Extended Optional Parameters Length for BGP OPEN Message
draft-ietf-idr-ext-opt-param-06

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Document Type Active Internet-Draft (idr WG)
Last updated 2019-07-30 (latest revision 2019-07-26)
Replaces draft-chen-bgp-ext-opt-param
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Internet Engineering Task Force                                  E. Chen
Internet-Draft                                             Cisco Systems
Updates: 4271 (if approved)                                   J. Scudder
Intended status: Standards Track                        Juniper Networks
Expires: January 27, 2020                                  July 26, 2019

        Extended Optional Parameters Length for BGP OPEN Message
                    draft-ietf-idr-ext-opt-param-06

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 update RFC 4271 by extending 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 January 27, 2020.

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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 January 27, 2020                [Page 1]
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   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.

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 update [RFC4271] by extending 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, an
   extended encoding is used.  The (non-extended) length field is set to
   255, as is the subsequent octet that in the non-extended format would
   be the first Optional Parameter Type.  The subsequent 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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   When receiving an OPEN, a BGP speaker determines the extended
   encoding is in use if the first Optional Parameter Type field is 255.
   In this case, the BGP speaker MUST ignore the non-extended Optional
   Parameters Length field, and must instead rely on the Extended
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