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Network Working Group                                    F. Templin, Ed.
Internet-Draft                                                G. Saccone
Intended status: Informational              Boeing Research & Technology
Expires: December 2, 2018                                       G. Dawra
                                                                LinkedIn
                                                               A. Lindem
                                                     Cisco Systems, Inc.
                                                            May 31, 2018


     A Simple BGP-based Mobile Routing System for the Aeronautical
                       Telecommunications Network
                      draft-templin-atn-bgp-07.txt

Abstract

   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 IPv6-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
   requirements.

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 December 2, 2018.








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Copyright Notice

   Copyright (c) 2018 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
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  ATN/IPS Routing System  . . . . . . . . . . . . . . . . . . .   6
   4.  ATN/IPS Radio Access Network (RAN) Model  . . . . . . . . . .   9
   5.  ATN/IPS Route Optimization  . . . . . . . . . . . . . . . . .  11
   6.  BGP Protocol Considerations . . . . . . . . . . . . . . . . .  13
   7.  Implementation Status . . . . . . . . . . . . . . . . . . . .  14
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  14
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  14
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  15
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  15
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  15
     11.2.  Informative References . . . . . . . . . . . . . . . . .  16
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  17

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 rudimenatary
   short text command and control messages.  The service has seen
   successful deployment in a limited set of worldwide ATM domains.

   The International Civil Aviation Organization [ICAO] is now
   undertaking the development of a next-generation replacement for ATN/
   OSI known as Aeronautical Telecommunications Network with Internet
   Protocol Services (ATN/IPS).  ATN/IPS will eventually provide an
   IPv6-based [RFC8200] service supporting pervasive ATM for Air Traffic
   Controllers (ATC), Airline Operations Controllers (AOC), and all
   commercial aircraft worldwide.  As part of the ATN/IPS undertaking, a



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   new mobile routing service will be needed.  This document presents an
   approach based on the Border Gateway Protocol (BGP) [RFC4271].

   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.

   The ATN/IPS is an IPv6-based overlay network that assumes a worldwide
   connected Internetworking underlay for carrying tunneled ATM
   communications.  The Internetworking underlay could be manifested as
   a private collection of long-haul backbone links (e.g., fiberoptics,
   copper, SATCOM, etc.) interconnected by high-performance networking
   gear such as bridges, switches, and routers.  Such a private network
   would need to connect all ATN/IPS participants worldwide, and could
   therefore present a considerable cost for a large-scale deployment of
   new infrastructure.  Alternatively, the ATN/IPS could be deployed as
   a secured overlay over the existing global public Internet.  For
   example, ATN/IPS nodes could be deployed as part of an SD-WAN or an
   MPLS-WAN that rides over the public Internet via secured tunnels.

   The ATN/IPS further assumes that each aircraft will receive an IPv6
   Mobile Network Prefix (MNP) that accompanies the aircraft wherever it
   travels.  ATCs and AOCs will likewise receive IPv6 prefixes, but they
   would typically appear in static (not mobile) deployments such as air
   traffic control towers, airline headquarters, etc.  Throughout the
   rest of this document, we therefore use the term "MNP" when
   discussing an IPv6 prefix that is delegated to any ATN/IPS end
   system, including ATCs, AOCs, and aircraft.  We also use the term
   Mobility Service Prefix (MSP) to refer to an aggregated 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 /64
   MNPs could be delegated from the MSP 2001:db8::/32).

   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 MNPs in the Internet



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   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 that must be
   propagated to all BGP routers in the Internet that carry a full
   routing table.

   We therefore consider an approach using a BGP overlay network routing
   system where a private BGP routing protocol instance is maintained
   between ATN/IPS Autonomous System (AS) Border Routers (ASBRs).  The
   private BGP instance does not interact with the native BGP routing
   system in the connected Internetworking underlay, 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.

   The s-ASBRs for each stub AS connect to a small number of c-ASBRs via
   dedicated high speed links and/or tunnels across the Internetworking
   underlay using industry-standard encapsulations (e.g., Generic
   Routing Encapsulation (GRE) [RFC2784], IPsec [RFC4301], etc.).  In
   particular, tunneling must be used when neighboringing ASBRs are
   separated by many Internetworking underlay hops.

   The s-ASBRs engage in external BGP (eBGP) peerings with their
   respective c-ASBRs, and only maintain routing table entries for the
   MNPs currently active within the stub AS.  The s-ASBRs send BGP
   updates for 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 using internal BGP (iBGP)
   peerings over which they collaboratively maintain a full routing
   table for all active MNPs currently in service.  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.

