over possibly multiple OAL intermediate
nodes in the OMNI link spanning tree 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 carrier packets
over the spanning tree instead of network-layer routing according to
MNP routes. As a result, opportunities for 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 Proxy/Servers or
Relays can be addressed without being subject to mobility events.
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Conversely, only the first few carrier packets destined to Clients
need to 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 original 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 original IP 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
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independent overlay instances. A communication failure in one
instance therefore will not affect communications in other instances.
Each SRT is identified by a distinct value in bits 48-63 of
[ULA]::/48, i.e., as [ULA0]::/64, [ULA1]::/64, [ULA2]::/64, etc.
Each OMNI interface is identified by a unique interface name (e.g.,
omni0, omni1, omni2, etc.) and assigns an 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 an
original IPv6 packet will traverse when there may be multiple
alternatives.
When the AERO node processes the SRH and forwards the original IPv6
packet to the correct OMNI interface, the OMNI interface writes the
next IPv6 address from the SRH into the IPv6 destination address and
decrements Segments Left. If decrementing would cause Segments Left
to become 0, the OMNI interface deletes the SRH before forwarding.
This form of Segment Routing supports Safety-Based Multilink (SBM).
3.2.7. 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 carrier 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
carrier packets to a Bridge.
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When a Bridge receives a carrier 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
the ORH from the carrier packet. The Bridge then writes the MNP-ULA
corresponding to the ORH Destination Suffix into the OAL destination
address, decrements the OAL IPv6 header Hop Limit (and discards the
packet if the Hop Limit reaches 0), re-encapsulates the carrier
packet according to L2ADDR and forwards the carrier packet either to
the LHS Proxy/Server 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 more NATs. Native INET interfaces have global IP addresses
that are reachable from any INET correspondent. The INET-facing
interfaces of Proxy/Servers are native interfaces, as are Relay
and Bridge interfaces. NATed INET interfaces connect to a private
network behind one or more NATs 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 carrier packets
flowing.
o ANET interfaces connect to an ANET that is separated from the open
INET by a Proxy/Server. Proxy/Servers 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 Proxy/
Server. Other than the link-layer encapsulation format, VPNed
interfaces behave the same as Direct interfaces.
o Direct (i.e., single-hop point-to-point) interfaces connect a
Client directly to a Proxy/Server without crossing any ANET/INET
paths. An example is a line-of-sight link between a remote pilot
and an unmanned aircraft. The same Client considerations apply as
for VPNed interfaces.
OMNI interfaces use OAL encapsulation and fragmentation as discussed
in Section 3.2.4. OMNI interfaces use *NET encapsulation (see:
Section 3.6) to exchange carrier packets with OMNI link neighbors
over INET or VPNed interfaces as well as over ANET interfaces for
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which the Client and Proxy/Server may be multiple IP hops away. OMNI
interfaces do not use link-layer encapsulation over Direct underlying
interfaces or ANET interfaces when the Client and Proxy/Server are
known to be on the same underlying link.
OMNI interfaces maintain a neighbor cache for tracking per-neighbor
state the same as for any interface. OMNI interfaces use 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 and Proxy/Server 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
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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
carrier packets to the underlying secured tunnel interface. Routing
protocols such as BGP that run over the OMNI interface do not employ
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 Proxy/Servers and Clients configure OMNI interfaces as their
point of attachment to the OMNI link. AERO nodes assign the MSPs for
the link to their OMNI interfaces (i.e., as a "route-to-interface")
to ensure that original IP packets with destination addresses covered
by an MNP not explicitly assigned to a non-OMNI interface are
directed to the OMNI interface.
OMNI interface initialization procedures for Proxy/Servers, Clients
and Bridges are discussed in the following sections.
3.4.1. AERO Proxy/Server and Relay Behavior
When a Proxy/Server enables an OMNI interface, it assigns an
ADM-{LLA,ULA} appropriate for the given OMNI link segment. The
Proxy/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 includes one or more secured tunnels as well as
an NBMA nexus as underlying interfaces for sending carrier packets to
OMNI interface neighbors. The Proxy/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 Proxy/Servers that run a dynamic routing protocol
to redistribute routes between the OMNI interface and INET/EUN
interfaces (see: Section 3.2.3). The Relay provisions MNPs to
networks on the INET/EUN interfaces (i.e., the same as a Client would
do) and advertises the MSP(s) for the OMNI link over the INET/EUN
interfaces. The Relay further provides an attachment point of the
OMNI link to a non-MNP-based global topology.
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3.4.2. AERO Client Behavior
When a Client enables an OMNI interface, it assigns either an
MNP-{LLA, ULA} or a Temporary ULA and sends RS messages with ND
parameters over its underlying interfaces to a Proxy/Server, which
returns an RA message with corresponding parameters. The RS/RA
messages may pass 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 Proxy/Server and begin
using these new addresses. If the Client is operating outside the
context of AERO infrastructure such as in a Mobile Ad-hoc Network
(MANET), however, it may continue using Temporary ULAs for Client-to-
Client communications until it encounters an infrastructure element
that can provide an MNP.)
3.4.3. 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 Proxy/Servers 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]. In addition to ordinary neighbor cache entries,
Proxy neighbor cache entries are created and maintained by AERO
Proxy/Servers when they proxy Client ND message exchanges [RFC4389].
AERO Proxy/Servers maintain proxy neighbor cache entries for each of
their associated Clients.
To the list of neighbor cache entry states in Section 7.3.2 of
[RFC4861], Proxy/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, the Proxy/Server forwards
carrier packets destined to the target Client to the Client's new
location instead. 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) to allow a window for carrier packets in flight to be
delivered while stale route optimization state may be present.
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Proxy/Servers can act as RORs on behalf of 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. When a Proxy/Server ROR receives an authentic
NS message used for route optimization, it first searches for a proxy
neighbor cache entry for the target Client and accepts the message
only if there is an entry. The Proxy/Server (or the actual target
Client acting as an ROR) then returns a solicited NA message while
creating a neighbor cache entry for the ROS and caching the
Identification value found in the NS message carrier packet as the
starting window Identification value for this ROS. Proxy/Servers
acting as proxy RORs also create or update a "Report List" entry for
the ROS in the target Client's proxy neighbor cache entry with a
"ReportTime" variable set 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
carrier packets can be forwarded directly to the target, i.e.,
instead of via a default route. The ROS also maintains a window
start Identification value that is monotonically incremented for each
OAL packet sent to this target, and sets new window start
Identification values when it sends a new NS. 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
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configure the same values. Most importantly, DEPART_TIME and
REPORT_TIME SHOULD be set to a value that is sufficiently longer than
REACHABLE_TIME to avoid packet loss due to stale route optimization
state.
3.5.1. OMNI 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
returned by a Proxy/Server ROR and set to 1 for all other
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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.
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
[I-D.templin-6man-omni-interface] while including an ORH if necessary
as specified in Section 3.2.4. OAL encapsulation produces OAL
packets, while OAL fragmentation turns them into OAL fragments which
are then encapsulated in *NET headers as carrier packets.
For carrier packets undergoing re-encapsulation at an OAL
intermediate node, the OMNI interface decrements the OAL IPv6 header
Hop Limit and discards the carrier packet if the Hop Limit reaches 0.
The intermediate node next removes the *NET encapsulation headers
from the first segment and re-encapsulates the packet in new *NET
encapsulation headers for the next segment.
When a Proxy/Server or Relay re-encapsulates a carrier 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 original IP packet was received on.
When carrier packets containing OAL fragments arrive, the OMNI
interface reassembles as discussed in Section 3.9.
3.8. OMNI Interface Data Origin Authentication
AERO nodes employ simple data origin authentication procedures. In
particular:
o AERO Bridges and Proxy/Servers accept carrier packets (including
either data or control messages) received from the (secured)
spanning tree.
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o AERO Proxy/Servers and Clients accept carrier packets and original
IP packets that originate from within the same secured ANET.
o AERO Clients and Relays accept original IP packets from downstream
network correspondents based on ingress filtering.
o AERO Clients, Relays and Proxy/Servers verify carrier packet UDP/
IP encapsulation addresses according to [RFC4380].
o AERO Clients (as well as Proxy/Servers and Relays when acting 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 original IP
packet if necessary. When the network layer presents the OMNI
interface with multiple original IP packets bound to the same OAL
destination, the OAL source can concatenate them together into a
single OAL super-packet as discussed in
[I-D.templin-6man-omni-interface]. The OAL source then fragments the
OAL 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 first fragment. The OAL source then
encapsulates each OAL fragment in *NET headers for transmission as
carrier packets 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]).
