Scalable De-Aggregation for Overlays Using the Border Gateway Protocol (BGP)
draft-templin-rtgwg-scalable-bgp-00
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| Document | Type | Active Internet-Draft (individual) | |
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| Author | Fred Templin | ||
| Last updated | 2019-01-23 | ||
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draft-templin-rtgwg-scalable-bgp-00
Network Working Group F. Templin, Ed.
Internet-Draft Boeing Research & Technology
Intended status: Informational January 23, 2019
Expires: July 27, 2019
Scalable De-Aggregation for Overlays Using the Border Gateway Protocol
(BGP)
draft-templin-rtgwg-scalable-bgp-00.txt
Abstract
The Border Gateway Protocol (BGP) has well-known limitations in terms
of the numbers of routes that can be carried and stability of the
routing system. This is especially true when mobile nodes frequently
change their network attachment points, which in the past has
resulted in excessive announcements and withdrawals of de-aggregated
prefixes. This document discusses a means of accommodating scalable
de-aggregation of IPv6 prefixes for overlay networks using BGP.
Status of This Memo
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This Internet-Draft will expire on July 27, 2019.
Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the
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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. Overview and Analysis . . . . . . . . . . . . . . . . . . . . 2
3. Opportunities and Limitations . . . . . . . . . . . . . . . . 3
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . 4
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 4
7.1. Normative References . . . . . . . . . . . . . . . . . . 4
7.2. Informative References . . . . . . . . . . . . . . . . . 5
Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 5
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
The Border Gateway Protocol (BGP) [RFC4271] has well-known
limitations in terms of the numbers of routes that can be carried and
the stability of the routing system. This is especially true for
routing systems that include mobile nodes that frequently change
their network attachment points, which in the past have resulted in
excessive announcements and withdrawals of de-aggregated prefixes.
This document discusses a means of accommodating scalable de-
aggregation of IPv6 prefixes [RFC8200] for overlay networks using
BGP.
2. Overview and Analysis
As discussed in [I-D.ietf-rtgwg-atn-bgp] and
[I-D.templin-intarea-6706bis], the method for accommodating scalable
de-aggregation is to institute an overlay network instance of BGP
that is separate and independent from the global Internet BGP routing
system. The overlay is presented to the global Internet as a small
number of aggregated IPv6 prefixes (also known as Mobility Service
Prefixes (MSPs)) that never change. In this way, the Internet BGP
routing system sees only stable aggregated MSPs (e.g., 2001:db8::/32)
and is completely unaware of any de-aggregation or mobility-related
churn that may be occurring within the overlay.
The overlay consists of a core Autonomous System (AS) with core AS
Border Routers (c-ASBRs) that connect to stub ASes with stub ASBRs
(s-ASBRs) in a hub-and-spokes fashion. Mobile nodes associate with
nearby (i.e., regional) s-ASBRs for extended timeframes, and change
to new s-ASBRs only after significant topological or geographic
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movements. Mobility-related changes between stub ASes are therefore
normally on a long-duration timescale.
The s-ASBRs use eBGP to announce de-aggregated Mobile Network
Prefixes (MNP) of mobile nodes (e.g., 2001:db8:1:2::/64) to their
neighboring c-ASBRs, but do not announce fine-grained mobility events
such as a mobile node moving to a new network attachment point.
Instead, mobile nodes coordinate with s-ASBRs using mobility
protocols such as MIPv6, LISP, AERO, etc. and s-ASBRs accommodate
these localized mobility events without disturbing the c-ASBRs.
The c-ASBRs originate "default" to their neighboring s-ASBRs but do
not announce any MNP routes. In this way, MNP announcements and
withdrawals are unidirectional from s-ASBRs to c-ASBRs only, thereby
suppressing BGP updates on the reverse path. The c-ASBRs in turn use
iBGP to maintain a consistent view of the full topology.
We expect that each c-ASBR should be able to carry at least as many
routes as can be carried by a typical core router in the global
public Internet BGP routing system. Since the number of active
routes in the Internet is quickly approaching 1 million (1M), we
therefore assume that each set of c-ASBRs can carry at least 1M MNP
routes which has been proven even for BGP running on lightweight
virtual machines. The method for increasing scaling therefore is to
divide the MSP into longer sub-MSPs, and to assign a different set of
c-ASBRs for each sub-MSP.
For example, the MSP 2001:db8::/32 could be sub-divided into sub-MSPs
such as 2001:db8:0010::/44, 2001:db8:0020::/44, 2001:db8:0030::/44,
etc. with each sub-MSP assigned to a different set of c-ASBRs. Each
s-ASBR peers with at least one member of each c-ASBR set and uses
route filters such that BGP updates are only sent to the c-ASBR(s)
that aggregate the specific sub-MSP. Then, assuming 1000 or more
sub-MSPs (each with its own set of c-ASBRs) the entire BGP overlay
routing system should be able to service 1 billion (1B) MSPs or more.
3. Opportunities and Limitations
Since a lightweight virtual machine (e.g., a Ubuntu linux image
running Quagga in the cloud) can service up to 1M MNPs using BGP, it
is conceivable that dedicated high-performance router hardware could
support even more - perhaps by a factor of 10 or more. With such
dedicated high-performance hardware, the numbers of MNPs that can be
serviced could be increased further.
The deployed numbers of s-ASBRs even for very large overlays should
not exceed the c-ASBR's capacity for BGP peering sessions. For
example, c-ASBRs should be capable of supporting a few thousands to a
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few tens of thousands of BGP peering sessions but it is not known
whether more could be supported.
By the same token, the maximum number of c-ASBR sets should be based
on the number of BGP peering sessions each s-ASBR can comfortably
accommodate, since each s-ASBR must peer with each c-ASBR set.
Packets sent between end systems that associate with different
s-ASBRs would initially need to be forwarded through the core AS,
which presents a forwarding bottleneck. For this reason, some form
of route optimization is needed to significantly reduce congestion in
the core and preferably to also allow for direct end system to end
system communications without involving s-ASBRs. Since c-ASBRs
should be standard commercial off-the-shelf (COTS) dedicated high-
performance IPv6 routers, however, they should not be required to
participate in any ancillary route optimization signaling. The AERO
route optimization function honors this design consideration.
Further opportunities and limitations are discussed in more detail in
the references [I-D.ietf-rtgwg-atn-bgp][I-D.templin-intarea-6706bis].
4. IANA Considerations
This document does not introduce any IANA considerations.
5. Security Considerations
Security considerations are discussed in the references.
6. 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.
7. References
7.1. 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>.
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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>.
7.2. Informative References
[I-D.ietf-rtgwg-atn-bgp]
Templin, F., Saccone, G., Dawra, G., Lindem, A., and V.
Moreno, "A Simple BGP-based Mobile Routing System for the
Aeronautical Telecommunications Network", draft-ietf-
rtgwg-atn-bgp-01 (work in progress), January 2019.
[I-D.templin-intarea-6706bis]
Templin, F., "Asymmetric Extended Route Optimization
(AERO)", draft-templin-intarea-6706bis-03 (work in
progress), December 2018.
Appendix A. Change Log
<< RFC Editor - remove prior to publication >>
Status as of 01/23/2018:
o -00 draft published
Author's Address
Fred L. Templin (editor)
Boeing Research & Technology
P.O. Box 3707
Seattle, WA 98124
USA
Email: fltemplin@acm.org
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