A Simple BGP-based Mobile Routing System for the Aeronautical Telecommunications Network
draft-ietf-rtgwg-atn-bgp-11
Network Working Group F. Templin, Ed.
Internet-Draft G. Saccone
Intended status: Informational Boeing Research & Technology
Expires: January 7, 2022 G. Dawra
LinkedIn
A. Lindem
V. Moreno
Cisco Systems, Inc.
July 6, 2021
A Simple BGP-based Mobile Routing System for the Aeronautical
Telecommunications Network
draft-ietf-rtgwg-atn-bgp-11
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 January 7, 2022.
Templin, et al. Expires January 7, 2022 [Page 1]
Internet-Draft BGP for ATN/IPS July 2021
Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(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 . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. ATN/IPS Routing System . . . . . . . . . . . . . . . . . . . 8
4. ATN/IPS (Radio) Access Network (ANET) Model . . . . . . . . . 12
5. ATN/IPS Route Optimization . . . . . . . . . . . . . . . . . 14
6. BGP Protocol Considerations . . . . . . . . . . . . . . . . . 16
7. Stub AS Mobile Routing Services . . . . . . . . . . . . . . . 18
8. Implementation Status . . . . . . . . . . . . . . . . . . . . 18
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
10. Security Considerations . . . . . . . . . . . . . . . . . . . 18
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 19
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 19
12.1. Normative References . . . . . . . . . . . . . . . . . . 19
12.2. Informative References . . . . . . . . . . . . . . . . . 20
Appendix A. BGP Convergence Considerations . . . . . . . . . . . 21
Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23
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 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][ATN-IPS]. ATN/IPS will eventually
Templin, et al. Expires January 7, 2022 [Page 2]
Internet-Draft BGP for ATN/IPS July 2021
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 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 configured over one or
more Internetworking underlays ("INETs") maintained by aeronautical
network service providers such as ARINC, SITA and Inmarsat. The
overlay provides an Overlay Multilink Network Interface (OMNI)
virtual link layer [I-D.templin-6man-omni] as a Non-Broadcast,
Multiple Access (NBMA) virtual link that spans 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 any two INET partitions use the same IP protocol version nor
have consistent IP addressing plans in comparison with other
partitions. Instead, the OMNI link sees each partition as a
"segment" of a link-layer topology manifested through a (virtual)
bridging service based on IPv6 encapsulation [RFC2473] known as the
OMNI Adaptation Layer (OAL)
[I-D.templin-6man-omni][I-D.templin-6man-aero].
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
Templin, et al. Expires January 7, 2022 [Page 3]
Internet-Draft BGP for ATN/IPS July 2021
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.
The OAL uses ULAs in the source and destination addresses of IPv6
encapsulation headers. Each ULA includes an MNP in the interface
identifier ("MNP-ULA") as discussed in [I-D.templin-6man-omni]. Due
to MNP delegation policies and random MN mobility properties, MNP-
ULAs are generally not aggregatable in the BGP routing service and
are represented as many more-specific prefixes instead of a smaller
number of aggregated prefixes. In addition, OMNI link service nodes
configure administratively-assigned ULAs ("ADM-ULA") that are
statically-assigned and derived from a shorter ADM-ULA prefix
assigned to their OMNI link partition [I-D.templin-6man-omni].
Unlike MNP-ULAs, the ADM-ULAs are persistently present and unchanging
in the routing system. The BGP routing services therefore perform
forwarding based on these MNP-ULAs and ADM-ULAs instead of based on
the GUA MNPs themselves.
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 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
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. BGP routing is based on the ULAs found in OAL headers,
i.e., it provides an adaptation layer forwarding service instead of a
networking layer routing service.
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 INET using
Templin, et al. Expires January 7, 2022 [Page 4]
Internet-Draft BGP for ATN/IPS July 2021
industry-standard secured encapsulations (e.g., IPsec [RFC4301],
Wireguard, etc.). In particular, tunneling must be used when
neighboring ASBRs are separated by multiple INET hops.
