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A Simple BGP-based Mobile Routing System for the Aeronautical Telecommunications Network

Document Type Active Internet-Draft (rtgwg WG)
Authors Fred Templin , Greg Saccone , Gaurav Dawra , Acee Lindem , Victor Moreno
Last updated 2023-09-19
Replaces draft-templin-atn-bgp
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Stream WG state WG Document
Document shepherd Yingzhen Qu
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Network Working Group                                 F. L. Templin, Ed.
Internet-Draft                                                G. Saccone
Intended status: Informational              Boeing Research & Technology
Expires: 22 March 2024                                          G. Dawra
                                                               A. Lindem
                                                     LabN Consulting LLC
                                                               V. Moreno
                                                     Cisco Systems, Inc.
                                                       19 September 2023

     A Simple BGP-based Mobile Routing System for the Aeronautical
                       Telecommunications Network


   The International Civil Aviation Organization (ICAO) is investigating
   mobile routing solutions for a worldwide Aeronautical
   Telecommunications Network with Internet Protocol Services (ATN/IPS).
   The ATN/IPS will eventually replace existing communication services
   with an IP-based service supporting pervasive Air Traffic Management
   (ATM) for Air Traffic Controllers (ATC), Airline Operations
   Controllers (AOC), and all commercial aircraft worldwide.  This
   informational document describes a simple and extensible mobile
   routing service based on industry-standard BGP to address the ATN/IPS

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   Drafts is at

   Internet-Drafts are draft documents valid for a maximum of six months
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   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 22 March 2024.

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Copyright Notice

   Copyright (c) 2023 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 (
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   7
   3.  ATN/IPS Routing System  . . . . . . . . . . . . . . . . . . .  10
   4.  ATN/IPS (Radio) Access Network (ANET) Model . . . . . . . . .  14
   5.  ATN/IPS Route Optimization  . . . . . . . . . . . . . . . . .  16
   6.  BGP Protocol Considerations . . . . . . . . . . . . . . . . .  19
   7.  Stub AS Mobile Routing Services . . . . . . . . . . . . . . .  21
   8.  Implementation Status . . . . . . . . . . . . . . . . . . . .  21
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  21
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  21
     10.1.  Public Key Infrastructure (PKI) Considerations . . . . .  22
   11. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  22
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  23
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  23
     12.2.  Informative References . . . . . . . . . . . . . . . . .  24
   Appendix A.  BGP Convergence Considerations . . . . . . . . . . .  26
   Appendix B.  AERO/OMNI Spanning Tree Properties . . . . . . . . .  26
   Appendix C.  Change Log . . . . . . . . . . . . . . . . . . . . .  27
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  27

1.  Introduction

   The worldwide Air Traffic Management (ATM) system today uses a
   service known as Aeronautical Telecommunications Network based on
   Open Systems Interconnection (ATN/OSI).  The service is used to
   augment controller to pilot voice communications with rudimentary
   short text command and control messages.  The service has seen
   successful deployment in some worldwide ATM domains.

   The International Civil Aviation Organization (ICAO) is now engaged
   in the development of a next-generation replacement for ATN/OSI known
   as Aeronautical Telecommunications Network with Internet Protocol

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   Services (ATN/IPS) [ATN][ATN-IPS].  ATN/IPS will eventually provide
   an Internetworking service supporting pervasive ATM for Air Traffic
   Controllers (ATC), Airline Operations Controllers (AOC), and all
   commercial aircraft worldwide.  The ATN/IPS will require a new mobile
   routing service as a core element of the architecture.  This document
   presents an approach based on the Border Gateway Protocol (BGP)

   Aircraft communicate via wireless aviation data links that typically
   support much lower data rates than terrestrial wireless and wired-
   line communications.  For example, some Very High Frequency (VHF)-
   based data links only support data rates on the order of 32Kbps and
   an emerging L-Band data link that is expected to play a key role in
   future aeronautical communications only supports rates on the order
   of 1Mbps.  Although satellite data links can provide much higher data
   rates during optimal conditions, like any other aviation data link
   they are subject to errors, delay, disruption, signal intermittence,
   degradation due to atmospheric conditions, etc.  The well-connected
   ground domain ATN/IPS network should therefore treat each safety-of-
   flight critical packet produced by (or destined to) an aircraft as a
   precious commodity and strive for an optimized service that provides
   the highest possible degree of reliability.  Furthermore, continuous
   performance-intensive control messaging services such as BGP peering
   sessions must be carried only over the well-connected ground domain
   ATN/IPS network and never over low-end aviation data links.

   The ATN/IPS is an IP-based overlay network configured over one or
   more Internetworking underlays ("INETs") maintained by aeronautical
   network service providers such as ARINC, SITA and Inmarsat.  The
   Overlay Multilink Network Interface (OMNI) [I-D.templin-intarea-omni]
   uses an adaptation layer encapsulation to create a Non-Broadcast,
   Multiple Access (NBMA) virtual link spanning the entire ATN/IPS.
   Each aircraft connects to the OMNI link via an OMNI interface
   configured over the aircraft's underlying physical and/or virtual
   access network interfaces.

   Each underlying INET comprises one or more "partitions" where all
   nodes within a partition can exchange packets with all other nodes,
   i.e., the partition is connected internally.  There is no requirement
   that each INET partition uses the same IP protocol version nor has
   consistent IP addressing plans in relation to other partitions.
   Instead, the OMNI link sees each partition as a "segment" of a lower
   layer topology concatenated by a service known as the OMNI Adaptation
   Layer (OAL) [I-D.templin-intarea-omni] based on IPv6 encapsulation

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   The IPv6 addressing architecture provides different classes of
   addresses, including Global Unicast Addresses (GUAs), Unique Local
   Addresses (ULAs) and Link-Local Addresses (LLAs) [RFC4291][RFC4193].
   The ATN/IPS receives an IPv6 GUA Mobility Service Prefix (MSP) from
   an Internet assigned numbers authority, and each aircraft will
   receive a Mobile Network Prefix (MNP) delegation from the MSP that
   accompanies the aircraft wherever it travels.  ATCs and AOCs will
   likewise receive MNPs, but they would typically appear in static (not
   mobile) deployments such as air traffic control towers, airline
   headquarters, etc.  (Note that while IPv6 GUAs are assumed for ATN/
   IPS, IPv4 with public/private addresses could also be used.)