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




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2.  Terminology

   The terms Autonomous System (AS) and Autonomous System Border Router
   (ASBR) are the same as defined in [RFC4271].

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

   Air Traffic Managemnet (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.

   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 IPv6-based
      overlay network service that connects access networks via
      tunneling over an Internetworking underlay.

   Internetworking underlay  A connected wide-area network that supports
      overlay network tunneling and connects Radio Access Networks to
      the rest of the ATN/IPS.

   Radio Access Network (RAN)
      An aviation radio data link service provider's network, including
      radio transmitters and receivers as well as suppporting ground-
      domain infrastructure needed to convey a customer's data packets
      to the outside world.  The term RAN is intended in the same spirit
      as for cellular operator networks and other radio-based Internet
      service provider networks.  For simplicity, we also use the term
      RAN to refer to ground-domain networks that connect AOCs and ATCs
      without any aviation radio communications.

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

   Core Autonomous System  The "hub" autonomous system maintained by all
      c-ASBRs.






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

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

   Client  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 network.

   Proxy  A node at the edge of a RAN that acts as an intermediary
      between Clients and s-ASBRs.  From the Client's perspective, the
      Proxy presents the appearance that the Client is communicating
      directly with the s-ASBR.  From the s-ASBR's perspective, the
      Proxy presents the appearance that the s-ASBR is communicating
      directly with the Client.

   Mobile Network Prefix (MNP)  An IPv6 prefix that is delegated to any
      ATN/IPS end system, including ATCs, AOCs, and aircraft.

   Mobility Service Prefix (MSP)  An aggregated 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 /64 MNPs could be
      delegated from the MSP 2001:db8::/32).

3.  ATN/IPS Routing System

   The proposed ATN/IPS routing system comprises a private BGP instance
   coordinated in an overlay network via tunnels between neighboring
   ASBRs over the Internetworking underlay.  The overlay does not
   interact with the native BGP routing system in the connected
   undelying Internetwork, and each c-ASBR advertises only a small and
   unchanging set of MSPs into the Internetworking underlay routing
   system instead of the full dynamically changing set of MNPs.  (For
   example, when the Internetworking underlay is the global public
   Internet the c-ASBRs advertise the MSPs in the public BGP Internet
   routing system.)

   In a reference deployment, one or more s-ASBRs connect each stub AS
   to the overlay using a shared 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 same core AS, and use a shared core ASN.  Since the
   private BGP instance is separate from the global public Internet BGP
   routing system, the ASBRs can use either a private ASN per [RFC6996]
   or simply use public ASNs noting that the ASNs may overlap with those
   already assigned in the Internet.  (A third alternative would be to




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   procure globally-unique public ASNs, but cost and maintenance
   requirements must be conisdered.)

   The c-ASBRs use iBGP to maintain a synchronized consistent view of
   all active MNPs currently in service.  Figure 1 below represents the
   reference 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.

     ...........................................................
   .                                                             .
   .               (:::)-.  <- 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 |              .
   .            +-------+                 +-------+              .
   .                                                             .
   .                                                             .
   .   <------------ Internetworking Underlay  -------------->   .
    ............................................................

                      Figure 1: Reference Deployment





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   In the reference deployment, each s-ASBR maintains routes for active
   MNPs that currently belong to its stub AS.  In response to "Inter-
   domain" mobility events, each s-ASBR will dynamically announces new
   MNPs and withdraws departed 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.

   Each c-ASBR configures a black-hole route for each of its MSPs.  By
   black-holing the MSPs, the c-ASBR will maintain forwarding table
   entries only for the MNPs that are currently active, and packets
   destined to all other MNPs will correctly incur ICMPv6 Destination
   Unreachable messages [RFC4443] due to the black hole route.  (This is
   the same behavior as for ordinary BGP routers in the Internet when
   they receive packets for which there is no route available.)  The
   c-ASBRs do not send eBGP updates for 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 MNPs
   currently within their stub ASes) and they forward all other packets
   to c-ASBRs which have full topology knowledge.

   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 MNPs can be serviced by a
   single set of c-ASBRs and that number could be furhter increased by
   using RRs.  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.  For
   example, if the MSP for the ATN/IPS deployment is 2001:db8::/32, a
   first set of c-ASBRs could service the MSP segment 2001:db8::/40, a
   second set could service 2001:db8:0100::/40, a third set could
   service 2001:db8:0200::/40, etc.

   In this way, each set of c-ASBRs services a specific set of MSPs that
   they inject into the Internetworking underlay native routing system,



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   and each s-ASBR configures MSP-specific routes that list the correct
   set of c-ASBRs as next hops.  This BGP routing design also allows for
   natural incremental deployment, and can support initial small-scale
   deployments followed by dynamic deployment of additional ATN/IPS
   infrastructure elements without disturbing the already-deployed base.