The s-ASBRs engage in external BGP (eBGP) peerings with their
respective c-ASBRs, and only maintain routing table entries for the
MNP-ULAs currently active within the stub AS. The s-ASBRs send BGP
updates for MNP-ULA 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 MNP-ULAs currently in service
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 an ADM-ULA
which is taken from an ADM-ULA prefix assigned to each partition, as
well as static forwarding table entries for all other OMNI link
partition prefixes. Both ADM-ULAs and MNP-ULAs are used by the OAL
for nested encapsulation where the inner IPv6 packet is encapsulated
in an IPv6 OAL header with ULA source and destination addresses,
which is then encapsulated in an IP header specific to the INET
partition.
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. The AERO and OMNI services
[I-D.templin-6man-aero][I-D.templin-6man-omni] provide mechanisms for
discovering and utilizing (route-optimized) shortcuts that do not
always follow strict spanning tree paths.
The remainder of this document discusses the proposed BGP-based ATN/
IPS mobile routing service.
Templin, et al. Expires January 7, 2022 [Page 5]
Internet-Draft BGP for ATN/IPS July 2021
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 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.
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 one or more Internetworking underlays.
Internetworking underlay ("INET")
A wide-area network that supports overlay network tunneling 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)
Templin, et al. Expires January 7, 2022 [Page 6]
Internet-Draft BGP for ATN/IPS July 2021
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 GUA-addressed IPv6 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 GUAs. 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 IPv6 layer but above the INET layer that
applies IPv6-in-IPv6 encapsulation prior to INET encapsulation.
The IPv6 encapsulation header inserted by the OAL uses ULAs
instead of GUAs. Further details on OMNI and the OAL are found in
[I-D.templin-6man-omni].
OAL Autonomous System
A "hub-of-hubs" autonomous system maintained through peerings
between the core autonomous systems of different OMNI virtual link
partitions.
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
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
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 or fixed network.
Proxy
An ANET/INET border node that acts as a transparent intermediary
between Clients and s-ASBRs. From the Client's perspective, the
Templin, et al. Expires January 7, 2022 [Page 7]
Internet-Draft BGP for ATN/IPS July 2021
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 /56 MNPs could be delegated from a /24
MSP).
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 overlay does not
interact with the underlying INET BGP routing systems, and only a
small and unchanging set of MSPs are advertised externally instead of
the full dynamically changing set of MNPs.
Within each INET partition, each s-ASBRs 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 assigned need not
be coordinated with IANA and can in fact coincide with values that
are assigned in other domains. The only requirement is that ASNs
must not be duplicated within the ATN/IPS routing system itself.
The c-ASBRs use iBGP to maintain a synchronized consistent view of
all active MNP-ULAs currently in service within the INET partition.
Figure 1 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.
Templin, et al. Expires January 7, 2022 [Page 8]
Internet-Draft BGP for ATN/IPS July 2021
...........................................................
. .
. (:::)-. <- 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 1: INET Partition Reference Deployment
In the reference deployment, each s-ASBR maintains routes for active
MNP-ULAs that currently belong to its stub AS. In response to
"Inter-domain" mobility events, each s-ASBR will dynamically
announces new MNP-ULAs and withdraws departed MNP-ULAs 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
Templin, et al. Expires January 7, 2022 [Page 9]
Internet-Draft BGP for ATN/IPS July 2021
entries only for the MNP-ULAs that are currently active, and packets
destined to all other MNP-ULAs 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 MNP-ULAs 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 MNP-ULAs 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 ADM-ULA that is aggregatable
within an INET partition, and each partition configures a unique ADM-
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 MNP-ULAs 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 ADM-ULA or directly to an end
system by including an MNP-ULA in the destination address of an OAL-
encapsulated packet (see: [I-D.templin-6man-aero]). Figure 2 shows a
reference OAL topology.
Templin, et al. Expires January 7, 2022 [Page 10]
Internet-Draft BGP for ATN/IPS July 2021
. . . . . . . . . . . . . . . . . . . . . . . . .
. .
. .-(::::::::) .
. .-(::::::::::::)-. +------+ .
. (::: Partition 1 ::)--|c-ASBR|---+ .