   The OAL uses ULAs for adaptation layer addressing.  Each ULA includes
   a prefix beginning with "fd00::/8" followed by a 40-bit Global ID and
   a 16-bit Subnet ID as "fd{Global ID}:{Subnet ID}::/64".  Each
   aircraft ULA includes an MNP in the interface identifier ("ULA-MNP"),
   as discussed in [I-D.templin-intarea-omni].  Due to MNP delegation
   policies and random node mobility properties, ULA-MNPs are generally
   not aggregable in the BGP routing service and are represented as many
   more-specific prefixes instead of a smaller number of aggregated

   BGP routing service infrastructure nodes additionally configure ULAs
   with randomized interface identifiers ("ULA-RND") that are
   statically-assigned and derived from a shorter ULA prefix assigned to
   their BGP network partitions.  Unlike ULA-MNPs, the ULA-RNDs are
   persistently present and unchanging in the routing system.  The BGP
   routing services therefore establish forwarding table entries based
   on these adaptation layer ULA-MNPs and ULA-RNDs instead of based on
   the network layer GUA MNPs.  However, nodes set the 40-bit Global ID
   and 16-bit Subnet ID to 0 ("wildcard") when they advertise ULA-MNPs
   in BGP routing exchanges and/or install ULA-MNPs in forwarding tables
   since the MNP uniquely addresses the aircraft regardless of its
   current BGP network partition affiliation(s).

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   When an OMNI interface forwards an original IP packet, the OAL
   performs IPv6 encapsulation using ULA-RNDs and/or ULA-MNPs as source
   and destination addresses.  The OAL next subjects each resulting "OAL
   packet" to IPv6 fragmentation and header compression, then
   encapsulates each fragment in INET headers specific to the underlying
   Internetwork.  These resulting "carrier packets" then traverse a
   series of Internetworks connected by OAL intermediate nodes which re-
   encapsulate them in new INET headers for traversal of the next
   Internetwork in succession.  (The carrier packets may themselves be
   subject to IP layer fragmentation/reassembly during each successive
   Internetwork traversal at a layer below the OAL.)  The carrier
   packets finally arrive at the OAL destination which performs
   adaptation layer decapsulation and reassembly to restore the original
   IP packet.  A high-level ATN/IPS network diagram is shown in
   Figure 1:

      +------------+     +------------+          +------------+
      | Aircraft 1 |     | Aircraft 2 |   ....   | Aircraft N |
      +------------+     +------------+          +------------+
     (OMNI Interface)   (OMNI Interface)        (OMNI Interface)
            / \                / \                    / \
           /   \    Aviation  /   \      Data Links  /   \
   .                                                             .
   .                            (:::)-.                          .
   .                        .-(::::::::)                         .
   .                    .-(:::: INET 1 ::)-.                     .
   .                   (::::  e.g., IPv6 :::)                    .
   .      ATN/IPS        `-(:::::::::::::)-'     IPv6-based      .
   .                       `-(:::::::-'                          .
   .  OMNI Adaptation                            BGP Mobile      .
   .                            (:::)-.                          .
   .   Layer Overlay        .-(::::::::)       Routing Service   .
   .                    .-(:::: INET 2 ::)-.                     .
   .     (IP GUAs)     (::::  e.g., IPv4 :::)    (IPv6 ULAs)     .
   .                     `-(:::::::::::::)-'                     .
   .                        `-(:::::::-'                         .
   .                                                             .
   .                  (:: additional INETs ::)                   .
   .                                                             .
             |      Fixed       |      Data Links      |
             |                  |                      |
     (OMNI Interface)   (OMNI Interface)        (OMNI Interface)
      +------------+     +------------+          +------------+
      |  ATC/AOC 1 |     |  ATC/AOC 2 |   ....   |  ATC/AOC M |
      +------------+     +------------+          +------------+

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                     Figure 1: ATN/IPS Network Diagram

   Connexion By Boeing [CBB] was an early aviation mobile routing
   service based on dynamic updates in the global public Internet BGP
   routing system.  Practical experience with the approach has shown
   that frequent injections and withdrawals of prefixes in the Internet
   routing system can result in excessive BGP update messaging, slow
   routing table convergence times, and extended outages when no route
   is available.  This is due to both conservative default BGP protocol
   timing parameters (see Section 6) and the complex peering
   interconnections of BGP routers within the global Internet
   infrastructure.  The situation is further exacerbated by frequent
   aircraft mobility events that each result in BGP updates which must
   be propagated to all BGP routers in the Internet with full routing

   We therefore consider a routing system using an overlay network that
   maintains a private BGP routing protocol instance between ATN/IPS
   Autonomous System (AS) Border Routers (ASBRs).  The private BGP
   instance does not interact with the native BGP routing systems in
   underlying INETs, and BGP updates are unidirectional from "stub"
   ASBRs (s-ASBRs) to a small set of "core" ASBRs (c-ASBRs) in a hub-
   and-spokes topology.  No extensions to the BGP protocol are
   necessary, and BGP routing is based on (intermediate-layer) ULAs
   instead of upper- or lower-layer public/private IP prefixes.  This
   allows ASBRs to perform adaptation layer forwarding based on
   intermediate layer IPv6 header information instead of network layer
   forwarding based on upper layer IP header information or link layer
   forwarding based on lower layer IP header information.

   The s-ASBRs for each stub AS connect to a small number of c-ASBRs via
   dedicated high speed links and/or secured tunnels (e.g., IPsec
   [RFC4301], WireGuard [WGD], etc.) over the underlying INET.
   Neighboring ASBRs should use also such IP layer security
   encapsulations over direct physical links to ensure INET layer

   The s-ASBRs engage in external BGP (eBGP) peerings with their
   respective c-ASBRs, and only maintain routing table entries for the
   ULA-MNPs currently active within the stub AS.  The s-ASBRs send BGP
   updates for ULA-MNP injections or withdrawals to c-ASBRs but do not
   receive any BGP updates from c-ASBRs.  Instead, the s-ASBRs maintain
   default routes with their c-ASBRs as the next hop, and therefore hold
   only partial topology information.

   The c-ASBRs connect to other c-ASBRs within the same partition using
   internal BGP (iBGP) peerings over which they collaboratively maintain
   a full routing table for all active ULA-MNPs currently in service

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   within the partition.  Therefore, only the c-ASBRs maintain a full
   BGP routing table and never send any BGP updates to s-ASBRs.  This
   simple routing model therefore greatly reduces the number of BGP
   updates that need to be synchronized among peers, and the number is
   reduced further still when intradomain routing changes within stub
   ASes are processed within the AS instead of being propagated to the
   core.  BGP Route Reflectors (RRs) [RFC4456] can also be used to
   support increased scaling properties.