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

   Radio Access Networks (RANs) connect end system Clients such as
   aircraft, ATCs, AOCs etc. to the ATN/IPS routing system.  Clients may
   connect to multiple RANs at once, for example, when they have both
   satellite and cellular data links activated simultaneously.  Clients
   may further move between RANs in a manner that is perceived as a
   network layer mobility event.  Clients could therefore employ a
   multilink/mobility routing service such as that discussed in
   [I-D.templin-aerolink].

   Clients register all of 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 at the edge of the RAN.

   Figure 2 shows the ATN/IPS RAN model where Clients connect to RANs
   via aviation data links.  Clients register their RAN addresses with a
   nearby s-ASBR, where the registration process may be brokered by a
   Proxy at the edge of the RAN.


























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            Data Link "A"     +--------+  Data Link "B"
                 +----------- | Client |-----------+
                /             +--------+            \
               /                                     \
              /                                       \
           (:::)-.                                   (:::)-.
      .-(:::::::::) <- Radio Access Networks -> .-(:::::::::)
        `-(::::)-'                                `-(::::)-'
         +-------+                                +-------+
    ...  | Proxy |  ............................  | Proxy |  ...
   .     +-------+                                +-------+     .
   .         ^^                                      ^^         .
   .         ||                                      ||         .
   .         ||              +--------+              ||         .
   .         ++============> | s-ASBR | <============++         .
   .                         +--------+                         .
   .                              | eBGP                        .
   .                            (:::)-.                         .
   .                        .-(::::::::)                        .
   .                    .-(::: ATN/IPS :::)-.                   .
   .                  (::::: BGP Routing ::::)                  .
   .                     `-(:: System ::::)-'                    .
   .                         `-(:::::::-'                       .
   .                                                            .
   .                                                            .
   .   <------------- Internetworking Underlay ------------->   .
    ............................................................

                    Figure 2: ATN/IPS RAN Architecture

   When a Client logs into a RAN, it specifies a nearby s-ASBR that it
   has selected to connect to the ATN/IPS.  The login process is
   brokered by a Proxy at the border of the RAN, which then conveys the
   connection request to the s-ASBR via tunneling across the
   Internetworking underlay.  The s-ASBR then registers the address of
   the Proxy as the address for the Client, and the Proxy forwards the
   s-ASBR's reply to the Client.  If the Client connects to multiple
   RANs, the s-ASBR will register the addresses of all Proxies as
   addresses through which the Client can be reached.

   The s-ASBR represents all of its active Clients as MNP routes in the
   ATN/IPS BGP routing system.  The s-ASBR's stub AS therefore consists
   of the set of all of its active Clients (i.e., the stub AS is a
   logical construct and not a physical construct).  The s-ASBR injects
   the MNPs of its active Clients and withdraws the MNPs of its departed
   Clients via BGP updates to c-ASBRs.  Since Clients are expected to
   remain associated with their current s-ASBR for extended periods, the
   level of MNP injections and withdrawals in the BGP routing system



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   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
   Proxies and 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 tunnel segments in the forwarding
   path.  In many cases, it would be desirable to eliminate extraneous
   tunnel segments from this "dogleg" route so that packets can traverse
   a minimum number of tunneling hops across the Internetworking
   underlay.  ATN/IPS end systems could therefore employ a route
   optimization service such as that discussed in
   [I-D.templin-aerolink].

   A route optimization example is shown in Figure 3 and Figure 4 below.
   In the first figure, multiple tunneled segments between Proxys and
   ASBRs are necessary to convey packets between Clients associted with
   different s-ASBRs.  In the second figure, the optimized route tunnels
   packets directly between Proxys without involving the ASBRs.
























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         +---------+                             +---------+
         | Client1 |                             | Client2 |
         +---v-----+                             +-----^---+
             *                                         *
             *                                         *
           (:::)-.                                   (:::)-.
      .-(:::::::::) <- Radio Access Networks -> .-(:::::::::)
        `-(::::)-'                                `-(::::)-'
         +--------+                              +--------+
    ...  | Proxy1 |  ..........................  | Proxy2 |  ...
   .     +--------+                              +--------+     .
   .             **                               **            .
   .              **                             **             .
   .               **                           **              .
   .           +---------+                  +---------+         .
   .           | s-ASBR1 |                  | s-ASBR2 |         .
   .           +--+------+                  +-----+---+         .
   .                 \  **      Dogleg      **   /              .
   .              eBGP\  **     Route      **   /eBGP           .
   .                   \  **==============**   /                .
   .                   +---------+   +---------+                .
   .                   | c-ASBR1 |   | c-ASBR2 |                .
   .                   +---+-----+   +----+----+                .
   .                       +--------------+                     .
   .                             iBGP                           .
   .                                                            .
   .   <------------- Internetworking Underlay ------------->   .
    ............................................................

