Network Working Group
Request for Comments: 5668
Category: Standards Track
Y. Rekhter
Juniper Networks
S. Sangli
Cisco Systems
D. Tappan
October 2009

4-Octet AS Specific BGP Extended Community


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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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.

      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

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.

Authors' Addresses

   Yakov Rekhter
   Juniper Networks, Inc.
   Srihari R. Sangli
   Cisco Systems, Inc.
   Dan Tappan
   Boxborough MA