   When there are multiple INET partitions, the c-ASBRs of each
   partition use eBGP to peer with the c-ASBRs of other partitions so
   that the full set of ULAs for all partitions are known globally among
   all of the c-ASBRs.  Each c/s-ASBR further configures a ULA-RND taken
   from a ULA prefix assigned to each partition, as well as static
   forwarding table entries for all other OMNI link partition prefixes.

   With these intra- and inter-INET BGP peerings in place, a forwarding
   plane spanning tree is established that properly covers the entire
   operating domain.  All nodes in the network can be visited using
   strict spanning tree hops, but in many instances this may result in
   longer paths than are necessary.  AERO [I-D.templin-intarea-aero]
   provides an example service for discovering and utilizing (route-
   optimized) shortcuts that do not always follow strict spanning tree

   The remainder of this document discusses the proposed BGP-based ATN/
   IPS mobile routing service.

2.  Terminology

   The terms Autonomous System (AS) and Autonomous System Border Router
   (ASBR) are the same as defined in [RFC4271].  The term Internet
   Protocol (IP) refers generically to either protocol version unless
   specifically qualified as IPv4 [RFC0791] or IPv6 [RFC8200].

   The following terms are defined for the purposes of this document:

   Air Traffic Management (ATM)
      The worldwide service for coordinating safe aviation operations.

   Air Traffic Controller (ATC)
      A government agent responsible for coordinating with aircraft
      within a defined operational region via voice and/or data Command
      and Control messaging.

   Airline Operations Controller (AOC)
      An airline agent responsible for tracking and coordinating with
      aircraft within their fleet.

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   Aeronautical Telecommunications Network with Internet Protocol
   Services (ATN/IPS)
      A future aviation network for ATCs and AOCs to coordinate with all
      aircraft operating worldwide.  The ATN/IPS will be an IP-based
      overlay network service that connects access networks via
      encapsulation and forwarding over one or more Internetworking

   Internetworking underlay ("INET")
      A wide-area network that supports overlay network encapsulation/
      forwarding and connects Radio Access Networks to the rest of the
      ATN/IPS.  Example INET service providers for civil aviation
      include ARINC, SITA and Inmarsat.

   (Radio) Access Network ("ANET")
      An aviation radio data link service provider's network, including
      radio transmitters and receivers as well as supporting ground-
      domain infrastructure needed to convey a customer's data packets
      to outside INETs.  The term ANET is intended in the same spirit as
      for radio-based Internet service provider networks (e.g., cellular
      operators), but can also refer to ground-domain networks that
      connect AOCs and ATCs.

   partition (or "segment")
      A fully-connected internal subnetwork of an INET in which all
      nodes can communicate with all other nodes within the same
      partition using the same IP protocol version and addressing plan.
      Each INET consists of one or more partitions.

   Overlay Multilink Network Interface (OMNI)
      A virtual layer 2 bridging service that presents an ATN/IPS
      overlay unified link view even though the underlay may consist of
      multiple INET partitions.  The OMNI virtual link is manifested
      through nested encapsulation in which original IP packets from the
      ATN/IPS are first encapsulated in ULA-addressed IPv6 headers which
      are then forwarded to the next hop using INET encapsulation if
      necessary.  Forwarding over the OMNI virtual link is therefore
      based on ULAs instead of the original IP addresses.  In this way,
      packets sent from a source can be conveyed over the OMNI virtual
      link even though there may be many underlying INET partitions in
      the path to the destination.

   OMNI Adaptation Layer (OAL)
      A middle layer below the IP layer but above the INET layer that
      forwards original IP packets by applying IPv6 encapsulation,
      fragmentation and header compression followed by INET
      encapsulation to form "carrier packets".  End systems that
      configure OMNI interfaces act as the OAL source and destination,

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      while intermediate systems with OMNI interfaces act as OAL
      forwarding nodes.  Regardless of the number of intermediate
      systems in the path, the network layer IP TTL/Hop Limit is not
      decremented during (OAL layer) forwarding.  Further details on
      OMNI and the OAL are found in [I-D.templin-intarea-omni].

   OAL Autonomous System (OAL AS)
      A "hub-of-hubs" autonomous system maintained through peerings
      between the core autonomous systems of different OMNI virtual link

   Core Autonomous System Border Router (c-ASBR)
      A BGP router located in the hub of the INET partition hub-and-
      spokes overlay network topology.

   Core Autonomous System (Core AS)
      The "hub" autonomous system maintained by all c-ASBRs within the
      same partition.

   Stub Autonomous System Border Router (s-ASBR)
      A BGP router configured as a spoke in the INET partition hub-and-
      spokes overlay network topology.

   Stub Autonomous System (Stub AS)
      A logical grouping that includes all Clients currently associated
      with a given s-ASBR.

      An ATC, AOC or aircraft that connects to the ATN/IPS as a leaf
      node.  The Client could be a singleton host, or a router that
      connects a mobile or fixed network.

      An ANET/INET border node that acts as a transparent intermediary
      between Clients and s-ASBRs.  From the Client's perspective, the
      Proxy/Server presents the appearance that the Client is
      communicating directly with the s-ASBR.  From the s-ASBR's
      perspective, the Proxy/Server presents the appearance that the
      s-ASBR is communicating directly with the Client.

   Mobile Network Prefix (MNP)
      An IP prefix that is delegated to any ATN/IPS end system,
      including ATCs, AOCs, and aircraft.

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   Mobility Service Prefix (MSP)
      An aggregated IP prefix assigned to the ATN/IPS by an Internet
      assigned numbers authority, and from which all MNPs are delegated
      (e.g., up to 2**32 IPv6 /56 MNPs could be delegated from a /24

3.  ATN/IPS Routing System

   The ATN/IPS routing system comprises a private BGP instance
   coordinated in an overlay network via tunnels between neighboring
   ASBRs over one or more underlying INETs.  The ATN/IPS routing system
   interacts with underlying INET BGP routing systems only through the
   static advertisement of a small and unchanging set of MSPs instead of
   the full dynamically changing set of MNPs.