                Figure 3: Dogleg Route Before Optimization





















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         +---------+                             +---------+
         | Client1 |                             | Client2 |
         +---v-----+                             +-----^---+
             *                                         *
             *                                         *
           (:::)-.                                   (:::)-.
      .-(:::::::::)  <- Radio Access Networks -> .-(:::::::::)
        `-(::::)-'                                `-(::::)-'
         +--------+                              +--------+
    ...  | Proxy1 |  ..........................  | Proxy2 |  ...
   .     +------v-+                              +--^-----+     .
   .             *                                  *           .
   .              *================================*            .
   .                                                            .
   .           +---------+                  +---------+         .
   .           | s-ASBR1 |                  | s-ASBR2 |         .
   .           +--+------+                  +-----+---+         .
   .                 \                           /              .
   .              eBGP\                         /eBGP           .
   .                   \                       /                .
   .                   +---------+   +---------+                .
   .                   | c-ASBR1 |   | c-ASBR2 |                .
   .                   +---+-----+   +----+----+                .
   .                       +--------------+                     .
   .                             iBGP                           .
   .                                                            .
   .   <------------- Internetworking Underlay ------------->   .
    ............................................................

                         Figure 4: 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 the system.  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 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 (RRs)[RFC4456].

   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



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   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 bytes (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 and should 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.

   Each c-ASBR will be using eBGP both in the ATN/IPS and the
   Internetworking Underlay with the ATN/IPS unicast IPv6 routes
   resolving over Internetworking Underlay 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 and operational standpoint, the implementation should
   provide isolation between the two BGP routing domains (e.g., separate
   BGP instances).

7.  Implementation Status

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

8.  IANA Considerations

   This document does not introduce any IANA considerations.

9.  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], TLS [RFC5246], etc.




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   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.

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

10.  Acknowledgements

   This work is aligned with the FAA as per the SE2025 contract number
   DTFAWA-15-D-00030.

   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 Information Technology (BIT)
   MobileNet program.

11.  References

11.1.  Normative References

   [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>.

   [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>.

   [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,
              <https://www.rfc-editor.org/info/rfc4456>.







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   [RFC8200]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", STD 86, RFC 8200,
              DOI 10.17487/RFC8200, July 2017,
              <https://www.rfc-editor.org/info/rfc8200>.

11.2.  Informative References

   [BGP]      Huston, G., "BGP in 2015, http://potaroo.net", January
              2016.

   [BGP2]     Huston, G., "BGP Instability Report,
              http://bgpupdates.potaroo.net/instability/bgpupd.html",
              May 2017.

   [CBB]      Dul, A., "Global IP Network Mobility using Border Gateway
              Protocol (BGP), http://www.quark.net/docs/
              Global_IP_Network_Mobility_using_BGP.pdf", March 2006.

   [I-D.templin-aerolink]
              Templin, F., "Asymmetric Extended Route Optimization
              (AERO)", draft-templin-aerolink-82 (work in progress), May
              2018.

   [ICAO]     ICAO, I., "http://www.icao.int/Pages/default.aspx",
              February 2017.

   [RFC2784]  Farinacci, D., Li, T., Hanks, S., Meyer, D., and P.
              Traina, "Generic Routing Encapsulation (GRE)", RFC 2784,
              DOI 10.17487/RFC2784, March 2000,
              <https://www.rfc-editor.org/info/rfc2784>.

   [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>.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246,
              DOI 10.17487/RFC5246, August 2008,
              <https://www.rfc-editor.org/info/rfc5246>.

   [RFC6996]  Mitchell, J., "Autonomous System (AS) Reservation for
              Private Use", BCP 6, RFC 6996, DOI 10.17487/RFC6996, July
              2013, <https://www.rfc-editor.org/info/rfc6996>.








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Authors' Addresses

   Fred L. Templin (editor)
   Boeing Research & Technology
   P.O. Box 3707
   Seattle, WA  98124
   USA

   Email: fltemplin@acm.org


   Greg Saccone
   Boeing Research & Technology
   P.O. Box 3707
   Seattle, WA  98124
   USA

   Email: gregory.t.saccone@boeing.com


   Gaurav Dawra
   LinkedIn
   USA

   Email: gdawra.ietf@gmail.com


   Acee Lindem
   Cisco Systems, Inc.
   USA

   Email: acee@cisco.com



















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