. `-(::::::::::::)-' +------+ | .
. `-(::::::)-' | .
. | .
. .-(::::::::) | .
. .-(::::::::::::)-. +------+ | .
. (::: Partition 2 ::)--|c-ASBR|---+ .
. `-(::::::::::::)-' +------+ | .
. `-(::::::)-' | .
. | .
. .-(::::::::) | .
. .-(::::::::::::)-. +------+ | .
. (::: Partition 3 ::)--|c-ASBR|---+ .
. `-(::::::::::::)-' +------+ | .
. `-(::::::)-' | .
. | .
. ..(etc).. x .
. .
. .
. <- ATN/IPS Overlay Bridged by the OAL AS -> .
. . . . . . . . . . . . . .. . . . . . . . . . . .
Figure 2: 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 MNP-ULAs 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
Templin, et al. Expires January 7, 2022 [Page 11]
Internet-Draft BGP for ATN/IPS July 2021
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 way, 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 design 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, a few more c-ASBRs could be added 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.
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 both
satellite and cellular data links activated simultaneously. Clients
configure an Overlay Multilink Network (OMNI) Interface
[I-D.templin-6man-omni] over their 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
could therefore employ a multilink/mobility routing service such as
those discussed in Section 7.
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 ANET/INET boundary.
Figure 3 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 at the edge of the ANET.
Templin, et al. Expires January 7, 2022 [Page 12]
Internet-Draft BGP for ATN/IPS July 2021
+-----------------+
| Client |
Data Link "A" +-----------------+ Data Link "B"
+----- | OMNI Interface |--------+
/ +-----------------+ \
/ \
/ \
(:::)-. (:::)-.
.-(:::::::::)<- (Radio) Access Networks ->.-(:::::::::)
`-(::::)-' `-(::::)-'
+-------+ +-------+
... | Proxy | ............................ | Proxy | ...
. +-------+ +-------+ .
. ^^ ^^ .
. || || .
. || +--------+ || .
. ++============> | s-ASBR | <============++ .
. +--------+ .
. | eBGP .
. (:::)-. .
. .-(::::::::) .
. .-(::: ATN/IPS :::)-. .
. (::::: BGP Routing ::::) .
. `-(:: System ::::)-' .
. `-(:::::::-' .
. .
. .
. <------- OMNI virtual link bridged by the OAL --------> .
............................................................
Figure 3: ATN/IPS ANET Architecture
When a Client logs into 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 at the border of the ANET which
then conveys the connection request to the s-ASBR via tunneling
across the OMNI virtual link. Each ANET border Proxy is also equally
capable of serving in the s-ASBR role so that a first on-link Proxy
can be selected as the s-ASBR while all others perform the Proxy role
in a hub-and-spokes arrangement. An on-link Proxy is selected to
serve the s-ASBR role when it receives a control message from a
Client requesting that service.
A network-based s-ASBR can also be selected when the ANET does not
provide a Proxy, or when a different ANET Proxy has already been
selected. Selection of a network-based s-ASBR could be through an
address discovered through a first ANET Proxy, through consulting a
geographically-keyed static host file, through a DNS lookup, through
Templin, et al. Expires January 7, 2022 [Page 13]
Internet-Draft BGP for ATN/IPS July 2021
a network query response, etc. 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
ANETs, 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-ULA 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 MNP-ULAs of its active Clients and withdraws the MNP-ULAs
of its departed Clients via BGP updates to c-ASBRs, which further
propagate the MNP-ULAs 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 MNP-ULA 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 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 spanning tree segments in the
forwarding path. In many cases, it would be desirable to eliminate
extraneous spanning tree segments from this "dogleg" route so that
packets can traverse a minimum number of tunneling 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).
A route optimization example is shown in Figure 4 and Figure 5 below.
In the first figure, multiple spanning tree segments between Proxys
and ASBRs are necessary to convey packets between Clients associated
with different s-ASBRs. In the second figure, the optimized route
tunnels packets directly between Proxys without involving the ASBRs.