   Within each INET partition, each s-ASBR connects a stub AS to the
   INET partition core using a distinct stub AS Number (ASN).  Each
   s-ASBR further uses eBGP to peer with one or more c-ASBRs.  All
   c-ASBRs are members of the INET partition core AS, and use a shared
   core ASN.  Unique ASNs are assigned according to the standard 32-bit
   ASN format [RFC4271][RFC6793].  Since the BGP instance does not
   connect with any INET BGP routing systems, the ASNs can be assigned
   from the [RFC6996] 32-bit ASN space which reserves 94,967,295 numbers
   for private use.  The ASNs must be allocated and managed by an ATN/
   IPS assigned numbers authority established by ICAO, which must ensure
   that ASNs are responsibly distributed without duplication and/or

   The c-ASBRs use iBGP to maintain a synchronized consistent view of
   all active ULA-MNPs currently in service within the INET partition.
   Figure 2 below represents the reference INET partition deployment.
   (Note that the figure shows details for only two s-ASBRs (s-ASBR1 and
   s-ASBR2) due to space constraints, but the other s-ASBRs should be
   understood to have similar Stub AS, MNP and eBGP peering
   arrangements.)  The solution described in this document is flexible
   enough to extend to these topologies.

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   .                                                             .
   .               (:::)-.  <- Stub ASes ->  (:::)-.             .
   .   MNPs-> .-(:::::::::)             .-(:::::::::) <-MNPs     .
   .            `-(::::)-'                `-(::::)-'             .
   .             +-------+                +-------+              .
   .             |s-ASBR1+-----+    +-----+s-ASBR2|              .
   .             +--+----+ eBGP \  / eBGP +-----+-+              .
   .                 \           \/            /                 .
   .                  \eBGP      / \          /eBGP              .
   .                   \        /   \        /                   .
   .                    +-------+   +-------+                    .
   .          eBGP+-----+c-ASBR |...|c-ASBR +-----+eBGP          .
   .   +-------+ /      +--+----+   +-----+-+      \ +-------+   .
   .   |s-ASBR +/       iBGP\   (:::)-.  /iBGP      \+s-ASBR |   .
   .   +-------+            .-(::::::::)             +-------+   .
   .       .            .-(::::::::::::::)-.             .       .
   .       .           (::::  Core AS   :::)             .       .
   .   +-------+         `-(:::::::::::::)-'         +-------+   .
   .   |s-ASBR +\      iBGP/`-(:::::::-'\iBGP       /+s-ASBR |   .
   .   +-------+ \      +-+-----+   +----+--+      / +-------+   .
   .          eBGP+-----+c-ASBR |...|c-ASBR +-----+eBGP          .
   .                    +-------+   +-------+                    .
   .                   /                     \                   .
   .                  /eBGP                   \eBGP              .
   .                 /                         \                 .
   .            +---+---+                 +-----+-+              .
   .            |s-ASBR |                 |s-ASBR |              .
   .            +-------+                 +-------+              .
   .                                                             .
   .                                                             .
   .   <----------------- INET Partition  ------------------->   .

               Figure 2: INET Partition Reference Deployment

   In the reference deployment, each s-ASBR maintains routes for active
   ULA-MNPs that currently belong to its stub AS.  In response to
   "Inter-domain" mobility events, each s-ASBR dynamically announces new
   ULA-MNPs and withdraws departed ULA-MNPs in its eBGP updates to
   c-ASBRs.  Since ATN/IPS end systems are expected to remain within the
   same stub AS for extended timeframes, however, intra-domain mobility
   events (such as an aircraft handing off between cell towers) are
   handled within the stub AS instead of being propagated as inter-
   domain eBGP updates.

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   Each c-ASBR configures a black-hole route for each of its MSPs.  By
   black-holing the MSPs, the c-ASBR maintains forwarding table entries
   only for the ULA-MNPs that are currently active.  If an arriving
   packet matches a black-hole route without matching an ULA-MNP, the
   c-ASBR should drop the packet and may also generate an ICMPv6
   Destination Unreachable message [RFC4443], i.e., without forwarding
   the packet outside of the ATN/IPS overlay based on a less-specific

   The c-ASBRs do not send BGP updates for ULA-MNPs to s-ASBRs, but
   instead originate a default route.  In this way, s-ASBRs have only
   partial topology knowledge (i.e., they know only about the active
   ULA-MNPs currently within their stub ASes) and they forward all other
   packets to c-ASBRs which have full topology knowledge.

   Each s-ASBR and c-ASBR configures an ULA-RND that is aggregable
   within an INET partition, and each partition configures a unique ULA
   prefix that is permanently announced into the routing system.  The
   core ASes of each INET partition are joined together through external
   BGP peerings.  The c-ASBRs of each partition establish external
   peerings with the c-ASBRs of other partitions to form a "core-of-
   cores" OMNI link AS.  The OMNI link AS contains the global knowledge
   of all ULA-MNPs deployed worldwide, and supports ATN/IPS overlay
   communications between nodes located in different INET partitions by
   virtue of OAL encapsulation.  OMNI link nodes can then navigate to
   ASBRs by including an ULA-RND or directly to an end system by
   including an ULA-MNP in the destination address of an OAL-
   encapsulated packet (see: [I-D.templin-intarea-aero]).  Figure 3
   shows a reference OAL topology.

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                 . . . . . . . . . . . . . . . . . . . . . . . . .
               .                                                   .
               .              .-(::::::::)                          .
               .           .-(::::::::::::)-.   +------+            .
               .          (::: Partition 1 ::)--|c-ASBR|---+        .
               .           `-(::::::::::::)-'   +------+   |        .
               .              `-(::::::)-'                 |        .
               .                                           |        .
               .              .-(::::::::)                 |        .
               .           .-(::::::::::::)-.   +------+   |        .
               .          (::: Partition 2 ::)--|c-ASBR|---+        .
               .           `-(::::::::::::)-'   +------+   |        .
               .              `-(::::::)-'                 |        .
               .                                           |        .
               .              .-(::::::::)                 |        .
               .           .-(::::::::::::)-.   +------+   |        .
               .          (::: Partition 3 ::)--|c-ASBR|---+        .
               .           `-(::::::::::::)-'   +------+   |        .
               .              `-(::::::)-'                 |        .
               .                                           |        .
               .                ..(etc)..                  x        .
               .                                                    .
               .                                                    .
               .    <- ATN/IPS Overlay Bridged by the OAL AS ->     .
                 . . . . . . . . . . . . . .. . . . . . . . . . . .

                 Figure 3: Spanning Partitions with the OAL

   Scaling properties of this ATN/IPS routing system are limited by the
   number of BGP routes that can be carried by the c-ASBRs.  A 2015
   study showed that BGP routers in the global public Internet at that
   time carried more than 500K routes with linear growth and no signs of
   router resource exhaustion [BGP].  A more recent network emulation
   study also showed that a single c-ASBR can accommodate at least 1M
   dynamically changing BGP routes even on a lightweight virtual
   machine.  Commercially-available high-performance dedicated router
   hardware can support many millions of routes.

