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Internet Engineering Task Force (IETF) J. Heitz, Ed.
Request for Comments: 8092 Cisco
Category: Standards Track J. Snijders, Ed.
ISSN: 2070-1721 NTT
K. Patel
Arrcus
I. Bagdonas
Equinix
N. Hilliard
INEX
February 2017
BGP Large Communities Attribute
Abstract
This document describes the BGP Large Communities attribute, an
extension to BGP-4. This attribute provides a mechanism to signal
opaque information within separate namespaces to aid in routing
management. The attribute is suitable for use with all Autonomous
System Numbers (ASNs) including four-octet ASNs.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc8092.
Heitz, et al. Standards Track [Page 1]
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RFC 8092 BGP Large Communities February 2017
Copyright Notice
Copyright (c) 2017 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
(http://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. Requirements Language ...........................................3
3. BGP Large Communities Attribute .................................3
4. Aggregation .....................................................4
5. Canonical Representation ........................................4
6. Error Handling ..................................................5
7. Security Considerations .........................................5
8. IANA Considerations .............................................6
9. References ......................................................6
9.1. Normative References .......................................6
9.2. Informative References .....................................6
Acknowledgments ....................................................7
Contributors .......................................................7
Authors' Addresses .................................................8
1. Introduction
BGP [RFC4271] implementations typically support a routing policy
language to control the distribution of routing information. Network
operators attach BGP communities to routes to associate particular
properties with these routes. These properties may include
information such as the route origin location, or specification of a
routing policy action to be taken, or one that has been taken, and is
applied to all routes contained in a BGP Update Message where the
Communities Attribute is included. Because BGP communities are
optional transitive BGP attributes, BGP communities may be acted upon
or otherwise used by routing policies in other Autonomous Systems
(ASes) on the Internet.
Heitz, et al. Standards Track [Page 2]
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RFC 8092 BGP Large Communities February 2017
A BGP Communities attribute is a variable-length attribute consisting
of a set of one or more four-octet values, each of which specify a
community [RFC1997]. Common use of the individual values of this
attribute type split this single 32-bit value into two 16-bit values.
The most significant word is interpreted as an Autonomous System
Number (ASN), and the least significant word is a locally defined
value whose meaning is assigned by the operator of the AS in the most
significant word.
Since the adoption of four-octet ASNs [RFC6793], the BGP Communities
attribute can no longer accommodate the above encoding, as a two-
octet word cannot fit a four-octet ASN. The BGP Extended Communities
attribute [RFC4360] is also unsuitable. The six-octet length of the
Extended Community value precludes the common operational practice of
encoding four-octet ASNs in both the Global Administrator and the
Local Administrator sub-fields.
To address these shortcomings, this document defines a BGP Large
Communities attribute encoded as an unordered set of one or more
twelve-octet values, each consisting of a four-octet Global
Administrator field and two four-octet operator-defined fields, each
of which can be used to denote properties or actions significant to
the operator of the AS assigning the values.
2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
3. BGP Large Communities Attribute
This document defines the BGP Large Communities attribute as an
optional transitive path attribute of variable length. All routes
with the BGP Large Communities attribute belong to the communities
specified in the attribute.
Heitz, et al. Standards Track [Page 3]
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RFC 8092 BGP Large Communities February 2017
Each BGP Large Community value is encoded as a 12-octet quantity, as
follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Global Administrator |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Local Data Part 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Local Data Part 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Global Administrator: A four-octet namespace identifier.
Local Data Part 1: A four-octet operator-defined value.
Local Data Part 2: A four-octet operator-defined value.
The Global Administrator field is intended to allow different ASes to
define BGP Large Communities without collision. This field SHOULD be
an ASN, in which case the Local Data Parts are to be interpreted as
defined by the owner of the ASN. The use of Reserved ASNs (0
[RFC7607], 65535 and 4294967295 [RFC7300]) is NOT RECOMMENDED.
There is no significance to the order in which twelve-octet Large
Community Attribute values are encoded in a Large Communities
attribute, A BGP speaker can transmit them in any order.
Duplicate BGP Large Community values MUST NOT be transmitted. A
receiving speaker MUST silently remove redundant BGP Large Community
values from a BGP Large Community attribute.
4. Aggregation
If a range of routes is aggregated, then the resulting aggregate
should have a BGP Large Communities attribute that contains all of
the BGP Large Communities attributes from all of the aggregated
routes.
5. Canonical Representation
The canonical representation of BGP Large Communities is three
separate unsigned integers in decimal notation in the following
order: Global Administrator, Local Data 1, Local Data 2. Numbers
MUST NOT contain leading zeros; a zero value MUST be represented with
a single zero. Each number is separated from the next by a single
colon. For example: 64496:4294967295:2, 64496:0:0.
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RFC 8092 BGP Large Communities February 2017
BGP Large Communities SHOULD be represented in the canonical
representation.
6. Error Handling
The error handling of BGP Large Communities is as follows:
o A BGP Large Communities attribute SHALL be considered malformed if
the length of the BGP Large Communities Attribute value, expressed
in octets, is not a non-zero multiple of 12.
o A BGP Large Communities attribute SHALL NOT be considered
malformed due to presence of duplicate Large Community values.
o A BGP UPDATE message with a malformed BGP Large Communities
attribute SHALL be handled using the approach of "treat-as-
withdraw" as described in Section 2 of [RFC7606].
The BGP Large Communities Global Administrator field may contain any
value, and a BGP Large Communities attribute MUST NOT be considered
malformed if the Global Administrator field contains an unallocated,
unassigned, or reserved ASN.