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Note: A Client that does not (yet) have neighbor cache state for a
target may omit the ORH in carrier 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. 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 carrier packets enter from the link layer (i.e., from
an OMNI interface neighbor). All original IP packets and carrier
packets entering a node's OMNI interface first undergo data origin
authentication as discussed in Section 3.8. Those that satisfy data
origin authentication are processed further, while all others are
dropped silently.
Original IP packets that enter the OMNI interface from the network
layer are forwarded to an OMNI interface neighbor using OAL
encapsulation and fragmentation to produce carrier packets for
transmission over underlying interfaces. (If routing indicates that
the original IP packet should instead be forwarded back to the
network layer, the packet is dropped to avoid looping). Carrier
packets that enter the OMNI interface from the link layer are either
re-encapsulated and re-admitted into the OMNI link, or reassembled
and forwarded to the network layer where they are subject to either
local delivery or IP forwarding. In all cases, the OAL MUST NOT
decrement the 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
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.
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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, Proxy/Servers and Bridges. In the following
discussion, an original IP packet's destination address is said to
"match" if it is the same as a cached address, or if it is covered by
a cached prefix (which may be encoded in an MNP-LLA).
3.10.1. Client Forwarding Algorithm
When an original IP packet enters a Client's OMNI interface from the
network layer the Client searches for a 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 original IP packet toward a Proxy/Server. 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 carrier
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
carrier 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 carrier packets
to its Proxy/Server and initiates NAT traversal procedures. If the
Client's intended source underlying interface is also behind a NAT
and located 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).
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The Client next sends an NS(NUD) message toward the MNP-ULA of the
neighbor via its Proxy/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 carrier packets directly to the L2ADDR information for the
neighbor instead of indirectly via the Proxy/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
carrier packets are still flowing.
When an carrier 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 original IP packet to the
network layer. Otherwise, the Client drops the original IP packet
and MAY return a network-layer ICMP Destination Unreachable message
subject to rate limiting (see: Section 3.11).
Note: Clients and their Proxy/Server (and other Client) peers can
exchange original IP packets over ANET underlying interfaces without
invoking the OAL, since the ANET is secured at the link and physical
layers. By forwarding original IP packets without invoking the OAL,
however, the ANET peers can engage only in classical path MTU
discovery since the packets are subject to loss and/or corruption due
to the various per-link MTU limitations that may occur within the
ANET. Moreover, the original IP packets do not include per-packet
Identification values that can be used for data origin authentication
and link-layer retransmission purposes, nor the OAL integrity check.
The tradeoff therefore involves an assessment of the per-packet
encapsulation overhead saved by bypassing the OAL vs. inheritance of
classical network "brittleness".
3.10.2. Proxy/Server Forwarding Algorithm
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 carrier packets with OAL destination set to its own ADM-
ULA. When the Proxy/Server receives carrier packets on underlying
interfaces with OAL destination set to its own ADM-ULA, it performs
OAL reassembly if necessary to obtain the original IP packet.
The Proxy/Server 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 packet 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 carrier
packets to a Bridge; otherwise, it forwards the carrier packets
directly to the neighbor. If the neighbor is behind a NAT, the
Proxy/Server instead forwards initial carrier packets via a Bridge
while sending an NS(NUD) to the neighbor. When the Proxy/Server
receives the NA(NUD), it can begin forwarding carrier 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 presents the original IP
packet 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 carrier packet with OAL destination
set to a non-MNP ULA, it accepts the carrier 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 carrier 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 carrier packet with OAL destination
set to an MNP-ULA, it accepts the carrier 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 Proxy/Server, then re-encapsulates the carrier
packet and forwards it to a Bridge which will eventually deliver it
to the new Proxy/Server.
If the neighbor cache state 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
the Client which then must reassemble. In the former case, the
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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
carrier packet containing an OAL first fragment.
Note: Clients and their Proxy/Server peers can exchange original IP
packets over ANET underlying interfaces without invoking the OAL,
since the ANET is secured at the link and physical layers. By
forwarding original IP packets without invoking the OAL, however, the
Client and Proxy/Server can engage only in classical path MTU
discovery since the packets are subject to loss and/or corruption due
to the various per-link MTU limitations that may occur within the
ANET. Moreover, the original IP packets do not include per-packet
Identification values that can be used for data origin authentication
and link-layer retransmission purposes, nor the OAL integrity check.
The tradeoff therefore involves an assessment of the per-packet
encapsulation overhead saved by bypassing the OAL vs. inheritance of
classical network "brittleness".
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 carrier packets the same as any IPv6 router. Bridges
convey carrier packets and original IP packets that encapsulate IPv6
ND control messages or routing protocol control messages using
security encapsulations, and may convey packets that encapsulate
ordinary data without including security encapsulations. When the
Bridge receives a carrier packet or an original IP packet, 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 packet is a carrier packet with a destination that matches
its ADM-ULA Subnet Router Anycast address the Bridge processes the
carrier packet locally before forwarding. The Bridge drops the
carrier packet if it 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. The Bridge next examines the ORH FMT code. If the code
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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 carrier packet
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 carrier
packet to the ADM-ULA Proxy/Server while invoking NAT traversal
procedures the same as for Proxy/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 packet is a carrier packet with a destination that
matches a forwarding table entry the Bridge forwards the carrier
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, if the packet is an original IP packet with a destination
that matches one of the Bridge's own addresses, the Bridge submits
the original IP packet for local delivery to support local
applications such as routing protocols.
o else, the Bridge drops the packet and returns an ICMP Destination
Unreachable as above.
As for any IP router, the Bridge decrements the OAL IPv6 header Hop
Limit when it forwards the carrier packet and drops the packet if the
Hop Limit reaches 0. 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 original IP packet header. Bridges do not insert OAL/
ORH headers themselves; instead, they act as IPv6 routers and forward
carrier packets based on their destination addresses.
Bridges forward packets received from a first segment without
security encapsulations to the next segment also without including
security encapsulations. Bridges forward packets received from a
first segment with security encapsulations to the next segment also
including security encapsulations. Bridges use a single IPv6 routing
table that always determines the same next hop for a given OAL
destination whether or not security encapsulation is included.
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3.11. OMNI Interface Error Handling
When an AERO node admits an original IP packet into the OMNI
interface, it may receive link-layer or network-layer error
indications.
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 carrier 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 original IP
packet that generated the error, also known as the "packet-in-error".
For ICMPv6, [RFC4443] specifies that the packet-in-error includes:
"As much of invoking packet as possible without the ICMPv6 packet
exceeding the minimum IPv6 MTU" (i.e., no more than 1280 bytes). For
ICMPv4, [RFC0792] specifies that the packet-in-error includes:
"Internet Header + 64 bits of Original Data Datagram", however
[RFC1812] Section 4.3.2.3 updates this specification by stating: "the
ICMP datagram SHOULD contain as much of the original datagram as
possible without the length of the ICMP datagram exceeding 576
bytes".
The link-layer error message format is shown in Figure 5 (where, "L2"
and "L3" refer to link-layer and network-layer, respectively):
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
| L2 IP Header of |
| error message |
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| L2 ICMP Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ---
~ ~ P
| IP and other encapsulation | a
| headers of original IP packet | c
~ ~ k
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ e
~ ~ t
| IP header of |
| original IP packet | i
~ ~ n
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~ e
| Upper layer headers and | r
| leading portion of body | r
| of the original IP 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 carrier packets that it sends
to one of its neighbor correspondents, the node should process the
message as an indication that a path may be failing, and
optionally initiate NUD over that path. If it receives
Destination Unreachable messages over multiple paths, the node
should allow future carrier packets destined to the correspondent
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to flow through a default route and re-initiate route
optimization.
o When an AERO Client receives persistent link-layer Destination
Unreachable messages in response to carrier packets that it sends
to one of its neighbor Proxy/Servers, the Client should mark the
path as unusable and use another path. If it receives Destination
Unreachable messages on many or all paths, the Client should
associate with a new Proxy/Server and release its association with
the old Proxy/Server as specified in Section 3.16.5.
o When an AERO Proxy/Server receives persistent link-layer
Destination Unreachable messages in response to carrier packets
that it sends to one of its neighbor Clients, the Proxy/Server
should mark the underlying path as unusable and use another
underlying path.
o When an AERO Proxy/Server receives link-layer Destination
Unreachable messages in response to a carrier packet that it sends
to one of its permanent neighbors, it treats the messages as an
indication that the path to the neighbor may be failing. However,
the dynamic routing protocol should soon reconverge and correct
the temporary outage.