   Therefore, assuming each c-ASBR can carry 1M or more routes, this
   means that at least 1M ATN/IPS end system ULA-MNPs can be serviced by
   a single set of c-ASBRs and that number could be further increased by
   using RRs and/or more powerful routers.  Another means of increasing
   scale would be to assign a different set of c-ASBRs for each set of
   MSPs.  In that case, each s-ASBR still peers with one or more c-ASBRs
   from each set of c-ASBRs, but the s-ASBR institutes route filters so
   that it only sends BGP updates to the specific set of c-ASBRs that
   aggregate the MSP.  In this way, each set of c-ASBRs maintains
   separate routing and forwarding tables so that scaling is distributed

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   across multiple c-ASBR sets instead of concentrated in a single
   c-ASBR set.  For example, a first c-ASBR set could aggregate an MSP
   segment A::/32, a second set could aggregate B::/32, a third could
   aggregate C::/32, etc.  The union of all MSP segments would then
   constitute the collective MSP(s) for the entire ATN/IPS, with
   potential for supporting many millions of mobile networks or more.

   In this design, each set of c-ASBRs services a specific set of MSPs,
   and each s-ASBR configures MSP-specific routes that list the correct
   set of c-ASBRs as next hops.  This also allows for natural
   incremental deployment, and can support initial medium-scale
   deployments followed by dynamic deployment of additional ATN/IPS
   infrastructure elements without disturbing the already-deployed base.
   For example, additional c-ASBRs can be added later if the MNP service
   demand ever outgrows the initial deployment.  For larger-scale
   applications (such as unmanned air vehicles and terrestrial vehicles)
   even larger scales can be accommodated by adding more c-ASBRs.

   Consider now that the c-ASBRs provide adaptation layer gateways
   between independent Internetworks to form a true network-of-networks
   supporting the ATN/IPS overlay.  This same arrangement was first
   envisioned by the "Catenet Model for Internetworking"
   [IEN48][IEN48-2] circa 1978.

4.  ATN/IPS (Radio) Access Network (ANET) Model

   (Radio) Access Networks (ANETs) connect end system Clients such as
   aircraft, ATCs, AOCs etc. to the ATN/IPS routing system.  Clients may
   connect to multiple ANETs at once, for example, when they have
   satellite, cellular, WiFi and/or other data links activated
   simultaneously.  Each Client configures an OMNI interface
   [I-D.templin-intarea-omni] over its underlying ANET interfaces as a
   connection to an NBMA virtual link (manifested by the OAL) that spans
   the entire ATN/IPS.  Clients may further move between ANETs in a
   manner that is perceived as a network layer mobility event.  Clients
   should therefore employ a multilink/mobility routing service such as
   those discussed in Section 7.

   Clients register their active data link connections with their
   serving s-ASBRs as discussed in Section 3.  Clients may connect to
   s-ASBRs either directly, or via a Proxy/Server at the ANET/INET

   Figure 4 shows the ATN/IPS ANET model where Clients connect to ANETs
   via aviation data links.  Clients register their ANET addresses with
   a nearby s-ASBR, where the registration process may be brokered by a
   Proxy/Server at the edge of the ANET.

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                        |     Client      |
         Data Link "A"  +-----------------+  Data Link "B"
                 +----- |  OMNI Interface |--------+
                /       +-----------------+         \
               /                                     \
              /                                       \
           (:::)-.                                   (:::)-.
      .-(:::::::::)<- (Radio) Access Networks ->.-(:::::::::)
        `-(::::)-'                                `-(::::)-'
         +-------+                                +-------+
    ...  |  P/S  |  ............................  |  P/S  |  ...
   .     +-------+                                +-------+     .
   .         ^^                                      ^^         .
   .         ||                                      ||         .
   .         ||              +--------+              ||         .
   .         ++============> | s-ASBR | <============++         .
   .                         +--------+                         .
   .                              | eBGP                        .
   .                            (:::)-.                         .
   .                        .-(::::::::)                        .
   .                    .-(::: ATN/IPS :::)-.                   .
   .                  (::::: BGP Routing ::::)                  .
   .                     `-(:: System ::::)-'                   .
   .                         `-(:::::::-'                       .
   .                                                            .
   .                                                            .
   .  <------- OMNI virtual link bridged by the OAL -------->   .

                    Figure 4: ATN/IPS ANET Architecture

   When a Client connects to an ANET it specifies a nearby s-ASBR that
   it has selected to connect to the ATN/IPS.  The login process is
   transparently brokered by a Proxy/Server at the border of the ANET
   which then conveys the connection request to the s-ASBR via
   adaptation layer encapsulation and forwarding across the OMNI virtual
   link.  Each ANET border Proxy/Server is also equally capable of
   serving in the s-ASBR role so that a first on-link Proxy/Server can
   be selected as the s-ASBR while all others perform the Proxy/Server
   role in a hub-and-spokes arrangement.  An on-link Proxy/Server is
   selected to serve the s-ASBR role when it receives a control message
   from a Client requesting that service.

   The Client can coordinate with a network-based s-ASBR over additional
   ANETs after it has already coordinated with a first-hop Proxy/Server
   over a first ANET.  If the Client connects to multiple ANETs, the
   s-ASBR will register the individual ANET Proxy/Servers as conduits

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   through which the Client can be reached.  The Client then sees the
   s-ASBR as the "hub" in a "hub-and-spokes" arrangement with the first-
   hop Proxy/Servers as spokes.  Selection of a network-based s-ASBR is
   through the discovery methods specified in relevant mobility and
   virtual link coordination specifications (e.g., see AERO
   [I-D.templin-intarea-aero] and OMNI [I-D.templin-intarea-omni]).

   The s-ASBR represents all of its active Clients as ULA-MNP routes in
   the ATN/IPS BGP routing system.  The s-ASBR's stub AS is therefore
   used only to advertise the set of MNPs of all its active Clients to
   its BGP peer c-ASBRs and not to peer with other s-ASBRs (i.e., the
   stub AS is a logical construct and not a physical one).  The s-ASBR
   injects the ULA-MNPs of its active Clients and withdraws the ULA-MNPs
   of its departed Clients via BGP updates to c-ASBRs, which further
   propagate the ULA-MNPs to other c-ASBRs within the OAL AS.  Since
   Clients are expected to remain associated with their current s-ASBR
   for extended periods, the level of ULA-MNP injections and withdrawals
   in the BGP routing system will be on the order of the numbers of
   network joins, leaves and s-ASBR handovers for aircraft operations
   (see: Section 6).  It is important to observe that fine-grained
   events such as Client mobility and Quality of Service (QoS) signaling
   are coordinated only by the Client's current s-ASBRs, and do not
   involve other ASBRs in the routing system.  In this way, intradomain
   routing changes within the stub AS are not propagated into the rest
   of the ATN/IPS BGP routing system.

