Extended Optional Parameters Length for BGP OPEN Message
draft-ietf-idr-ext-opt-param-04

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Last updated 2016-03-14
Replaces draft-chen-bgp-ext-opt-param
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Internet Engineering Task Force                                  E. Chen
Internet-Draft                                             Cisco Systems
Intended status: Standards Track                              J. Scudder
Expires: September 15, 2016                             Juniper Networks
                                                          March 14, 2016

        Extended Optional Parameters Length for BGP OPEN Message
                    draft-ietf-idr-ext-opt-param-04

Abstract

   The Optional Parameters in the BGP OPEN message as defined in the
   base BGP specification are limited to 255 octets due to a one-octet
   length field.  BGP Capabilities are carried in this field and may
   foreseeably exceed 255 octets in the future, leading to concern about
   this limitation.

   In this document we extend the BGP OPEN length field in a backward-
   compatible manner.  The Parameter Length field of individual Optional
   Parameters is similarly extended.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on September 15, 2016.

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   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   publication of this document.  Please review these documents

Chen & Scudder         Expires September 15, 2016               [Page 1]
Internet-Draft     Extended Optional Parameters Length        March 2016

   carefully, as they describe your rights and restrictions with respect
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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.

1.  Introduction

   The Optional Parameters Length field in the BGP OPEN message is
   defined in the base BGP specification [RFC4271] as one octet, thus
   limiting the Optional Parameters field in the OPEN message to 255
   octets.  As BGP Capabilities [RFC5492] are carried in the Optional
   Parameters field, and new BGP capabilities continue to be introduced,
   the limitation is becoming a concern for BGP development.

   In this document we extend the BGP OPEN length field in a backward-
   compatible manner.  The Parameter Length field of individual Optional
   Parameters is similarly extended.  This is done by using Optional
   Parameters Length of 255 combined with Optional Parameter Type 255 as
   a distinguished value pair, which indicates that an extended Optional
   Parameters Length field follows.  In this case the Parameter Length
   field of the Optional Parameters in the BGP OPEN message is also
   extended.

1.1.  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 RFC 2119 [RFC2119].

2.  Protocol Extensions

   This document reserves Optional Parameter Type code 255 as the
   "Extended Length" type code.

   In the event that the length of Optional Parameters in the BGP OPEN
   message does not exceed 255, the encodings of the base BGP
   specification [RFC4271] MUST be used without alteration.

   However, if the length of Optional Parameters is greater than 255,
   four octets are used for the length field.  Each of the first two
   octets is set to 255, and the remaining two octets carry the actual
   length.  In addition, the "Parameter Length" field of each Optional
   Parameter is enlarged to two octets.  Other than the larger sizes of
   the given fields, there is no change to the BGP OPEN message defined
   in [RFC4271].

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   Accordingly, when the length of Optional Parameters in the BGP OPEN
   message is greater than 255, the OPEN message format is modified to
   be the following:

       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
       +-+-+-+-+-+-+-+-+
       |    Version    |
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