When an AERO Bridge receives a carrier packet for which the network-
layer destination address is covered by an MSP, 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 IP 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 a carrier 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 IP 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 Proxy/Server on the OMNI link is configured to facilitate
Client prefix delegation/registration requests. Each Proxy/Server is
provisioned with a database of MNP-to-Client ID mappings for all
Clients enrolled in the AERO service, as well as any information
necessary to authenticate each Client. The Client database is
maintained by a central administrative authority for the OMNI link
and securely distributed to all Proxy/Servers, e.g., via the
Lightweight Directory Access Protocol (LDAP) [RFC4511], via static
configuration, etc. Clients receive the same service regardless of
the Proxy/Servers they select.
AERO Clients and Proxy/Servers use ND messages to maintain neighbor
cache entries. AERO Proxy/Servers configure their OMNI interfaces as
advertising NBMA interfaces, and therefore send unicast RA messages
with a short Router Lifetime value (e.g., ReachableTime seconds) in
response to a Client's RS message. Thereafter, Clients send
additional RS messages to keep Proxy/Server state alive.
AERO Clients and Proxy/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 Proxy/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 Proxy/
Server accepts the Client's MNP assertion, it injects the MNP into
the routing system and establishes the necessary neighbor cache
state. If the Client does not have a pre-assigned MNP, it can
instead employ prefix delegation by including the unspecified address
(::) as the source address of an RS message and with an OMNI option
with prefix delegation parameters to request an MNP.
The following sections specify the Client and Proxy/Server behavior.
3.12.2. AERO Client Behavior
AERO Clients discover the addresses of Proxy/Servers in a similar
manner as described in [RFC5214]. Discovery methods include static
configuration (e.g., from a flat-file map of Proxy/Server addresses
and locations), or through an automated means such as Domain Name
System (DNS) name resolution [RFC1035]. Alternatively, the Client
can discover Proxy/Server addresses through a layer 2 data link login
exchange, or through 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 Proxy/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 them to correlate RA replies. If the
Client already knows the Proxy/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.
For INET Clients, the Client must ensure that the RS message is no
larger than the minimum/path MPS for the chosen Proxy/Server and must
include a security signature that the Proxy/Server can verify. The
Client next applies OAL encapsulation such that the entire RS message
fits within an OAL First Fragment (i.e., as an atomic fragment) while
including an Identification number that will serve as the window
start Identification value for future packets it will send via this
Proxy/Server.
The Client then sends the RS message (either directly via Direct
interfaces, via a VPN for VPNed interfaces, via an access router for
ANET interfaces or via INET encapsulation for INET interfaces) 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 attempts through the first Proxy/Server
and try another Proxy/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 Proxy/
Server's ADM-LLA as the network-layer address and the Proxy/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 Proxy/Server has
committed to maintaining the MNP in the routing system via this
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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
Proxy/Server by sending RS messages via each additional interface as
described above. The RS messages include the same parameters as for
the initial RS/RA exchange, but with destination address set to the
Proxy/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 Proxy/Server's RA response,
it has assurance that the Proxy/Server has been updated with the new
information.
If the Client wishes to discontinue use of a Proxy/Server it issues
an RS message over any underlying interface with an OMNI option with
a prefix release indication. When the Proxy/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 Proxy/Server
withdraws the MNP from the routing system.
3.12.3. AERO Proxy/Server Behavior
AERO Proxy/Servers act as IP routers and support a prefix delegation/
registration service for Clients. Proxy/Servers arrange to add their
ADM-LLAs to a static map of Proxy/Server addresses for the link and/
or the DNS resource records for the FQDN
"linkupnetworks.[domainname]" before entering service. Proxy/Server
addresses should be geographically and/or topologically referenced,
and made available for discovery by Clients on the OMNI link.
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When a Proxy/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 Proxy/Server performs OAL
reassembly and decapsulation, then authenticates the RS message and
processes the prefix delegation/registration parameters. The Proxy/
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 Proxy/Server returns the MNPs, it also creates a
forwarding table 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 Proxy/Server creates an IPv6
forwarding table entry for each MNP. For IPv4, the Proxy/Server
creates an IPv6 forwarding table entry with the IPv4-compatibility
MNP-ULA prefix corresponding to the IPv4 address.
The Proxy/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 Proxy/
Server updates the neighbor cache entry by recording the information
in each Interface Attributes sub-option in the RS OMNI option. The
Proxy/Server also records the actual OAL/INET addresses in the
neighbor cache entry. For INET Clients, the Proxy/Server also
records the RS carrier packet Identification number which will serve
as the window start Identification value for future packets it will
receive from this Client.
Next, the Proxy/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
Proxy/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 Proxy/Server also sets Cur Hop Limit, M
and O flags, Reachable Time and Retrans Timer to values appropriate
for the OMNI link. The Proxy/Server includes the MNPs, any other
prefix management parameters and an OMNI option with no Interface
Attributes but with an Origin Indication sub-option per
[I-D.templin-6man-omni-interface] with the mapped and obfuscated Port
Number and IP address corresponding to the Client's own INET address
in the case of INET Clients or to the Proxy/Server's INET-facing
address for all other Clients. The Proxy/Server then includes one or
more RIOs that encode the MSPs for the OMNI link, plus an MTU option
(see Section 3.9). The Proxy/Server finally forwards the message to
the Client using OAL encapsulation/fragmentation as necessary.
After the initial RS/RA exchange, the Proxy/Server maintains a
ReachableTime timer for each of the Client's underlying interfaces
individually (and for the Client's neighbor cache entry collectively)
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set to expire after ReachableTime seconds. If the Client (or Proxy)
issues additional RS messages, the Proxy/Server sends an RA response
and resets ReachableTime. If the Proxy/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 Proxy/Server marks the interface as DOWN. If
ReachableTime expires before any new RS is received on any individual
underlying interface, the Proxy/Server sets the neighbor cache entry
state to STALE and sets a 10 second timer. If the Proxy/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 Proxy/Server processes any ND messages pertaining to the Client
and returns an NA/RA reply in response to solicitations. The Proxy/
Server may also issue unsolicited RA messages, e.g., with reconfigure
parameters to cause the Client to renegotiate its prefix delegation/
registrations, with Router Lifetime set to 0 if it can no longer
service this Client, etc. Finally, If the neighbor cache entry is in
the DEPARTED state, the Proxy/Server deletes the entry after
DepartTime expires.
Note: Clients SHOULD notify former Proxy/Servers of their departures,
but Proxy/Servers are responsible for expiring neighbor cache entries
and withdrawing routes even if no departure notification is received
(e.g., if the Client leaves the network unexpectedly). Proxy/Servers
SHOULD therefore set Router Lifetime to ReachableTime seconds in
solicited RA messages to minimize persistent stale cache information
in the absence of Client departure notifications. A short Router
Lifetime also ensures that proactive RS/RA messaging between Clients
and Proxy/Servers will keep any NAT state alive (see above).
Note: All Proxy/Servers on an OMNI link MUST advertise consistent
values in the RA Cur Hop Limit, M and O flags, Reachable Time and
Retrans Timer fields the same as for any link, since unpredictable
behavior could result if different Proxy/Servers on the same link
advertised different values.
3.12.3.1. DHCPv6-Based Prefix Registration
When a Client is not pre-provisioned with an MNP-LLA, it will need
for the Proxy/Server to select one or more MNPs on its behalf and set
up the correct state in the AERO routing service. (A Client with a
pre-provisioned MNP may also request the Proxy/Server to select
additional MNPs.) The DHCPv6 service [RFC8415] is used to support
this requirement.