7. Security Considerations
This document does not change any underlying security issues
associated with any other BGP Communities mechanism. Specifically,
an AS relying on the BGP Large Communities attribute carried in BGP
must have trust in every other AS in the path, as any intermediate AS
in the path may have added, deleted, or altered the BGP Large
Communities attribute. Specifying the mechanism to provide such
trust is beyond the scope of this document.
BGP Large Communities do not protect the integrity of each community
value. Operators should be aware that it is possible for a BGP
speaker to alter BGP Large Community Attribute values in a BGP Update
Message. Protecting the integrity of the transitive handling of BGP
Large Community attributes in a manner consistent with the intent of
expressed BGP routing policies falls within the broader scope of
securing BGP, and is not specifically addressed here.
Network administrators should note the recommendations in Section 11
of "BGP Operations and Security" [RFC7454].
Heitz, et al. Standards Track [Page 5]
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RFC 8092 BGP Large Communities February 2017
8. IANA Considerations
IANA has assigned the value 32 (LARGE_COMMUNITY) in the "BGP Path
Attributes" subregistry under the "Border Gateway Protocol (BGP)
Parameters" registry.
9. References
9.1. 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,
<http://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,
<http://www.rfc-editor.org/info/rfc4271>.
[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,
<http://www.rfc-editor.org/info/rfc7606>.
9.2. Informative References
[RFC1997] Chandra, R., Traina, P., and T. Li, "BGP Communities
Attribute", RFC 1997, DOI 10.17487/RFC1997, August 1996,
<http://www.rfc-editor.org/info/rfc1997>.
[RFC4360] Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended
Communities Attribute", RFC 4360, DOI 10.17487/RFC4360,
February 2006, <http://www.rfc-editor.org/info/rfc4360>.
[RFC6793] Vohra, Q. and E. Chen, "BGP Support for Four-Octet
Autonomous System (AS) Number Space", RFC 6793,
DOI 10.17487/RFC6793, December 2012,
<http://www.rfc-editor.org/info/rfc6793>.
[RFC7300] Haas, J. and J. Mitchell, "Reservation of Last Autonomous
System (AS) Numbers", BCP 6, RFC 7300,
DOI 10.17487/RFC7300, July 2014,
<http://www.rfc-editor.org/info/rfc7300>.
[RFC7454] Durand, J., Pepelnjak, I., and G. Doering, "BGP Operations
and Security", BCP 194, RFC 7454, DOI 10.17487/RFC7454,
February 2015, <http://www.rfc-editor.org/info/rfc7454>.
Heitz, et al. Standards Track [Page 6]
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RFC 8092 BGP Large Communities February 2017
[RFC7607] Kumari, W., Bush, R., Schiller, H., and K. Patel,
"Codification of AS 0 Processing", RFC 7607,
DOI 10.17487/RFC7607, August 2015,
<http://www.rfc-editor.org/info/rfc7607>.
Acknowledgments
The authors would like to thank Ruediger Volk, Russ White, Acee
Lindem, Shyam Sethuram, Jared Mauch, Joel M. Halpern, Jeffrey Haas,
Gunter van de Velde, Marco Marzetti, Eduardo Ascenco Reis, Mark
Schouten, Paul Hoogsteder, Martijn Schmidt, Greg Hankins, Bertrand
Duvivier, Barry O'Donovan, Grzegorz Janoszka, Linda Dunbar, Marco
Davids, Gaurab Raj Upadhaya, Jeff Tantsura, Teun Vink, Adam
Davenport, Theodore Baschak, Pier Carlo Chiodi, Nabeel Cocker, Ian
Dickinson, Jan Baggen, Duncan Lockwood, David Farmer, Randy Bush, Wim
Henderickx, Stefan Plug, Kay Rechthien, Rob Shakir, Warren Kumari,
Gert Doering, Thomas King, Mikael Abrahamsson, Wesley Steehouwer,
Sander Steffann, Brad Dreisbach, Martin Millnert, Christopher Morrow,
Jay Borkenhagen, Arnold Nipper, Joe Provo, Niels Bakker, Bill Fenner,
Tom Daly, Ben Maddison, Alexander Azimov, Brian Dickson, Peter van
Dijk, Julian Seifert, Tom Petch, Tom Scholl, Arjen Zonneveld, Remco
van Mook, Adam Chappell, Jussi Peltola, Kristian Larsson, Markus
Hauschild, Richard Steenbergen, David Freedman, Richard Hartmann,
Geoff Huston, Mach Chen, and Alvaro Retana for their support,
insightful review, and comments.
Contributors
The following people contributed significantly to the content of the
document:
John Heasley
NTT Communications
Email: heas@shrubbery.net
Adam Simpson
Nokia
Email: adam.1.simpson@nokia.com
Heitz, et al. Standards Track [Page 7]
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RFC 8092 BGP Large Communities February 2017
Authors' Addresses
Jakob Heitz (editor)
Cisco
170 West Tasman Drive
San Jose, CA 95054
United States of America
Email: jheitz@cisco.com
Job Snijders (editor)
NTT Communications
Theodorus Majofskistraat 100
Amsterdam 1065 SZ
The Netherlands
Email: job@ntt.net
Keyur Patel
Arrcus, Inc.
Email: keyur@arrcus.com
Ignas Bagdonas
Equinix
80 Cheapside
London EC2V 6EE
United Kingdom
Email: ibagdona.ietf@gmail.com
Nick Hilliard
INEX
4027 Kingswood Road
Dublin 24
Ireland
Email: nick@inex.ie
Heitz, et al. Standards Track [Page 8]
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