RFC5668: 4-Octet AS Specific BGP Extended Community
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Related keywords:
(autonomous system)
(border gateway protocol)
Network Working Group Y. Rekhter
Request for Comments: 5668 Juniper Networks
Category: Standards Track S. Sangli
Cisco Systems
D. Tappan
Consultant
October 2009
4-Octet AS Specific BGP Extended Community
Abstract
This document defines a new type of a BGP extended community, which
carries a 4-octet Autonomous System (AS) number.
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
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Rekhter, et al. Standards Track [Page 1]
RFC 5668 4-Octet AS Specific Extended Community October 2009
not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other
than English.
1. Introduction
This document defines a new type of BGP extended community [RFC4360]:
a 4-octet AS specific extended community. This type of extended
community is similar to the 2-octet AS specific extended community,
except that it can carry a 4-octet Autonomous System number.
1.1. Specification of Requirements
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 RFC 2119 [RFC2119].
2. 4-Octet AS Specific Extended Community
This is an extended type with a Type field comprising 2 octets and a
Value field comprising 6 octets.
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 | Sub-Type | Global Administrator :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Global Administrator (cont.) | Local Administrator |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The value of the high-order octet of this extended type is either
0x02 (for transitive communities) or 0x42 (for non-transitive
communities). The low-order octet of this extended type is used to
indicate sub-types.
The Value field consists of 2 sub-fields:
Global Administrator sub-field: 4 octets
This sub-field contains a 4-octet Autonomous System number
assigned by IANA.
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RFC 5668 4-Octet AS Specific Extended Community October 2009
Local Administrator sub-field: 2 octets
The organization identified by the Autonomous System number in
the Global Administrator sub-field can encode any information
in this sub-field. The format and meaning of the value encoded
in this sub-field should be defined by the sub-type of the
community.
3. Considerations for 2-Octet Autonomous Systems
As per [RFC4893], a 2-octet Autonomous System number can be converted
into a 4-octet Autonomous System number by setting the 2 high-order
octets of the 4-octet field to zero.
As a consequence, at least in principle, an Autonomous System that
uses a 2-octet Autonomous System number could use either 2-octet or
4-octet AS specific extended communities. This is undesirable, as
both communities would be treated as different, even if they had the
same Sub-Type and Local Administrator values.
Therefore, for backward compatibility with existing deployments and
to avoid inconsistencies between 2-octet and 4-octet specific
extended communities, Autonomous Systems that use 2-octet Autonomous
System numbers SHOULD use 2-octet AS specific extended communities
rather than 4-octet AS specific extended communities.
4. IANA Considerations
This document defines a class of extended communities, called 4-octet
AS specific extended communities, for which the IANA has created and
will maintain a registry entitled Four-octet AS Specific Extended
Community. All the communities in this class are of extended Types.
Future assignments are to be made using the "First Come First Served"
policy defined in [RFC5226]. The Type values for the transitive
communities of the 4-octet AS specific extended community class are
0x0200-0x02ff; for the non-transitive communities of that class, they
are 0x4200-0x42ff. Assignments consist of a name and the value.
This document makes the following assignments for the 4-octet AS
specific extended community:
Name Type Value
---- ----------
four-octet AS specific Route Target 0x0202
four-octet AS specific Route Origin 0x0203
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RFC 5668 4-Octet AS Specific Extended Community October 2009
5. Security Considerations
This document does not add new security issues. All the security
considerations for BGP extended communities apply here. At the time
that this document was written, there were significant efforts
underway to improve the security properties of BGP. For examples of
documents that have been produced up to this time of publication, see
[RFC4593] and [SIDR].
There is a potential serious issue if a malformed, optional
transitive attribute is received. This issue and the steps to avoid
it are discussed in [OPT_TRANS].
6. Acknowledgements
Thanks to Bruno Decraene for his contributions to this document.
7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[RFC4360] Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended
Communities Attribute", RFC 4360, February 2006.
[RFC4893] Vohra, Q. and E. Chen, "BGP Support for Four-octet AS
Number Space", RFC 4893, May 2007.
7.2. Informative References
[OPT_TRANS] Scudder, J., and E. Chen, "Error Handling for Optional
Transitive BGP Attributes", Work in Progress, April 2009.
[RFC4593] Barbir, A., Murphy, S., and Y. Yang, "Generic Threats to
Routing Protocols", RFC 4593, October 2006.
[SIDR] Lepinski, M. and S. Kent, "An Infrastructure to Support
Secure Internet Routing", Work in Progress, July 2009.
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RFC 5668 4-Octet AS Specific Extended Community October 2009
Authors' Addresses
Yakov Rekhter
Juniper Networks, Inc.
EMail: yakov@juniper.net
Srihari R. Sangli
Cisco Systems, Inc.
EMail: rsrihari@cisco.com
Dan Tappan
Boxborough MA
EMail: Dan.Tappan@Gmail.com
Rekhter, et al. Standards Track [Page 5]