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When a Client needs to have the Proxy/Server select MNPs, it sends an
RS message with source address set to the unspecified address (::)
and with an OMNI option that includes a DHCPv6 message sub-option
with DHCPv6 Prefix Delegation (DHCPv6-PD) parameters. When the
Proxy/Server receives the RS message, it extracts the DHCPv6-PD
message from the OMNI option.
The Proxy/Server then acts as a "Proxy DHCPv6 Client" in a message
exchange with the locally-resident DHCPv6 server, which delegates
MNPs and returns a DHCPv6-PD Reply message. (If the Proxy/Server
wishes to defer creation of MN state until the DHCPv6-PD Reply is
received, it can instead act as a Lightweight DHCPv6 Relay Agent per
[RFC6221] by encapsulating the DHCPv6-PD message in a Relay-forward/
reply exchange with Relay Message and Interface ID options.)
When the Proxy/Server receives the DHCPv6-PD Reply, it adds a route
to the routing system and creates an MNP-LLA based on the delegated
MNP. The Proxy/Server then sends an RA back to the Client with the
(newly-created) MNP-LLA as the destination address and with the
DHCPv6-PD Reply message 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 Proxy/
Server receives the RS message, it forwards a self-generated DHCPv6
Solicit message to the DHCPv6 server on behalf of the Client. When
the Proxy/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 Function
Clients connect to the OMNI link via Proxy/Servers, with one Proxy/
Server for each underlying interface. Each of the Client's Proxy/
Servers must be informed of all of the Client's additional underlying
interfaces. For Clients on Direct and VPNed underlying interfaces
the Proxy/Server "A" for that interface is directly connected, for
Clients on ANET underlying interfaces Proxy/Server "A" is located on
the ANET/INET boundary, and for Clients on INET underlying interfaces
Proxy/Server "A" is located somewhere in the connected Internetwork.
When the Client registers with Proxy/Server "A", it must also report
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the registration to any other Proxy/Servers for other underlying
interfaces "B", "C", "D", etc. for which an underlying interface
relationship has already been established. The Proxy/Server
satisfies these requirements as follows:
o when Proxy/Server "A" receives an RS message from a new Client, it
first authenticates the message then examines the network-layer
destination address. If the destination address is Proxy/Server
"A"'s ADM-LLA or (link-local) All-Routers multicast, Proxy/Server
"A" creates a proxy neighbor cache entry and caches the Client
link-layer addresses along with the OMNI option information and
any other identifying information including OAL Identification
values, Client Identifiers, Nonce values, etc. If the RS message
destination was the ADM-LLA of a different Proxy/Server "B" (or,
if the OMNI option included an MS-Register sub-option with the
ADM-LLA of a different Proxy/Server "B"), Proxy/Server "A"
encapsulates a proxyed version of the RS message in an OAL header
with source set to Proxy/Server "A"'s ADM-ULA and destination set
to Proxy/Server "B"'s ADM-ULA. Proxy/Server "A" also includes an
OMNI header with an Interface Attributes option that includes its
own INET address plus a unique UDP Port Number for this Client,
then forwards the message into the OMNI link spanning tree.
(Note: including a unique Port Number allows Proxy/Server "B" to
distinguish different Clients located behind the same Proxy/Server
"A" at the link-layer, whereas the link-layer addresses would
otherwise be indistinguishable.)
o when the Proxy/Server "B" receives the RS, it authenticates the
message then creates or updates a neighbor cache entry for the
Client with Proxy/Server "A"'s ADM-ULA, INET address and UDP Port
Number as the link-layer address information. Proxy/Server "B"
then sends an RA message back to Proxy/Server "A" via the spanning
tree.
o when Proxy/Server "A" receives the RA, it authenticates the
message and matches it with the proxy neighbor cache entry created
by the RS. Proxy/Server "A" then caches the prefix information as
a mapping from the Client's MNPs to the Client's link-layer
address, caches the Proxy/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.
o The Client repeats this process with each Proxy/Server "B", "C",
"D" for each of its additional underlying interfaces.
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After the initial RS/RA exchanges each Proxy/Server forwards any of
the Client's carrier 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/Server instead forwards any carrier packets
destined to a neighbor cache target directly to the target according
to the OAL/link-layer information - the process of establishing
neighbor cache entries is specified in Section 3.14.
While the Client is still associated with each Proxy/Server "A", "A"
can send NS, RS and/or unsolicited NA messages to update the neighbor
cache entries of other AERO nodes 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 any Proxy/Server "B", "C", "D" ceases to send solicited
advertisements, Proxy/Server "A" sends unsolicited RAs to the Client
with destination set to (link-local) All-Nodes multicast and with
Router Lifetime set to zero to inform Clients that a Proxy/Server has
failed. Although Proxy/Server "A" can engage 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 "A" to convey QoS
changes, etc. The ND messages sent by the Client include the
Client's MNP-LLA as the source in order to differentiate them from
the ND messages sent by Proxy/Server "A".
If the Client becomes unreachable over an underlying interface,
Proxy/Server "A" sets the neighbor cache entry state to DEPARTED and
retains the entry for DepartTime seconds. While the state is
DEPARTED, Proxy/Server "A" forwards any carrier packets destined to
the Client to a Bridge via OAL/ORH encapsulation. When DepartTime
expires, Proxy/Server "A" deletes the neighbor cache entry and
discards any further carrier packets destined to this (now forgotten)
Client.
In some ANETs that employ a Proxy/Server, the Client's MNP can be
injected into the ANET routing system. In that case, the Client can
send original IP packets without invoking the OAL so that the ANET
routing system transports the original IP packets to the Proxy. 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 ANET first-hop access router is on the same underlying link as
the Client and recognizes the AERO/OMNI protocol, the Client can
avoid OAL encapsulation for both its control and data messages. When
the Client connects to the link, it can send an unencapsulated RS
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message with source address set to its own MNP-LLA (or to a Temporary
LLA), and with destination address set to the ADM-LLA of the Client's
selected Proxy/Server or to (link-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 ANET access router then performs OAL encapsulation on the RS
message and forwards it to a Proxy/Server at the ANET/INET boundary.
When the access router and Proxy/Server are one and the same node,
the Proxy/Server would share and underlying link with the Client but
its message exchanges with outside correspondents would need to pass
through a security gateway at the ANET/INET border. The method for
deploying access routers and Proxys (i.e. as a single node or
multiple nodes) is an ANET-local administrative consideration.
Note: The Proxy/Server can apply packing as discussed in
[I-D.templin-6man-omni-interface] if an opportunity arises to
concatenate multiple original IP packets that will be destined to the
same neighbor.
3.13.1. Detecting and Responding to Proxy/Server Failures
In environments where fast recovery from Proxy/Server failure is
required, Proxy/Server "A" SHOULD use proactive Neighbor
Unreachability Detection (NUD) to track peer Proxy/Server "B"
reachability in a similar fashion as for Bidirectional Forwarding
Detection (BFD) [RFC5880]. Proxy/Server "A" 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.
Proxy/Server "A" performs proactive NUD with peer Proxy/Server "B"
for which there are currently active Clients by sending continuous NS
messages in rapid succession, e.g., one message per second. Proxy/
Server "A" sends the NS message via the spanning tree with its own
ADM-LLA as the source and the ADM-LLA of the peer Proxy/Server "B" as
the destination. When Proxy/Server "A" is also sending RS messages
to the peer Proxy/Server "B" on behalf of ANET Clients, the resulting
RA responses can be considered as equivalent hints of forward
progress. This means that Proxy/Server "B" need not also send a
periodic NS if it has already sent an RS within the same period. If
the peer Proxy/Server "B" fails (i.e., if "A" ceases to receive
advertisements), Proxy/Server "A" can quickly inform Clients by
sending multicast RA messages on the ANET interface.
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Proxy/Server "A" sends RA messages on the ANET interface with source
address set to Proxy/Server "B"'s address, destination address set to
(link-local) All-Nodes multicast, and Router Lifetime set to 0.
Proxy/Server "A" SHOULD send MAX_FINAL_RTR_ADVERTISEMENTS RA messages
separated by small delays [RFC4861]. Any Clients on the ANET that
had been using the failed Proxy/Server "B" will receive the RA
messages and associate with a new Proxy/Server.
