wdiff draft-ietf-idr-deprecate-as-set-confed-set-01.txt draft-ietf-idr-deprecate-as-set-confed-set-02.txt

Network Working Group W. Kumari
Internet-Draft Google, Inc.
Obsoletes: 6472 (if approved) K. Sriram
Updates: 4271 5065 (if approved) L. Hannachi
Intended status: Standards Track USA NIST
Expires: May 1, 6, 2020 October 29, November 3, 2019

Deprecation of AS_SET and AS_CONFED_SET in BGP
draft-ietf-idr-deprecate-as-set-confed-set-01
draft-ietf-idr-deprecate-as-set-confed-set-02

Abstract

BCP 172 (i.e., RFC 6472) recommends not using AS_SET and
AS_CONFED_SET in the Border Gateway Protocol. This document advances
this recommendation to a standards requirement in BGP; it proscribes
the use of the AS_SET and AS_CONFED_SET types of path segments in the
AS_PATH. This is done to simplify the design and implementation of
BGP and to make the semantics of the originator of a route clearer.
This will also simplify the design, implementation, and deployment of
various BGP security mechanisms. This document (if approved) updates
RFC 4271 and RFC 5065 by eliminating AS_SET and AS_CONFED_SET types,
and obsoletes RFC 6472.

Status of This Memo

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

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This Internet-Draft will expire on May 1, 6, 2020.

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3
3. Recommendation to Network Operators Recommendations . . . . . . . . . . . . . . . . . . . . . . . 3
4. Updates to Existing RFCs . . . . . . . . . . . . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . 4
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 4
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
8.1. Normative References . . . . . . . . . . . . . . . . . . 5
8.2. Informative References . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6

1. Introduction

BCP 172 [RFC6472] makes a recommendation for not using AS_SET (see
[RFC4271]) and AS_CONFED_SET (see [RFC5065]) in the Border Gateway
Protocol (BGP). This document advances the BCP recommendation to a
standards requirement in BGP; it proscribes the use of the AS_SET and
AS_CONFED_SET types of path segments in the AS_PATH.

The AS_SET path segment in the AS_PATH attribute (Sections 4.3 and
5.1.2 of [RFC4271]) is created by a router that is performing route
aggregation and contains an unordered set of Autonomous Systems
(ASes) that the update has traversed. The AS_CONFED_SET path segment
(see [RFC5065]) in the AS_PATH attribute is created by a router that
is performing route aggregation and contains an unordered set of
Member AS Numbers in the local confederation that the update has
traversed. It is very similar to AS_SETs but is used within a
confederation.

By performing aggregation, a router is combining multiple existing
routes into a single new route. The aggregation together with the
use of AS_SET blurs the semantics of origin AS for the prefix being
announced. Therefore, the aggregation with AS_SET (or AS_CONFED_SET)
can cause operational issues, such as not being able to authenticate
a route origin for the aggregate prefix in new BGP security
technologies such as those that take advantage of X.509 extensions
for IP addresses and AS identifiers [RFC3779] [RFC6480] [RFC6811]

[RFC8205]. This in turn could result in reachability problems for
the aggregated prefix and its components (i.e., more-specific
prefixes). The aggregation as described above could also create
traffic engineering issues, because the precise path information for
the component prefixes are not preserved.

From analysis of past Internet routing data, it is apparent that
aggregation that involves AS_SETs is very seldom used in practice on
the public Internet [Analysis] and when it is used, it is often used
incorrectly -- only a single AS in the AS_SET are by far the most
common cases. Also, very often the same AS appears in the
AS_SEQUENCE and the AS_SET in the BGP update. The occurrence of
reserved AS numbers ([IANA-SP-ASN]) is also somewhat frequent.
Because the aggregation involving AS_SETs is very rarely used, the
reduction in table size provided by this is extremely small, and any
advantage thereof is outweighed by additional complexity in BGP. As
noted above, AS_SETs also pose impediments to implementation of new
BGP security technologies.

In the past, AS_SET had been used in a few rare cases to allow route
aggregation where two or more providers could form the same aggregate
prefix, using the exact match of the other's aggregate prefix in some
advertisement and configuring the aggregation differently elsewhere.
The key to configuring this correctly was to form the aggregate at
the border in the outbound BGP policy and omit prefixes from the AS
that the aggregate was being advertised to. The AS_SET therefore
allowed this practice without the loss of BGP's AS_PATH loop
protection. This use of AS_SET served a purpose that fell in line
with the original intended use. Without the use of AS_SET,
aggregates must always contain only less-specific prefixes (not less
than or equal to) and must never aggregate an exact match.

2. Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.

3. Recommendation Recommendations

BGP speakers conforming to Network Operators

Network operators MUST NOT generate any new announcements containing
AS_SETs or AS_CONFED_SETs. If they have already announced routes
with AS_SETs or AS_CONFED_SETs in them, then they MUST withdraw those
routes and re-announce routes for the component prefixes this document (i.e., the
more-specific routes subsumed by the previously aggregated route)
without AS_SETs or AS_CONFED_SETs in the updates. A sending router conformant BGP
speakers) MUST not NOT locally generate a BGP UPDATE with messages containing
AS_SET or AS_CONFED_SET. A
receiving router MUST treat the announced routes in a Conformant BGP speakers SHOULD NOT send BGP
UPDATE with messages containing AS_SET or AS_CONFED_SET AS_CONFED_SET. Upon receipt of
such messages, conformant BGP speakers SHOULD use the "Treat-as-
withdraw" error handling behavior as withdrawn routes. per [RFC7606].

If a network operator wishes to consider a BGP UPDATE messages with
AS_SET or AS_CONFED_SET (received from an external peer) for path
selection, they MAY have a feature (knob) in
the router their BGP speaker to opt
to do so. so on a per peer basis. The operator should understand the
full implications of choosing this option.

Route aggregation that was previously performed by proxy aggregation
without the use of AS_SETs There is still possible under some conditions.
When doing this, no knob
concerning locally generated BGP UPDATE messages, i.e., as stated
before a conformant BGP speaker must not locally generate BGP UPDATE
messages with AS_SET or AS_CONFED_SET.

Network operators MUST form the aggregate at the border NOT locally generate any new announcements
containing AS_SET or AS_CONFED_SET. If they have announced routes
with AS_SET or AS_CONFED_SET in
the outbound BGP policy them, then they SHOULD withdraw those
routes and omit any prefixes from the AS that re-announce routes for the aggregate is being advertised to. As with any change, or component prefixes
(i.e., the operator
should understand more-specific routes subsumed by the full implications of previously aggregated
route) without AS_SET or AS_CONFED_SET in the change. updates.

It is worth noting that new BGP security technologies (such as those
that take advantage of X.509 extensions for IP addresses and AS
identifiers [RFC3779] [RFC6480] [RFC6811] [RFC8205]) might not
support routes with AS_SETs/AS_CONFED_SETs AS_SET or AS_CONFED_SET in them, and may treat
routes containing them as infeasible even before the updated BGP in
this document is implemented.

4. Updates to Existing RFCs

This document eliminates deprecates the AS_SET (type 1) AS_PATH segment type 1, namely, AS_SET that
is specified in Section 4.3 of
from [RFC4271]. That is, in a future
specification BGP speakers conforming to this document (i.e.,
conformant BGP speakers) MUST NOT locally generate BGP UPDATE
messages containing AS_SET. Conformant BGP speakers SHOULD NOT send
BGP UPDATE messages containing AS_SET. Upon receipt of such
messages, conformant BGP -- one that would obsolete RFC 4271 -- the speakers SHOULD use
of AS_SET will not be specified. the "Treat-as-withdraw"
error handling behavior as per [RFC7606].

This document also eliminates deprecates the AS_CONFED_SET (type 4) AS_PATH segment
type 4, namely, from [RFC5065]. Conformant BGP speakers MUST NOT locally
generate BGP UPDATE messages containing AS_CONFED_SET. Conformant
BGP speakers SHOULD NOT send BGP UPDATE messages containing
AS_CONFED_SET. Upon receipt of such messages, conformant BGP
speakers SHOULD use the "Treat-as-withdraw" error handling behavior
as per [RFC7606].

Wherever mentions of AS_SET or AS_CONFED_SET that is specified occur in Section 3 [RFC4271] and
[RFC5065], appropriate modification or elimination of [RFC5065]. That is, the text must
be made in a future specification of Autonomous System Confederations for BGP
-- one RFCs that would obsolete RFC 5065 -- replace these RFCs, consistent with
the use deprecation of AS_CONFED_SET will
not be specified. AS_SET and AS_CONFED_SET.