5.  ATN/IPS Route Optimization

   ATN/IPS end systems will frequently need to communicate with
   correspondents associated with other s-ASBRs.  In the BGP peering
   topology discussed in Section 3, this can initially only be
   accommodated by including multiple extraneous hops and/or spanning
   tree segments in the forwarding path.  In many cases, it would be
   desirable to establish a "short cut" around this "dogleg" route so
   that packets can traverse a minimum number of forwarding hops across
   the OMNI virtual link.  ATN/IPS end systems could therefore employ a
   route optimization service according to the mobility service employed
   (see: Section 7).

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   Each s-ASBR provides designated routing services for only a subset of
   all active Clients, and instead acts as a simple Proxy/Server for
   other Clients.  As a designated router, the s-ASBR advertises the
   MNPs of each of its active Clients into the ATN/IPS routing system
   and provides basic (unoptimized) forwarding services when necessary.
   An s-ASBR could be the first-hop ATN/IPS service access point for
   some, all or none of a Client's underlying interfaces, while the
   Client's other underlying interfaces employ the Proxy/Server function
   of other s-ASBRs.  Route optimization allows Client-to-Client
   communications while bypassing s-ASBR designated routing services
   whenever possible.

   A route optimization example is shown in Figure 5 and Figure 6 below.
   In the first figure, multiple spanning tree segments between Proxy/
   Servers and ASBRs are necessary to convey packets between Clients
   associated with different s-ASBRs.  In the second figure, the
   optimized route forwards encapsulated packets directly between Proxy/
   Servers without involving the ASBRs.

   These route optimized paths are established through secured control
   plane messaging (i.e., over secured tunnels and/or using higher-layer
   control message authentications) but do not provide lower-layer
   security for the data plane.  Data communications over these route
   optimized paths should therefore employ higher-layer security.

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         +---------+                             +---------+
         | Client1 |                             | Client2 |
         +---v-----+                             +-----^---+
             *                                         *
             *                                         *
           (:::)-.                                   (:::)-.
      .-(:::::::::)<- (Radio) Access Networks ->.-(:::::::::)
        `-(::::)-'                                `-(::::)-'
         +--------+                              +--------+
    ...  | P/S-1  |  ..........................  | P/S-2  |  ...
   .     +--------+                              +--------+     .
   .             **                               **            .
   .              **                             **             .
   .               **                           **              .
   .           +---------+                  +---------+         .
   .           | s-ASBR1 |                  | s-ASBR2 |         .
   .           +--+------+                  +-----+---+         .
   .                 \  **      Dogleg      **   /              .
   .              eBGP\  **     Route      **   /eBGP           .
   .                   \  **==============**   /                .
   .                   +---------+   +---------+                .
   .                   | c-ASBR1 |   | c-ASBR2 |                .
   .                   +---+-----+   +----+----+                .
   .                       +--------------+                     .
   .                             iBGP                           .
   .                                                            .
   .  <------- OMNI virtual link bridged by the OAL -------->   .

                 Figure 5: Dogleg Route Before Optimization

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         +---------+                             +---------+
         | Client1 |                             | Client2 |
         +---v-----+                             +-----^---+
             *                                         *
             *                                         *
           (:::)-.                                   (:::)-.
      .-(:::::::::) <- (Radio) Access Networks ->.-(:::::::::)
        `-(::::)-'                                `-(::::)-'
         +--------+                              +--------+
    ...  | P/S-1  |  ..........................  | P/S-2  |  ...
   .     +------v-+                              +--^-----+     .
   .             *                                  *           .
   .              *================================*            .
   .                                                            .
   .           +---------+                  +---------+         .
   .           | s-ASBR1 |                  | s-ASBR2 |         .
   .           +--+------+                  +-----+---+         .
   .                 \                           /              .
   .              eBGP\                         /eBGP           .
   .                   \                       /                .
   .                   +---------+   +---------+                .
   .                   | c-ASBR1 |   | c-ASBR2 |                .
   .                   +---+-----+   +----+----+                .
   .                       +--------------+                     .
   .                             iBGP                           .
   .                                                            .
   .  <------- OMNI virtual link bridged by the OAL -------->   .

                         Figure 6: Optimized Route

6.  BGP Protocol Considerations

   The number of eBGP peering sessions that each c-ASBR must service is
   proportional to the number of s-ASBRs in its local partition.
   Network emulations with lightweight virtual machines have shown that
   a single c-ASBR can service at least 100 eBGP peerings from s-ASBRs
   that each advertise 10K ULA-MNP routes (i.e., 1M total).  It is
   expected that robust c-ASBRs can service many more peerings than this
   - possibly by multiple orders of magnitude.  But even assuming a
   conservative limit, the number of s-ASBRs could be increased by also
   increasing the number of c-ASBRs.  Since c-ASBRs also peer with each
   other using iBGP, however, larger-scale c-ASBR deployments may need
   to employ an adjunct facility such as BGP Route Reflectors

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   The number of aircraft in operation at a given time worldwide is
   likely to be significantly less than 1M, but we will assume this
   number for a worst-case analysis.  Assuming a worst-case average 1
   hour flight profile from gate-to-gate with 10 service region
   transitions per flight, the entire system will need to service at
   most 10M BGP updates per hour (2778 updates per second).  This number
   is within the realm of the peak BGP update messaging seen in the
   global public Internet today [BGP2].  Assuming a BGP update message
   size of 100 octets (800bits), the total amount of BGP control message
   traffic to a single c-ASBR will be less than 2.5Mbps which is a
   nominal rate for modern data links.

   Industry standard BGP routers provide configurable parameters with
   conservative default values.  For example, the default hold time is
   90 seconds, the default keepalive time is 1/3 of the hold time, and
   the default MinRouteAdvertisementinterval is 30 seconds for eBGP
   peers and 5 seconds for iBGP peers (see Section 10 of [RFC4271]).
   For the simple mobile routing system described herein, these
   parameters can be set to more aggressive values to support faster
   neighbor/link failure detection and faster routing protocol
   convergence times.  For example, a hold time of 3 seconds and a
   MinRouteAdvertisementinterval of 0 seconds for both iBGP and eBGP.

