datatracker.ietf.org
Sign in
Version 5.6.1.p1, 2014-07-16
Report a bug

BGP Support for Four-Octet Autonomous System (AS) Number Space
RFC 6793

Internet Engineering Task Force (IETF)                          Q. Vohra
Request for Comments: 6793                              Juniper Networks
Obsoletes: 4893                                                  E. Chen
Updates: 4271                                              Cisco Systems
Category: Standards Track                                  December 2012
ISSN: 2070-1721

     BGP Support for Four-Octet Autonomous System (AS) Number Space

Abstract

   The Autonomous System number is encoded as a two-octet entity in the
   base BGP specification.  This document describes extensions to BGP to
   carry the Autonomous System numbers as four-octet entities.  This
   document obsoletes RFC 4893 and updates RFC 4271.

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 5741.

   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/rfc6793.

Copyright Notice

   Copyright (c) 2012 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.

Vohra & Chen                 Standards Track                    [Page 1]
RFC 6793         BGP Support for 4-Octet AS Number Space   December 2012

1.  Introduction

   In the base BGP specification [RFC4271], the Autonomous System (AS)
   number is encoded as a two-octet entity.  To prepare for the
   anticipated exhaustion of the two-octet AS numbers, this document
   describes extensions to BGP to carry the AS numbers as four-octet
   entities.

   More specifically, this document defines a BGP capability code,
   "support for four-octet AS number capability", to be used by a BGP
   speaker to indicate its support for four-octet AS numbers.  Two
   attributes, AS4_PATH and AS4_AGGREGATOR, are introduced that can be
   used to propagate four-octet-based AS path information across BGP
   speakers that do not support four-octet AS numbers.  This document
   also specifies mechanisms for constructing the AS path information
   from the AS_PATH attribute and the AS4_PATH attribute.

   The extensions specified in this document allow a gradual transition
   from two-octet AS numbers to four-octet AS numbers.

   This document obsoletes RFC 4893 and updates RFC 4271.  It includes
   several clarifications and editorial changes, and it specifies the
   error handling for the new attributes.

2.  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 [RFC2119].

3.  Protocol Extensions

   For the purpose of this document, we define a BGP speaker that does
   not support the new four-octet AS number extensions as an OLD BGP
   speaker, and a BGP speaker that supports the new four-octet AS number
   extensions as a NEW BGP speaker.

   BGP carries the AS numbers in the "My Autonomous System" field of the
   OPEN message, in the AS_PATH attribute of the UPDATE message, and in
   the AGGREGATOR attribute of the UPDATE message.  BGP also carries the
   AS numbers in the BGP Communities attribute.

   A NEW BGP speaker uses BGP Capabilities Advertisements [RFC5492] to
   advertise to its neighbors (either internal or external) that it
   supports four-octet AS number extensions, as specified in this
   document.

Vohra & Chen                 Standards Track                    [Page 2]
RFC 6793         BGP Support for 4-Octet AS Number Space   December 2012

   The capability that is used by a BGP speaker to convey to its BGP
   peer the four-octet Autonomous System number capability also carries
   the AS number (encoded as a four-octet entity) of the speaker in the

[include full document text]