Network Working Group D. Rao
Internet-Draft Cisco Systems
Intended status: Standards Track P. Mohapatra
Expires: June 4, 2017 Sproute Networks
J. Haas
Juniper Networks, Inc.
December 1, 2016
Generic Subtype for BGP Four-octet AS specific extended community
draft-ietf-idr-as4octet-extcomm-generic-subtype-10
Abstract
Maintaining the current best practices with communities, ISPs and
enterprises that are assigned a 4-octet AS number may want the BGP
UPDATE messages they receive from their customers or peers to include
a 4-octet AS specific BGP extended community. This document defines
a new sub-type within the four-octet AS specific extended community
to facilitate this practice.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" are to
be interpreted as described in [RFC2119] only when they appear in all
upper case. They may also appear in lower or mixed case as English
words, without normative meaning.
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 http://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 June 4, 2017.
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Copyright Notice
Copyright (c) 2016 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
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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. Generic Sub-type Definition . . . . . . . . . . . . . . . . . 3
3. Deployment Considerations . . . . . . . . . . . . . . . . . . 4
4. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 4
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
6. Security Considerations . . . . . . . . . . . . . . . . . . . 5
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
7.1. Normative References . . . . . . . . . . . . . . . . . . 5
7.2. Informative References . . . . . . . . . . . . . . . . . 5
Appendix A. Document History . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
Maintaining the current best practices with communities, ISPs and
enterprises that are assigned a 4-octet AS number may want the BGP
UPDATE messages they receive from their customers or peers to include
a 4-octet AS specific extended community. This document defines a
new sub-type within the four-octet AS specific extended community to
facilitate this practice.
For example, [RFC1998] describes an application of BGP community
attribute ([RFC1997]) to implement flexible routing policies for
sites multi-homed to one or multiple providers. In a two-octet AS
environment, the advertised routes are usually associated with a
community attribute that encodes the provider's AS number in the
first two octets of the community and a LOCAL_PREF value in the
second two octets of the community. The community attribute signals
the provider edge routers connected to the site to set the
corresponding LOCAL_PREF on their advertisements to the IBGP mesh.
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In this way, customers can put into practice topologies like active-
backup.
When such a provider is assigned a four-octet AS number, the existing
mechanism of using communities is not sufficient since the AS portion
of the RFC 1997 community cannot exceed two bytes. The natural
alternative is to extend the same mechanism using extended
communities since it allows for encoding eight bytes of information.
[RFC5668] defines a format for a four-octet AS specific extended
community with a designated type field. That document defines two
sub-types: Four-octet specific Route Target extended community and
Four-octet specific Route Origin extended community. This document
specifies a generic sub-type for the four-octet AS specific extended
community to provide benefits such as the one cited above as the
Internet migrates to four-octet AS space.
2. Generic Sub-type Definition
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0x02 or 0x42 | 0x04 | Global |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Administrator | Local Administrator |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
This is an extended type with Type Field comprising of 2 octets and
Value Field comprising of 6 octets.
The high-order octet of this extended type is set to either 0x02 (for
transitive communities) or 0x42 (for non-transitive communities).
The low-order octet or the sub-type is set to 0x04.
The Value Field consists of two sub-fields:
Global Administrator sub-field: 4 octets
This sub-field contains a four-octet Autonomous System number.
Local Administrator sub-field: 2 octets
This sub-field contains a value that can influence routing
policies. This value has semantics that are of significance
for the Autonomous System in the Global Administrator field.
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3. Deployment Considerations
There are situations in peering where a 4-octet AS specific generic
extended community cannot be used.
A speaker with a 4-octet AS may not support 4-octet extended
communities; or the speaker may have a customer or peer that does not
support 4-octet extended communities. In all such cases, the speaker
may need to define an appropriate standard community value for the
same purpose. As an example, a peer may tag its routes with a
community that encodes AS_TRANS [RFC4893] as the first two octets.
Similarly, as per [RFC4893], a 2-octet Autonomous System number can
be converted into a 4-octet Autonomous System number by setting the
two high-order octets of the 4-octet field to zero. As a
consequence, at least in principle, an Autonomous System that has a
2-octet AS number could use either a standard community or the
4-octet AS specific generic extended community. This is undesirable,
as they would be treated as different communities, even if they had
the same values.
Therefore, for backward compatibility with existing deployments and
to avoid inconsistencies between standard communities and 4-octet
extended communities, Autonomous Systems that use 2-octet Autonomous
System numbers SHOULD use standard 2-octet communities as defined in
RFC1997 rather than the 4-octet AS specific extended community as
defined in this document.
4. Acknowledgments
The authors would like to thank Paul Jakma, Bruno Decraene and Cayle
Spandon for their useful comments on the document.
5. IANA Considerations
Prior revisions of this document requested IANA to make assignments
from the Transitive Four-Octet AS Specific Extended Community Sub-
Type registry and the Non-Transitive Four-Octet AS Specific Extended
Community Sub-Type registry. The sub-type value of 0x04 in each of
those registries was previously assigned:
Name Value
---- -----
transitive generic four-octet AS specific 0x0204
non-transitive generic four-octet AS specific 0x4204
IANA is requested to deprecate these assignments.
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6. Security Considerations
There are no additional security risks introduced by this design.
7. References
7.1. Normative 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>.
[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>.
[RFC4893] Vohra, Q. and E. Chen, "BGP Support for Four-octet AS
Number Space", RFC 4893, DOI 10.17487/RFC4893, May 2007,
<http://www.rfc-editor.org/info/rfc4893>.
[RFC5668] Rekhter, Y., Sangli, S., and D. Tappan, "4-Octet AS
Specific BGP Extended Community", RFC 5668,
DOI 10.17487/RFC5668, October 2009,
<http://www.rfc-editor.org/info/rfc5668>.
7.2. Informative References
[]
Heitz, J., Snijders, J., Patel, K., Bagdonas, I., and N.
Hilliard, "BGP Large Communities", draft-ietf-idr-large-
community-09 (work in progress), November 2016.
[RFC1998] Chen, E. and T. Bates, "An Application of the BGP
Community Attribute in Multi-home Routing", RFC 1998,
DOI 10.17487/RFC1998, August 1996,
<http://www.rfc-editor.org/info/rfc1998>.
Appendix A. Document History
This final version of the document exists only to request IANA to
deprecate its prior Extended Community assignments and provide a
historical record of the reason.
During the development of the BGP Four-octet feature [RFC4893],
operators had offered their commentarythat parity was needed with
existing BGP Community practices similar to those defined in
[RFC1998]. What became clear over time was that some operators
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encoded an AS number as the second field of their community;
essentially, as the "target".
Since an Extended Community's Local Administrator field cannot encode
more than two octets of value, the Extended Community format was not
appropriate for addressing parity of existing operational practices.
The BGP Large Communities Feature [I-D.ietf-idr-large-community]
supplanted the work begun in this document.
Authors' Addresses
Dhananjaya Rao
Cisco Systems
170 W. Tasman Drive
San Jose, CA 95134
USA
Email: dhrao@cisco.com
Pradosh Mohapatra
Sproute Networks
Email: mpradosh@yahoo.com
Jeffrey Haas
Juniper Networks, Inc.
1133 Innovation Way
Sunnyvale, CA 94089
US
Email: jhaas@juniper.net
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