   Instead of adjusting BGP default time values, BGP routers can use the
   Bidirectional Forwarding Detection (BFD) protocol [RFC5880] to
   quickly detect link failures that do not result in interface state
   changes, BGP peer failures, and administrative state changes.  BFD is
   important in environments where rapid response to failures is
   required for routing reconvergence and, hence, communications

   Each c-ASBR will be using eBGP both in the ATN/IPS and the INET with
   the ATN/IPS unicast IP routes resolving over INET routes.
   Consequently, c-ASBRs and potentially s-ASBRs will need to support
   separate local ASes for the two BGP routing domains and routing
   policy or assure routes are not propagated between the two BGP
   routing domains.  From a conceptual, operational and correctness
   standpoint, the implementation should provide isolation between the
   two BGP routing domains (e.g., separate BGP instances).

   This gives rise to a BGP routing system that must accommodate large
   numbers of long and non-aggregable ULA-MNP prefixes as well as
   moderate numbers of long and semi-aggregable ULA-RND prefixes.  The
   system is kept stable and scalable through the s-ASBR / c-ASBR hub-
   and-spokes topology which ensures that mobility-related churn is not
   exposed to the core.

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7.  Stub AS Mobile Routing Services

   Stub ASes maintain intradomain routing information for mobile node
   clients, and are responsible for all localized mobility signaling
   without disturbing the BGP routing system.  Clients can enlist the
   services of a candidate mobility service such as Mobile IPv6 (MIPv6)
   [RFC6275], LISP [I-D.ietf-lisp-rfc6830bis] or AERO
   [I-D.templin-intarea-aero] according to the service offered by the
   stub AS.  Further details of mobile routing services are out of scope
   for this document.

8.  Implementation Status

   The BGP routing topology described in this document has been modeled
   in realistic network emulations showing that at least 1 million ULA-
   MNPs can be propagated to each c-ASBR even on lightweight virtual
   machines.  No BGP routing protocol extensions need to be adopted.

9.  IANA Considerations

   This document does not introduce any IANA considerations.

10.  Security Considerations

   ATN/IPS ASBRs on the open Internet are susceptible to the same attack
   profiles as for any Internet nodes.  For this reason, ASBRs should
   employ physical security and/or IP securing mechanisms such as IPsec
   [RFC4301], WireGuard [WGD], etc.

   ATN/IPS ASBRs present targets for Distributed Denial of Service
   (DDoS) attacks.  This concern is no different than for any node on
   the open Internet, where attackers could send spoofed packets to the
   node at high data rates.  This can be mitigated by connecting ATN/IPS
   ASBRs over dedicated links with no connections to the Internet and/or
   when ASBR connections to the Internet are only permitted through
   well-managed firewalls.

   ATN/IPS s-ASBRs should institute rate limits to protect low data rate
   aviation data links from receiving DDoS packet floods.

   BGP protocol message exchanges and control message exchanges used for
   route optimization must be secured to ensure the integrity of the
   system-wide routing information base.  Security is based on IP layer
   security associations between peers which ensure confidentiality,
   integrity and authentication over secured tunnels (see above).
   Higher layer security protection such as TCP-AO [RFC5926] is
   therefore optional, since it would be redundant with the security
   provided at lower layers.

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   Data communications over route optimized paths should employ end-to-
   end higher-layer security since only the control plane and
   unoptimized paths are protected by lower-layer security.  End-to-end
   higher-layer security mechanisms include QUIC-TLS [RFC9001], TLS
   [RFC8446], DTLS [RFC6347], SSH [RFC4251], etc. applied in a manner
   outside the scope of this document.

   This document does not include any new specific requirements for
   mitigation of DDoS.

10.1.  Public Key Infrastructure (PKI) Considerations

   In development of the overall ATN/IPS operational concept, ICAO
   addressed the security concerns in multiple ways to ensure
   coordination and consistency across the various groups.  This also
   avoided potential duplicative work.  Technical provisions related
   specifically to the operation of ATN/IPS are specified in supporting
   ATN/IPS standards.  However, other considerations such as the
   establishment of a PKI, were determined to have an impact beyond ATN/
   IPS.  ICAO created a Trust Framework Study Group (TFSG) to define
   various governance, policy, procedures and overall technical
   performance requirements for system connectivity and

   As part of their charter, the TSFG is specifically developing a
   concept of operations for a common aviation digital trust framework
   and principles to facilitate an interoperable secure, cyber resilient
   and seamless exchange of information in a digitally connected
   environment.  They are also developing governance principles, policy,
   procedures and requirements for establishing digital identity for a
   global trust framework that will consider any exchange of information
   among users of the aviation ecosystem, and to promote these concepts
   with all relevant stakeholders.

   ATN/IPS will take advantage of the developments of TFSG within the
   overall ATN/IPS operational concept.  As such, this will include the
   usage of the PKI specification resulting from the TFSG.

11.  Acknowledgements

   This work is aligned with the FAA as per the SE2025 contract number

   This work is aligned with the NASA Safe Autonomous Systems Operation
   (SASO) program under NASA contract number NNA16BD84C.

   This work is aligned with the Boeing Commercial Airplanes (BCA)
   Internet of Things (IoT) and autonomy programs.

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   This work is aligned with the Boeing Information Technology (BIT)
   MobileNet program.

   The following individuals contributed insights that have improved the
   document: Ahmad Amin, Mach Chen, Russ Housley, Erik Kline, Hubert
   Kuenig, Tony Li, Gyan Mishra, Alexandre Petrescu, Dave Thaler, Pascal
   Thubert, Michael Tuxen, Eric Vyncke, Tony Whyman.  Vaughn Maiolla is
   further remembered for his support and guidance.

   Honoring life, liberty and the pursuit of happiness.

12.  References

12.1.  Normative References

   [RFC0791]  Postel, J., "Internet Protocol", STD 5, RFC 791,
              DOI 10.17487/RFC0791, September 1981,

   [RFC2473]  Conta, A. and S. Deering, "Generic Packet Tunneling in
              IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473,
              December 1998, <>.

   [RFC4193]  Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
              Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005,

   [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,

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, DOI 10.17487/RFC4291, February
              2006, <>.

   [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,

   [RFC4456]  Bates, T., Chen, E., and R. Chandra, "BGP Route
              Reflection: An Alternative to Full Mesh Internal BGP
              (IBGP)", RFC 4456, DOI 10.17487/RFC4456, April 2006,

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   [RFC5880]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,

   [RFC8200]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", STD 86, RFC 8200,
              DOI 10.17487/RFC8200, July 2017,

12.2.  Informative References

   [ATN]      Maiolla, V., "The OMNI Interface - An IPv6 Air/Ground
              Interface for Civil Aviation, IETF Liaison Statement
              #1676,", 3
              March 2020.