3.13.2. Point-to-Multipoint Server Coordination
In environments where Client messaging over ANETs is bandwidth-
limited and/or expensive, Clients can enlist the services of Proxy/
Server "A" to coordinate with multiple Proxy/Servers "B", "C", "D"
etc. 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 Proxy/Servers in MS-Register sub-options of the
OMNI option.
When Proxy/Server "A" receives the RS and processes the OMNI option,
it sends a separate RS to each MS-Register Proxy/Server ID. When
Proxy/Server "A" receives an RA, it can optionally return an
immediate "singleton" RA to the Client or record the Proxy/Server's
ID for inclusion in a pending "aggregate" RA message. Proxy/Server
"A" can then return aggregate RA messages to the Client including
multiple Proxy/Server IDs in order to conserve bandwidth. Each RA
includes a proper subset of the Proxy/Server IDs from the original RS
message, and Proxy/Server "A" must ensure that the message contents
of each RA are consistent with the information received from the
(aggregated) additional Proxy/Servers.
Clients can thereafter employ efficient point-to-multipoint Proxy/
Server coordination under the assistance of Proxy/Server "A" to
reduce the number of messages sent over the ANET while enlisting the
support of multiple Proxy/Servers for fault tolerance. Clients can
further include MS-Release sub-options in IPv6 ND messages to request
Proxy/Server "A" to release from former Proxy/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 RS/RA messaging involved in point-
to-multipoint coordination.
3.14. AERO Address Resolution
While carrier 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:
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o For Clients on VPNed and Direct interfaces, the Proxy/Server is
the ROS.
o For Clients on ANET interfaces, either the Client or the Proxy/
Server may be the ROS.
o For Clients on INET interfaces, the Client itself is the ROS.
o For correspondent nodes on INET/EUN interfaces serviced by a
Relay, the Relay is the ROS.
The route optimization procedure is conducted between the ROS and
with the target Proxy/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 Proxy/Server, or a
non-MNP correspondent reachable via a Relay.
The procedures are specified in the following sections.
3.14.1. Route Optimization Initiation
When an original IP packet from a source node destined to a target
node arrives, the ROS checks for a neighbor cache entry for the LLA
that matches the target destination. If there is a neighbor cache
entry in the REACHABLE state, the ROS invokes the OAL and forwards
the resulting carrier packets according to the cached state and
returns from processing. Otherwise, if there is already a neighbor
cache entry in the STALE state the ROS continues, and if there or no
neighbor cache entry the ROS creates one in the INCOMPLETE state.
The ROS next places the original IP packet on a short queue then
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 minimum/path MPS so that its entire contents will fit
in an OAL first fragment (i.e., as an "atomic fragment"). The ROS
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.
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The NS(AR) message also includes an OMNI option with an Interface
Attributes entry for the sending interface, and with Prefix Length
set to the 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 ULA
corresponding to the target, and with an unpredictable initial
Identification value selected according to [RFC7739]. The source
caches the initial Identification value in the (newly-created)
neighbor cache entry as the starting sequence number for the "send"
window for future carrier packets sent to this target.
The ROS then sends the resulting carrier packet into the spanning
tree without decrementing the network-layer TTL/Hop Limit field.
(When the ROS is an INET Client, it instead must first sign the
NS(AR) message and send the resulting carrier packet to the ADM-ULA
of one of its current Proxy/Servers which then verifies the NS(AR)
signature and forwards the carrier 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 carrier packet containing the RS from
the ROS, it discards the *NET headers and determines the next hop by
consulting its standard IPv6 forwarding table for the OAL header
destination address. The Bridge then decrements the OAL header Hop-
Limit, re-encapsulates the carrier packet and forwards it 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 carrier packet via a secured tunnel to a Proxy/
Server or Relay that services the target.
3.14.3. Processing the NS(AR) and Sending the NA(AR)
When the target Proxy/Server/Relay receives the carrier packet, it
examines the enclosed atomic OAL fragment to determine that it
contains an NS(AR) then examines the NS(AR) target to determine
whether it has a matching neighbor cache entry and/or non-MNP route.
If there is no match, the Proxy/Server/Relay drops the message.
Otherwise, the Proxy/Server continues processing as follows:
o if the NS(AR) target matches a Client neighbor cache entry in the
DEPARTED state, the Proxy/Server inserts an ORH with destination
prefix set to the lower 64 bits of the Client's MNP-ULA and sets
the destination address to the ADM-ULA of the Client's new Proxy/
Server. The (old) Proxy/Server then re-encapsulates the carrier
packet, forwards it into the spanning tree and returns from
processing.
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o If the NS(AR) target matches a Client neighbor cache entry in the
REACHABLE state, the Proxy/Server proceeds according to whether
the Client requires Proxy services. For "dependent" Clients
(e.g., those on low-end ANETs, Direct Links, VPN links, etc.) the
Proxy/Server nominates itself as the ROR; otherwise, the Proxy/
Server re-encapsulates the carrier packet, includes an
authentication signature if necessary, and forwards it to the
target Client which will act as an ROR on its own behalf.
o If the NS(AR) target matches one of its non-MNP routes, the Relay
acts the ROR.
The ROR next checks for a neighbor cache entry that matches the
NS(AR) source LLA. If there is a neighbor cache entry in the
REACHABLE state, the ROR accepts the NS(AR) only if the OAL
Identification value is within the "accept" window for this NS(AR)
source LLA or if the NS(AR) was forwarded securely. If the NS(AR) is
authentic and the OAL Identification is outside of the current
"accept", the ROR resents the current "accept" window start to the
new OAL Identification value while remembering the old value for a
short time in case any carrier packets are still in flight. If there
was no neighbor cache entry in the REACHABLE state, the ROR instead
creates an entry for the NS(AR) source LLA if necessary with state
set to STALE. If the ROR is a Proxy/Server, it next adds a Report
List entry to the target Client neighbor cache entry for the NS(AR)
source LLA while caching the OAL Identification value in the (newly-
created) neighbor cache entry as the starting sequence number for the
"accept" window for future carrier packets received from this LLA
source.
The ROR then prepares a (solicited) NA(AR) message to send back to
the ROS using the same Identification value received in the NS(AR)
(unlike the NS(AR), the NA(AR) need not fit in a single OAL
fragment). The ROR sets the NA(AR) source address to its own LLA,
sets the destination address to the NS(AR) LLA source address and
sets the Target Address to the same value that was in the NS(AR).
The ROR then includes an OMNI option with Prefix Length set to the
length associated with the MNP-LLA.
If the NS(AR) target was an MNP Client, the ROR next includes
Interface Attributes in the OMNI option for each of the target's
underlying interfaces with current information for each interface and
includes an authentication signature if necessary. If the ROR is a
Proxy/Server/Relay, it then sets the S/T-ifIndex field in the OMNI
header set to 0. If the ROR is the Client itself, it instead sets S/
T-ifIndex to the index of the underlying interface that will send the
NS(AR).
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For each Interface Attributes sub-option, the ROR sets the L2ADDR
according to the Proxy/Server's INET address for VPNed or Direct
interfaces, to the INET address of the Proxy/Server for proxyed
interfaces or to the Client's INET address for INET interfaces. The
ROR then includes the lower 32 bits of the Proxy/Server's ADM-ULA 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 Proxy/
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 OAL fragmentation using the same
Identification value that appeared in the NS(AR) and securely
forwards the resulting (*NET-encapsulated) carrier packets without
decrementing the network-layer TTL/Hop Limit field. (When the ROR is
an INET Client, it includes an authentication signature to be
verified by its Proxy/Server; when the ROR is a Proxy/Server, it
forwards the carrier packets over the secured spanning tree to a
Bridge.)
3.14.4. Relaying the NA(AR)
When the Bridge receives the carrier 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 decrements the OAL header Hop-Limit, re-
encapsulates the carrier packet and forwards it 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 carrier packet via a secured tunnel to a Proxy/Server for
the ROS.
3.14.5. Processing the NA(AR)
When the ROS receives the NA(AR) message, it first searches for a
neighbor cache entry that matches the NA(AR) target address. If
there is an entry in the INCOMPLETE or STALE state, the ROS matches
the OAL Identification value with the value it had included in the
corresponding NS(AR). If the values match, the ROS processes the
message the same as for standard IPv6 Address Resolution [RFC4861].