5. Security Considerations

This document obsoletes the use of aggregation techniques that create
AS_SETs or AS_CONFED_SETs. Obsoleting these path segment types from
BGP and removal of the related code from implementations would
potentially decrease the attack surface for BGP. Deployments of new
BGP security technologies [RFC6480] [RFC6811] [RFC8205] benefit
greatly if AS_SET and AS_CONFED_SET are not used in BGP.

6. IANA Considerations

This document requires no IANA actions.

7. Acknowledgements

The authors would like to thank Jeffery Haas, John Heasley, Job
Snijders, Jared Mauch, Jakob Heitz, Keyur Patel, Douglas Montgomery,
Randy Bush, Susan Hares, John Scudder, Curtis Villamizar, Danny
McPherson, Chris Morrow, Tom Petch, Ilya Varlashkin, Enke Chen, Tony
Li, Florian Weimer, John Leslie, Paul Jakma, Rob Austein, Russ
Housley, Sandra Murphy, Steve Bellovin, Steve Kent, Steve Padgett,
Alfred Hoenes, and Alvaro Retana for comments and suggestions.

8. References

8.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.

[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>.

[RFC5065] Traina, P., McPherson, D., and J. Scudder, "Autonomous
System Confederations for BGP", RFC 5065,
DOI 10.17487/RFC5065, August 2007,
<https://www.rfc-editor.org/info/rfc5065>.

8.2. Informative References

[Analysis]
Hannachi, L. and K. Sriram, "Detailed analysis of AS_SETs
in BGP updates", NIST Robust Inter-domain Routing Project
Website , October 2019,
<https://www.nist.gov/sites/default/files/
documents/2019/10/23/detailed-as_set-analysis.txt>.

[IANA-SP-ASN]
"Special-Purpose Autonomous System (AS) Numbers",
<https://www.iana.org/assignments/iana-as-numbers-special-
registry/iana-as-numbers-special-registry.xhtml>.

[RFC3779] Lynn, C., Kent, S., and K. Seo, "X.509 Extensions for IP
Addresses and AS Identifiers", RFC 3779,
DOI 10.17487/RFC3779, June 2004,
<https://www.rfc-editor.org/info/rfc3779>.

[RFC6472] Kumari, W. and K. Sriram, "Recommendation for Not Using
AS_SET and AS_CONFED_SET in BGP", BCP 172, RFC 6472,
DOI 10.17487/RFC6472, December 2011,
<https://www.rfc-editor.org/info/rfc6472>.

[RFC6480] Lepinski, M. and S. Kent, "An Infrastructure to Support
Secure Internet Routing", RFC 6480, DOI 10.17487/RFC6480,
February 2012, <https://www.rfc-editor.org/info/rfc6480>.

[RFC6811] Mohapatra, P., Scudder, J., Ward, D., Bush, R., and R.
Austein, "BGP Prefix Origin Validation", RFC 6811,
DOI 10.17487/RFC6811, January 2013,
<https://www.rfc-editor.org/info/rfc6811>.

[RFC7606] Chen, E., Ed., Scudder, J., Ed., Mohapatra, P., and K.
Patel, "Revised Error Handling for BGP UPDATE Messages",
RFC 7606, DOI 10.17487/RFC7606, August 2015,
<https://www.rfc-editor.org/info/rfc7606>.

[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.

[RFC8205] Lepinski, M., Ed. and K. Sriram, Ed., "BGPsec Protocol
Specification", RFC 8205, DOI 10.17487/RFC8205, September
2017, <https://www.rfc-editor.org/info/rfc8205>.

Authors' Addresses

Warren Kumari
Google, Inc.
1600 Amphitheatre Parkway
Mountain View, CA 94043
US

Phone: +1 571 748 4373
Email: warren@kumari.net

Kotikalapudi Sriram
USA NIST
100 Bureau Drive
Gaithersburg, MD 20899
US

Phone: +1 301 975 3973
Email: sriram.ietf@gmail.com
Lilia Hannachi
USA NIST
100 Bureau Drive
Gaithersburg, MD 20899
US

Phone: +1 301 975 3259
Email: lilia.hannachi@nist.gov