Extended Optional Parameters Length for BGP OPEN Message
draft-ietf-idr-ext-opt-param-07

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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: February 1, 2020                                  July 31, 2019

        Extended Optional Parameters Length for BGP OPEN Message
                    draft-ietf-idr-ext-opt-param-07

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 also extended.

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on February 1, 2020.

Copyright Notice

   Copyright (c) 2019 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
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents

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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.  Since BGP Capabilities [RFC5492] are carried in the Optional
   Parameters field, and new BGP capabilities continue to be introduced,
   the limitation is 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 also extended.  This is done by
   using Optional Parameter Type 255 as a distinguished value, that
   indicates 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, an
   implementation MUST be prepared to accept an OPEN message that uses
   the encoding of this specification for Optional Parameters of any
   length.

   If the length of Optional Parameters is greater than 255, the
   extended encoding defined here MUST be used.  The (non-extended)
   length field MUST be set to 255.  The subsequent octet (which would
   be the first Optional Parameter Type in the non-extended format) MUST
   be set to 255 as well.  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

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   the given fields, there is no change to the BGP OPEN message defined
   in [RFC4271].

   When receiving an OPEN, a BGP speaker determines the extended
   encoding is in use if the first Optional Parameter Type field is 255.