In the process, it caches the target LLA 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
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tree to one of its current Proxy/Servers, which then securely
forwards the message to the Client. If the Client is on an ANET,
ANET physical security and protected spectrum ensures security; if
the Client is on the open ANET, the Proxy/Server must include an
authentication signature.)
3.14.6. Route Optimization Maintenance
Following route optimization, the ROS forwards future carrier packets
with user data destined to the target via the addresses found in the
cached link-layer information and with a monotonically-incrementing
Identification value for each OAL packet. The route optimization is
shared by all sources that send original IP packets to the target via
the ROS, i.e., and not just the source on behalf of which the route
optimization was initiated. Note that route optimization is
performed only for original IP packets that contain user data, and
not for those that contain other IPv6 ND control messages.
While the ROS continues to forward additional original IP packets
destined to the target, 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 may supply a new
unpredictable OAL Identification value if it wishes to reset the
neighbor's "accept" Identification window. If the ROS is an INET
Client, it must sign the NS(AR) message so that the Proxy/Server can
authenticate.
The ROS uses the cached ULA of the ROR (i.e., either the ADM-ULA of
the Proxy/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
original IP 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 carrier 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 carrier packets flowing through the ROS will
again trigger a new route optimization.
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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 and the carrier packet(s) containing the unsolicited NA
include an Identification value within the current "send" window, 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 or the identification value is outside the window, the ROS
simply discards the unsolicited NA.
In this arrangement, the ROS holds a neighbor cache entry with only a
"send" Identification window value for the target, while the ROR
holds a neighbor cache entry with only an "accept" Identification
window value for the ROS. The route optimization neighbor
relationship is therefore asymmetric and unidirectional. If the
target node also has carrier 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.
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 random packets should not be.
AERO nodes can use standard NS/NA(NUD) 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 over the secured
spanning tree, 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 Identification values (and optionally 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
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carrier packets via the spanning tree, maintain a small queue of
carrier packets until target reachability is confirmed, or
(optimistically) allow carrier packets to flow via the route
optimized paths.
When the ROS sends an NS(NUD) message, it sets the IPv6 source to its
own LLA, sets the destination to the LLA of the ROR, and sets the LLA
corresponding to the target 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 an Identification value with the current "send" window (and
optionally Nonce and Timestamp options), then encapsulates the
message in OAL/INET headers with its own ULA as the source and the
ULA of the ROR as the destination. The ROS then forwards the NS(NUD)
message toward the target via a Proxy/Server or Bridge.
When the ROR receives the NS(NUD) message, it creates an NA(NUD) by
reversing the OAL and IPv6 addresses and including an Interface
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
Identification value and Target Address (and optionally the Nonce and
Timestamp) 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.
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3.16. Mobility Management and Quality of Service (QoS)
AERO is a Distributed Mobility Management (DMM) service. Each Proxy/
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 Proxy/Servers via
RS/RA exchanges to maintain the DMM profile, and the AERO routing
system tracks all current Client/Proxy/Server peering relationships.
Proxy/Servers provide default routing and mobility/multilink services
for their dependent Clients. Clients are responsible for maintaining
neighbor relationships with their Proxy/Servers through periodic RS/
RA exchanges, which also serves to confirm neighbor reachability.
When a Client's underlying interface address and/or QoS information
changes, the Client is responsible for updating the Proxy/Server with
this new information. Note that when there is a Proxy/Server in the
path, the Proxy function 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-
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
RORs 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 an ROR sends a uNA message, it sets the
IPv6 source address to the its own LLA, sets the destination address
to (link-local) All-Nodes multicast and sets the Target Address to
the Client's MNP-LLA. The ROR 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 ROR
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 ULA and destination set to the ULA of the ROS and sends the
message into the spanning tree.
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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 Proxy/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 target
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 ROR 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 carrier 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.
In addition to sending uNA messages to the current set of ROSs for
the Client, the ROR 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 ROR sends the
uNA, it sets the IPv6 source address to its LLA, sets the destination
address to the old Proxy/Server's ADM-LLA, and sets the Target
Address to the Client's MNP-LLA. The ROR 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 its
own omIndex if the ROR is a Client or 0 if the ROR is a Proxy/Server.
The ROR 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 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), the Client
requests one of its Proxy/Servers to send RS messages to all of its
other Proxy/Servers via the spanning tree with an OMNI option that
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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 carrier packets containing user data in case one or more RAs
are lost. If all RAs are lost, the Client SHOULD re-associate with a
new Proxy/Server.
When the Proxy/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 Proxy/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 Proxy/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.
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 Proxy/Servers
The Client performs the procedures specified in Section 3.12.2 when
it first associates with a new Proxy/Server or renews its association
with an existing Proxy/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 Proxy/Server to
notify any old Proxy/Servers from which the Client is departing.
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When the new Proxy/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 Proxy/Servers
listed in OMNI option MS-Release identifiers. When the new Proxy/
Server sends a uNA message, 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 LLA.
The new Proxy/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 Proxy/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.
When an old Proxy/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 Proxy/Server's ADM-ULA, and resets
DepartTime. After a short delay (e.g., 2 seconds) the old Proxy/
Server withdraws the Client's MNP from the routing system. After
DepartTime expires, the old Proxy/Server deletes the Client's
neighbor cache entry.
The old Proxy/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 Target address to determine the correct neighbor cache
entry and verifies that the IPv6 destination address matches the old
Proxy/Server. The ROS then caches the IPv6 source address as the new
Proxy/Server for the existing neighbor cache entry and marks the
entry as STALE. While in the STALE state, the ROS allows new carrier
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 Proxy/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 Proxy/Servers in order to
avoid causing excessive oscillations in the AERO routing system.
Examples of when a Client might wish to change to a different Proxy/
Server include a Proxy/Server that has gone unreachable, topological
movements of significant distance, movement to a new geographic
region, movement to a new OMNI link segment, etc.
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When a Client moves to a new Proxy/Server, some of the fragments of a
multiple fragment OAL packet may have already arrived at the old
Proxy/Server while others are en route to the new Proxy/Server,
however no special attention in the reassembly algorithm is necessary
since all fragments will eventually be delivered to the Client which
can then reassemble.
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
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 Proxy/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.
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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/Server Z1 and/or connect via a new Proxy/
Server 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
Proxy/Server Z1 since source S will no longer source any multicast
data traffic via Z1. Instead, the multicast state for (S,G) in
Proxy/Server Z1 will soon time out since no new Joins will arrive.
After some later time, C may move to a new Proxy/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.
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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
original IP 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 original IP 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 original IP 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 original IP packets for group G sourced by S will only
be delivered via the (S, G) tree and not from the (*, G) tree rooted
at R. All mobility considerations discussed for SSM apply.
3.17.3. 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
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would include its own distinct set of Bridges and Proxy/Servers,
thereby providing redundancy in case of failures.
Each OMNI link could utilize the same or different ANET connections.
The links can be distinguished at the link-layer via the SRT prefix
in a similar fashion as for Virtual Local Area Network (VLAN) tagging
(e.g., IEEE 802.1Q) and/or through assignment of distinct sets of
MSPs on each link. This gives rise to the opportunity for supporting
multiple redundant networked paths, 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
original IP 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 original IP packet over multiple hops to the
target.
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 original IPv4 packets to the IPv4 address
mapping of the target MN, and the Relay will translate the IPv4
header and destination address into an IPv6 header and IPv6
destination address of the MN.
When an AERO Client registers with an AERO Proxy/Server, the Proxy/
Server can return the address(es) of DNS servers in RDNSS options
[RFC6106]. The DNS server provides the IP addresses of other MNs and
correspondent nodes in AAAA records for IPv6 or A records for IPv4.
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3.20. Transition/Coexistence Considerations
OAL encapsulation ensures that dissimilar INET partitions can be
joined into a single unified OMNI link, even though the partitions
themselves may have differing protocol versions and/or incompatible
addressing plans. However, a commonality can be achieved by
incrementally distributing globally routable (i.e., native) IP
prefixes to eventually reach all nodes (both mobile and fixed) in all
OMNI link segments. This can be accomplished by incrementally
deploying AERO Bridges on each INET partition, with each Bridge
distributing its MNPs and/or discovering non-MNP IP GUA prefixes on
its INET links.