   [ATN-IPS]  WG-I, ICAO., "ICAO Document 9896 (Manual on the
              Aeronautical Telecommunication Network (ATN) using
              Internet Protocol Suite (IPS) Standards and Protocol),
              Draft Edition 3 (work-in-progress)", 10 December 2020.

   [BGP]      Huston, G., "BGP in 2015,", January

   [BGP2]     Huston, G., "BGP Instability Report,
              May 2017.

   [CBB]      Dul, A., "Global IP Network Mobility using Border Gateway
              Protocol (BGP),
              Global_IP_Network_Mobility_using_BGP.pdf", March 2006.

              Farinacci, D., Fuller, V., Meyer, D., Lewis, D., and A.
              Cabellos-Aparicio, "The Locator/ID Separation Protocol
              (LISP)", Work in Progress, Internet-Draft, draft-ietf-
              lisp-rfc6830bis-38, 7 May 2022,

              Templin, F., "Automatic Extended Route Optimization
              (AERO)", Work in Progress, Internet-Draft, draft-templin-
              intarea-aero-34, 11 September 2023,

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              Templin, F., "Transmission of IP Packets over Overlay
              Multilink Network (OMNI) Interfaces", Work in Progress,
              Internet-Draft, draft-templin-intarea-omni-34, 11
              September 2023, <

   [IEN48]    Cerf, V., "The Catenet Model For Internetworking,
    ", July 1978.

   [IEN48-2]  Cerf, V., "The Catenet Model For Internetworking (with
              figures),", July

   [RFC4251]  Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)
              Protocol Architecture", RFC 4251, DOI 10.17487/RFC4251,
              January 2006, <>.

   [RFC4301]  Kent, S. and K. Seo, "Security Architecture for the
              Internet Protocol", RFC 4301, DOI 10.17487/RFC4301,
              December 2005, <>.

   [RFC5926]  Lebovitz, G. and E. Rescorla, "Cryptographic Algorithms
              for the TCP Authentication Option (TCP-AO)", RFC 5926,
              DOI 10.17487/RFC5926, June 2010,

   [RFC6275]  Perkins, C., Ed., Johnson, D., and J. Arkko, "Mobility
              Support in IPv6", RFC 6275, DOI 10.17487/RFC6275, July
              2011, <>.

   [RFC6347]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
              Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
              January 2012, <>.

   [RFC6793]  Vohra, Q. and E. Chen, "BGP Support for Four-Octet
              Autonomous System (AS) Number Space", RFC 6793,
              DOI 10.17487/RFC6793, December 2012,

   [RFC6996]  Mitchell, J., "Autonomous System (AS) Reservation for
              Private Use", BCP 6, RFC 6996, DOI 10.17487/RFC6996, July
              2013, <>.

   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,

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   [RFC9001]  Thomson, M., Ed. and S. Turner, Ed., "Using TLS to Secure
              QUIC", RFC 9001, DOI 10.17487/RFC9001, May 2021,

   [WGD]      Donenfeld, J., "WireGuard: Fast, Modern, Secure VPN
              Tunnel,", February 2022.

Appendix A.  BGP Convergence Considerations

   Experimental evidence has shown that BGP convergence time required
   after an ULA-MNP is asserted at a new location or withdrawn from an
   old location can be several hundred milliseconds even under optimal
   AS peering arrangements.  This means that packets in flight destined
   to an ULA-MNP route that has recently been changed can be
   (mis)delivered to an old s-ASBR after a Client has moved to a new

   To address this issue, the old s-ASBR can maintain temporary state
   for a "departed" Client that includes an OAL address for the new
   s-ASBR.  The OAL address never changes since ASBRs are fixed
   infrastructure elements that never move.  Hence, packets arriving at
   the old s-ASBR can be forwarded to the new s-ASBR while the BGP
   routing system is still undergoing reconvergence.  Therefore, as long
   as the Client associates with the new s-ASBR before it departs from
   the old s-ASBR (while informing the old s-ASBR of its new location)
   packets in flight during the BGP reconvergence window are
   accommodated without loss.

Appendix B.  AERO/OMNI Spanning Tree Properties

   The AERO/OMNI services establish an adaptation layer for the OSI
   reference model appearing as "the layer below the network layer but
   above the data link layer".  The adaptation layer presents a virtual
   bridging service from the network layer's perspective and a BGP-based
   IPv6 routing service from the data link layer's perspective.

   AERO/OMNI overlay networks include s-ASBRs (aka Proxy/Servers) and
   c-ASBRs (aka Gateways) as the vertices in a graph with a typically
   sparse collection of edges between pairwise vertices.  The graph
   minimally comprises a true spanning tree connecting all vertices but
   may also include additional edges in the spirit of IEEE 802.1aq
   Shortest Path Bridging.  BGP routing then ensures loop freedom even
   if this "augmented" spanning tree includes cycles.

   Each edge in the spanning tree corresponds to one or more connecting
   links which may be physical (e.g., fiber/free-space optics, etc.) or
   virtual (an IP tunnel over an underlying Internetwork).  The OMNI
   interface provides a nexus for link selection, where control messages

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   between vertices must be forwarded over edge links that are secured
   at the network layer or below while data messages may be forwarded
   over unsecured links.  AERO/OMNI refer to these distinct forwarding
   contexts as the "secured spanning tree" and "unsecured spanning
   tree", respectively.

   AERO route optimization provides an essential service to establish
   shortcut paths in the data plane that do not necessarily follow
   strict spanning tree paths.  The shortcuts are formed through secured
   spanning tree control message exchanges which establish shortest path
   forwarding state in Clients, Proxy/Servers and intermediate Gateways.
   Route optimization therefore reduces spanning tree traffic
   concentration and instead distributes traffic over a diversity of
   underlying Internetwork paths.

Appendix C.  Change Log

   << RFC Editor - remove prior to publication >>

   Differences from earlier versions:

   *  Submit for Rtgwg Informational Track RFC publication.

Authors' Addresses

   Fred L. Templin (editor)
   Boeing Research & Technology
   P.O. Box 3707
   Seattle, WA 98124
   United States of America

   Greg Saccone
   Boeing Research & Technology
   P.O. Box 3707
   Seattle, WA 98124
   United States of America

   Gaurav Dawra
   United States of America

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   Acee Lindem
   LabN Consulting LLC
   United States of America

   Victor Moreno
   Cisco Systems, Inc.
   United States of America

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