Templin, et al. Expires January 7, 2022 [Page 14]
Internet-Draft BGP for ATN/IPS July 2021
+---------+ +---------+
| Client1 | | Client2 |
+---v-----+ +-----^---+
* *
* *
(:::)-. (:::)-.
.-(:::::::::)<- (Radio) Access Networks ->.-(:::::::::)
`-(::::)-' `-(::::)-'
+--------+ +--------+
... | Proxy1 | .......................... | Proxy2 | ...
. +--------+ +--------+ .
. ** ** .
. ** ** .
. ** ** .
. +---------+ +---------+ .
. | s-ASBR1 | | s-ASBR2 | .
. +--+------+ +-----+---+ .
. \ ** Dogleg ** / .
. eBGP\ ** Route ** /eBGP .
. \ **==============** / .
. +---------+ +---------+ .
. | c-ASBR1 | | c-ASBR2 | .
. +---+-----+ +----+----+ .
. +--------------+ .
. iBGP .
. .
. <------- OMNI virtual link bridged by the OAL --------> .
............................................................
Figure 4: Dogleg Route Before Optimization
Templin, et al. Expires January 7, 2022 [Page 15]
Internet-Draft BGP for ATN/IPS July 2021
+---------+ +---------+
| Client1 | | Client2 |
+---v-----+ +-----^---+
* *
* *
(:::)-. (:::)-.
.-(:::::::::) <- (Radio) Access Networks ->.-(:::::::::)
`-(::::)-' `-(::::)-'
+--------+ +--------+
... | Proxy1 | .......................... | Proxy2 | ...
. +------v-+ +--^-----+ .
. * * .
. *================================* .
. .
. +---------+ +---------+ .
. | s-ASBR1 | | s-ASBR2 | .
. +--+------+ +-----+---+ .
. \ / .
. eBGP\ /eBGP .
. \ / .
. +---------+ +---------+ .
. | c-ASBR1 | | c-ASBR2 | .
. +---+-----+ +----+----+ .
. +--------------+ .
. iBGP .
. .
. <------- OMNI virtual link bridged by the OAL --------> .
............................................................
Figure 5: 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 MNP-ULA 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
Templin, et al. Expires January 7, 2022 [Page 16]
Internet-Draft BGP for ATN/IPS July 2021
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 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 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 don't 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
continuity.
Each c-ASBR will be using eBGP both in the ATN/IPS and the INET with
the ATN/IPS unicast IPv6 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 and operational standpoint, the
implementation should provide isolation between the two BGP routing
domains (e.g., separate BGP instances).
ADM-ULAs and MNP-ULAs begin with fd00::/8 followed by a pseudo-random
40-bit global ID to form the prefix [ULA]::/48, along with a 16-bit
OMNI link identifier '*' to form the prefix [ULA*]::/64. Each
individual address taken from [ULA*]::/64 includes additional routing
information in the interface identifier. For example, for the MNP
2001:db8:1:0::/56, the resulting MNP-ULA is [ULA*]:2001:db8:1:0/120,
and for the administrative address 1001:2002/16 the ADM-ULA is
[ULA*]::1001:2002/112 (see: [I-D.templin-6man-omni] for further
details). This gives rise to a BGP routing system that must
accommodate large numbers of long and non-aggregatable MNP-ULA
Templin, et al. Expires January 7, 2022 [Page 17]
Internet-Draft BGP for ATN/IPS July 2021
prefixes as well as moderate numbers of long and semi-aggregatable
ADM-ULA 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.
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] and AERO
[I-D.templin-6man-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 MNP-
ULAs 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], TLS [RFC5246], WireGuard, 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.
Templin, et al. Expires January 7, 2022 [Page 18]
Internet-Draft BGP for ATN/IPS July 2021
This document does not include any new specific requirements for
mitigation of DDoS.
11. 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 Commercial Airplanes (BCA)
Internet of Things (IoT) and autonomy programs.
This work is aligned with the Boeing Information Technology (BIT)
MobileNet program.
The following individuals contributed insights that have improved the
document: Ahmad Amin, Erik Kline, Hubert Kuenig, Tony Li, Alexandre
Petrescu, Pascal Thubert, Tony Whyman.