This gives rise to the opportunity to eventually distribute native IP
addresses to all nodes, and to present a unified OMNI link view even
if the INET partitions remain in their current protocol and
addressing plans. In that way, the OMNI link can serve the dual
purpose of providing a mobility/multilink service and a transition/
coexistence service. Or, if an INET partition is transitioned to a
native IP protocol version and addressing scheme that is compatible
with the OMNI link MNP-based addressing scheme, the partition and
OMNI link can be joined by Bridges.
Relays that connect INETs/EUNs with dissimilar IP protocol versions
may need to employ a network address and protocol translation
function such as NAT64 [RFC6146].
3.21. Detecting and Reacting to Server and Bridge Failures
In environments where rapid failure recovery is required, Proxy/
Servers and Bridges SHOULD use Bidirectional Forwarding Detection
(BFD) [RFC5880]. Nodes that use BFD can quickly detect and react to
failures so that cached information is re-established through
alternate nodes. BFD control messaging is carried only over well-
connected ground domain networks (i.e., and not low-end radio links)
and can therefore be tuned for rapid response.
Proxy/Servers and Bridges maintain BFD sessions in parallel with
their BGP peerings. If a Proxy/Server or Bridge fails, BGP peers
will quickly re-establish routes through alternate paths the same as
for common BGP deployments. Similarly, Proxys maintain BFD sessions
with their associated Bridges even though they do not establish BGP
peerings with them.
Proxys SHOULD use proactive NUD for Proxy/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
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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 Proxy/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
Proxy/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) Proxy/Server will receive the RA messages and
associate with a new Proxy/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 Proxy/
Server in a "tethered" arrangement with all of the Client's traffic
transiting the Proxy/Server. Alternatively, the Client can associate
with an INET Proxy/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
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 an authentication
signature sub-option in the OMNI option
[I-D.templin-6man-omni-interface] to provide message authentication
and submits the RS for OAL encapsulation as an OAL atomic fragment
using an unpredictable Identification value to establish the start of
the "send" window for this Proxy/Server. The Client then
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encapsulates the OAL fragment in UDP/IP headers to form a carrier
packet, sets the UDP/IP source to its INET address and UDP port, sets
the UDP/IP destination to the Proxy/Server's INET address and the
AERO service port number (8060), then sends the carrier packet to the
Proxy/Server.
When the Proxy/Server receives the RS, it discards the OAL
encapsulation, authenticates the RS message, creates a neighbor cache
entry and registers the Client's MNP, Identification and INET
interface information according to the OMNI option parameters. If
the RS message OMNI option includes Interface Attributes with an
L2ADDR, the Proxy/Server compares the encapsulation IP address and
UDP port number with the (unobfuscated) values. If the values are
the same, the Proxy/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
Proxy/Server instead caches the Client's information as "mapped"
addresses meaning that NAT traversal exchanges may be necessary.
The Proxy/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
Proxy/Server also includes an authentication signature sub-option per
[I-D.templin-6man-omni-interface] that contains an acknowledgement of
the update sent by the Client. The Proxy/Server then performs OAL
encapsulation and fragmentation if necessary using the same
Identification value that appeared in the RS, and encapsulates each
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 verifies the OAL
Identification value, performs OAL reassembly if necessary,
authenticates the 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 Proxy/Servers, i.e.,
the same as described in earlier sections.
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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 first creates a neighbor cache
entry for the target in the INCOMPLETE state, then sends the NS(AR)
message to the Proxy/Server with an OMNI option with an
authentication signature sub-option. The Client sets the NS source
address to its own MNP-LLA, destination address to the target
solicited node multicast address and target address to the LLA of the
target. The Client then wraps the NS message in OAL headers (i.e.,
as an atomic OAL fragment) with an unpredictable Identification value
to establish the "send" window for this target, with source address
set to its own MNP-ULA and destination address set to the target's
MNP-ULA. The Client then wraps the atomic OAL fragment in a UDP/IP
header and sends the resulting carrier packet to the Proxy/Server.
When the Client's Proxy/Server receives the OAL-encapsulated NS, it
authenticates the message by processing the authentication signature
sub-option and forwards the message over the spanning tree on behalf
of the Client. When the ROR receives the NS(AR), it creates a
neighbor cache entry for the ROS in the STALE state and caches the
Identification value as the start of the "accept" window for packets
originating from this ROS (if the ROR is a Proxy/Server, it also
creates a Report List entry for this ROS in the target Client's
neighbor cache entry). The ROR then 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 its own LLA, sets the
destination address to the ROS LLA and sets the target address to the
LLA of the target. The ROR then performs OAL encapsulation using the
same Identification value that appeared in the NS(AR), then sets the
OAL source address to the ROR's ULA and destination address to ULA
source of the NS(AR). If the ROR is an INET Client, it includes an
authentication signature and sends the NA(AR) to its Proxy/Sever
which verifies the authentication signature and forwards the NA(AR)
into the secured spanning tree. If the ROR is an ANET Client or a
Proxy/Server, it simply forwards the NA(AR) into the secured spanning
tree.
When the Proxy/Sever for the ROS Client receives the NA(AR) message
contained in one or more carrier packets, it verifies the OAL
Identification matches the same value that was used in the NS(AR)
then reassembles if necessary. When reassembly is complete, the
Proxy/Server includes an authentication signature and forwards the
NA(AR) to the ROS Client. The ROS Client then verifies the
authentication signature and changes the neighbor cache entry state
for this target to REACHABLE.
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Following route optimization for targets in the same OMNI link
segment, if the target's L2ADDR is on the open INET, the Client
forwards carrier 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 carrier packets via its
Proxy/Server until NAT state is populated, then begins forwarding
carrier 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 carrier packets to the Bridge that
returned the NA message.
The ROR may return uNAs via the ROS Proxy/Server if the target moves,
and the Proxy/Server will send corresponding uNAs to the Client with
an OMNI authentication sub-option. 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 can send original IP packets to route-optimized neighbors
in the same OMNI link segment no larger than the minimum/path MPS in
one piece and with OAL encapsulation but without fragmentation. For
larger original 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 original IP packet
or OAL fragment in UDP/IP *NET headers 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 Proxy/Server even if NAT
traversal is not employed.
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
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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
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 Proxy/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,
Templin Expires September 24, 2021 [Page 72]
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control messages exchanged between any pair of OMNI link neighbors on
the spanning tree are already secured.
AERO nodes acting as Route Optimization Responders (RORs) may also
receive 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
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 Proxy/Servers can also provide a network-based VPN
service on behalf of the Client, e.g., if the Client is located
within a secured enclave and cannot establish a VPN on its own
behalf.
AERO Proxy/Servers and Bridges present targets for traffic
amplification Denial of Service (DoS) attacks. This concern is no
different than for widely-deployed VPN security gateways in the
Internet, where attackers could send spoofed packets to the gateways
at high data rates. This can be mitigated by connecting Proxy/
Servers and Bridges over dedicated links with no connections to the
Internet and/or when connections to the Internet are only permitted
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through well-managed firewalls. Traffic amplification DoS attacks
can also target an AERO Client's low data rate links. This is a
concern not only for Clients located on the open Internet but also
for Clients in secured enclaves. AERO Proxy/Servers and Proxys can
institute rate limits that protect Clients from receiving packet
floods that could DoS low data rate links.
AERO Relays must implement ingress filtering to avoid a spoofing
attack in which spurious messages with ULA addresses are injected
into an OMNI link from an outside attacker. AERO Clients MUST ensure
that their connectivity is not used by unauthorized nodes on their
EUNs to gain access to a protected network, i.e., AERO Clients that
act as routers MUST NOT provide routing services for unauthorized
nodes. (This concern is no different than for ordinary hosts that
receive an IP address delegation but then "share" the address with
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.
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
Templin Expires September 24, 2021 [Page 74]
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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]
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.
Templin Expires September 24, 2021 [Page 75]
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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>.
[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>.
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[RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through
Network Address Translations (NATs)", RFC 4380,
DOI 10.17487/RFC4380, February 2006,
<https://www.rfc-editor.org/info/rfc4380>.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
DOI 10.17487/RFC4861, September 2007,
<https://www.rfc-editor.org/info/rfc4861>.
[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862,
DOI 10.17487/RFC4862, September 2007,
<https://www.rfc-editor.org/info/rfc4862>.
[RFC6081] Thaler, D., "Teredo Extensions", RFC 6081,
DOI 10.17487/RFC6081, January 2011,
<https://www.rfc-editor.org/info/rfc6081>.
[RFC7401] Moskowitz, R., Ed., Heer, T., Jokela, P., and T.
Henderson, "Host Identity Protocol Version 2 (HIPv2)",
RFC 7401, DOI 10.17487/RFC7401, April 2015,
<https://www.rfc-editor.org/info/rfc7401>.
[RFC7739] Gont, F., "Security Implications of Predictable Fragment
Identification Values", RFC 7739, DOI 10.17487/RFC7739,
February 2016, <https://www.rfc-editor.org/info/rfc7739>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/info/rfc8200>.
[RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A.,
Richardson, M., Jiang, S., Lemon, T., and T. Winters,
"Dynamic Host Configuration Protocol for IPv6 (DHCPv6)",
RFC 8415, DOI 10.17487/RFC8415, November 2018,
<https://www.rfc-editor.org/info/rfc8415>.
8.2. Informative References
[BGP] Huston, G., "BGP in 2015, http://potaroo.net", January
2016.
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[I-D.bonica-6man-comp-rtg-hdr]
Bonica, R., Kamite, Y., Alston, A., Henriques, D., and L.
Jalil, "The IPv6 Compact Routing Header (CRH)", 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.
[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.
Templin Expires September 24, 2021 [Page 78]
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[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>.
[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>.
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[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>.
[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>.
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[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>.
[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>.
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[RFC5558] Templin, F., Ed., "Virtual Enterprise Traversal (VET)",
RFC 5558, DOI 10.17487/RFC5558, February 2010,
<https://www.rfc-editor.org/info/rfc5558>.
[RFC5569] Despres, R., "IPv6 Rapid Deployment on IPv4
Infrastructures (6rd)", RFC 5569, DOI 10.17487/RFC5569,
January 2010, <https://www.rfc-editor.org/info/rfc5569>.
[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>.
[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>.
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[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>.
[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.
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Appendix A. Non-Normative Considerations
AERO can be applied to a multitude of Internetworking scenarios, with
each having its own adaptations. The following considerations are
provided as non-normative guidance:
A.1. Implementation Strategies for Route Optimization
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.
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
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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, Proxy/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 Proxy/Servers can be standard dedicated server platforms, but
most often will be deployed as virtual machines in the cloud. The
only requirements for Proxy/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, Proxy/Servers must be provisioned,
supported and managed by the INET administrative authority. Cost for
purchasing, configuring and managing Proxy/Servers is nominal
especially for virtual Proxy/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 Proxy/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.
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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 Proxy/Server, and can route between the MNP and non-MNP
address spaces.
A.5. AERO Server Failure Implications
AERO Proxy/Servers may appear as a single point of failure in the
architecture, but such is not the case since all Proxy/Servers on the
link provide identical services and loss of a Proxy/Server does not
imply immediate and/or comprehensive communication failures.
Although Clients typically associate with a single Proxy/Server at a
time, Proxy/Server failure is quickly detected and conveyed by
Bidirectional Forward Detection (BFD) and/or proactive NUD allowing
Clients to migrate to new Proxy/Servers.
If a Proxy/Server fails, ongoing packet forwarding to Clients will
continue by virtue of the neighbor cache entries that have already
been established in route optimization sources (ROSs). If a Client
also experiences mobility events at roughly the same time the Proxy/
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 Proxy/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 Proxy/Server
relationship, after which time continuous communications will resume.
Therefore, providing many Proxy/Servers on the link with high
availability profiles provides resilience against loss of individual
Proxy/Servers and assurance that Clients can establish new Proxy/
Server relationships quickly in event of a Proxy/Server failure.
A.6. AERO Client / Server Architecture
The AERO architectural model is client / server in the control plane,
with route optimization in the data plane. The same as for common
Internet services, the AERO Client discovers the addresses of AERO
Proxy/Servers and selects one Proxy/Server to connect to. The AERO
service is analogous to common Internet services such as google.com,
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yahoo.com, cnn.com, etc. However, there is only one AERO service for
the link and all Proxy/Servers provide identical services.
Common Internet services provide differing strategies for advertising
server addresses to clients. The strategy is conveyed through the
DNS resource records returned in response to name resolution queries.
As of January 2020 Internet-based 'nslookup' services were used to
determine the following:
o When a client resolves the domainname "google.com", the DNS always
returns one A record (i.e., an IPv4 address) and one AAAA record
(i.e., an IPv6 address). The client receives the same addresses
each time it resolves the domainname via the same DNS resolver,
but may receive different addresses when it resolves the
domainname via different DNS resolvers. But, in each case,
exactly one A and one AAAA record are returned.
o When a client resolves the domainname "ietf.org", the DNS always
returns one A record and one AAAA record with the same addresses
regardless of which DNS resolver is used.
o When a client resolves the domainname "yahoo.com", the DNS always
returns a list of 4 A records and 4 AAAA records. Each time the
client resolves the domainname via the same DNS resolver, the same
list of addresses are returned but in randomized order (i.e.,
consistent with a DNS round-robin strategy). But, interestingly,
the same addresses are returned (albeit in randomized order) when
the domainname is resolved via different DNS resolvers.
o When a client resolves the domainname "amazon.com", the DNS always
returns a list of 3 A records and no AAAA records. As with
"yahoo.com", the same three A records are returned from any
worldwide Internet connection point in randomized order.
The above example strategies show differing approaches to Internet
resilience and service distribution offered by major Internet
services. The Google approach exposes only a single IPv4 and a
single IPv6 address to clients. Clients can then select whichever IP
protocol version offers the best response, but will always use the
same IP address according to the current Internet connection point.
This means that the IP address offered by the network must lead to a
highly-available server and/or service distribution point. In other
words, resilience is predicated on high availability within the
network and with no client-initiated failovers expected (i.e., it is
all-or-nothing from the client's perspective). However, Google does
provide for worldwide distributed service distribution by virtue of
the fact that each Internet connection point responds with a
different IPv6 and IPv4 address. The IETF approach is like google
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(all-or-nothing from the client's perspective), but provides only a
single IPv4 or IPv6 address on a worldwide basis. This means that
the addresses must be made highly-available at the network level with
no client failover possibility, and if there is any worldwide service
distribution it would need to be conducted by a network element that
is reached via the IP address acting as a service distribution point.
In contrast to the Google and IETF philosophies, Yahoo and Amazon
both provide clients with a (short) list of IP addresses with Yahoo
providing both IP protocol versions and Amazon as IPv4-only. The
order of the list is randomized with each name service query
response, with the effect of round-robin load balancing for service
distribution. With a short list of addresses, there is still
expectation that the network will implement high availability for
each address but in case any single address fails the client can
switch over to using a different address. The balance then becomes
one of function in the network vs function in the end system.
The same implications observed for common highly-available services
in the Internet apply also to the AERO client/server architecture.
When an AERO Client connects to one or more ANETs, it discovers one
or more AERO Proxy/Server addresses through the mechanisms discussed
in earlier sections. Each Proxy/Server address presumably leads to a
fault-tolerant clustering arrangement such as supported by Linux-HA,
Extended Virtual Synchrony or Paxos. Such an arrangement has
precedence in common Internet service deployments in lightweight
virtual machines without requiring expensive hardware deployment.
Similarly, common Internet service deployments set service IP
addresses on service distribution points that may relay requests to
many different servers.
For AERO, the expectation is that a combination of the Google/IETF
and Yahoo/Amazon philosophies would be employed. The AERO Client
connects to different ANET access points and can receive 1-2 Proxy/
Server ADM-LLAs at each point. It then selects one AERO Proxy/Server
address, and engages in RS/RA exchanges with the same Proxy/Server
from all ANET connections. The Client remains with this Proxy/Server
unless or until the Proxy/Server fails, in which case it can switch
over to an alternate Proxy/Server. The Client can likewise switch
over to a different Proxy/Server at any time if there is some reason
for it to do so. So, the AERO expectation is for a balance of
function in the network and end system, with fault tolerance and
resilience at both levels.
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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.
Author's Address
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Fred L. Templin (editor)
Boeing Research & Technology
P.O. Box 3707
Seattle, WA 98124
USA
Email: fltemplin@acm.org
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