12. References
12.1. Normative References
[RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in
IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473,
December 1998, <https://www.rfc-editor.org/info/rfc2473>.
[RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005,
<https://www.rfc-editor.org/info/rfc4193>.
[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271,
DOI 10.17487/RFC4271, January 2006,
<https://www.rfc-editor.org/info/rfc4271>.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, DOI 10.17487/RFC4291, February
2006, <https://www.rfc-editor.org/info/rfc4291>.
[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>.
Templin, et al. Expires January 7, 2022 [Page 19]
Internet-Draft BGP for ATN/IPS July 2021
[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>.
[RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,
<https://www.rfc-editor.org/info/rfc5880>.
[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>.
12.2. Informative References
[ATN] Maiolla, V., "The OMNI Interface - An IPv6 Air/Ground
Interface for Civil Aviation, IETF Liaison Statement
#1676, https://datatracker.ietf.org/liaison/1676/", 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)", December 2020.
[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.ietf-lisp-rfc6830bis]
Farinacci, D., Fuller, V., Meyer, D., Lewis, D., and A.
Cabellos, "The Locator/ID Separation Protocol (LISP)",
draft-ietf-lisp-rfc6830bis-36 (work in progress), November
2020.
[I-D.templin-6man-aero]
Templin, F. L., "Automatic Extended Route Optimization
(AERO)", draft-templin-6man-aero-01 (work in progress),
April 2021.
Templin, et al. Expires January 7, 2022 [Page 20]
Internet-Draft BGP for ATN/IPS July 2021
[I-D.templin-6man-omni]
Templin, F. L. and T. Whyman, "Transmission of IP Packets
over Overlay Multilink Network (OMNI) Interfaces", draft-
templin-6man-omni-03 (work in progress), April 2021.
[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>.
[RFC6275] Perkins, C., Ed., Johnson, D., and J. Arkko, "Mobility
Support in IPv6", RFC 6275, DOI 10.17487/RFC6275, July
2011, <https://www.rfc-editor.org/info/rfc6275>.
[RFC6793] Vohra, Q. and E. Chen, "BGP Support for Four-Octet
Autonomous System (AS) Number Space", RFC 6793,
DOI 10.17487/RFC6793, December 2012,
<https://www.rfc-editor.org/info/rfc6793>.
Appendix A. BGP Convergence Considerations
Experimental evidence has shown that BGP convergence time required
for when an MNP-ULA 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 MNP-ULA route that has recently been changed can be
(mis)delivered to an old s-ASBR after a Client has moved to a new
s-ASBR.
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.
Templin, et al. Expires January 7, 2022 [Page 21]
Internet-Draft BGP for ATN/IPS July 2021
Appendix B. Change Log
<< RFC Editor - remove prior to publication >>
Changes from -10 to -11:
o Introduced notion of the spanning tree
o Discussed Proxy/s-ASBR arrangement options.
Changes from -05 to -06:
o OMNI interface introduced
o Version and reference update.
Changes from -04 to -05:
o Version and reference update.
Changes from -03 to -04:
o added discussion of Bidirectional Forwarding Detection (BFD).
Changes from -02 to -03:
o added reference to ICAO A/G interface specification.
Changes from -01 to -02:
o introduced the SPAN and the concept of Internetwork partitioning
o new terms "ANET" (for (Radio) Access Network) and "INET" (for
Internetworking underlay)
o new appendix on BGP convergence considerations
Changes from -00 to -01:
o incorporated clarifications due to list comments and questions.
o new section 7 on Stub AS Mobile Routing Services
o updated references, and included new reference for MIPv6 and LISP
Status as of 08/30/2018:
o 'draft-templin-atn-bgp' becomes 'draft-ietf-rtgwg-atn-bgp'
Templin, et al. Expires January 7, 2022 [Page 22]
Internet-Draft BGP for ATN/IPS July 2021
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
Victor Moreno
Cisco Systems, Inc.
USA
Email: vimoreno@cisco.com
Templin, et al. Expires January 7, 2022 [Page 23]