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Versions: (draft-chen-bgp-ext-opt-param) 00 01 02 03 04 05

Internet Engineering Task Force                                  E. Chen
Internet-Draft                                             Cisco Systems
Updates: 4271 (if approved)                                   J. Scudder
Intended status: Standards Track                        Juniper Networks
Expires: December 30, 2016                                 June 28, 2016


        Extended Optional Parameters Length for BGP OPEN Message
                    draft-ietf-idr-ext-opt-param-05

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.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on December 30, 2016.

Copyright Notice

   Copyright (c) 2016 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



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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
   Optional Parameters Length field.

   Accordingly, when the length of Optional Parameters in the BGP OPEN
   message is greater than 255, the OPEN message format is modified as
   follows, repurposing the Optional Parameters Length field as well as
   the first Optional Parameter Type field to indicate the use of the
   extended format:

       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    |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |     My Autonomous System      |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |           Hold Time           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                         BGP Identifier                        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |Non-Ext OP Len.|Non-Ext OP Type|  Extended Opt. Parm. Length   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       |             Optional Parameters (variable)                    |
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The non-extended Optional Parameters Length field MUST be set to 255
   on transmission, and MUST be ignored on receipt once the use of the
   extended format is determined.

   The subsequent one-octet field, that in the non-extended format would
   be the first Optional Parameter Type field, MUST be set to 255 on
   transmission.  On receipt, a value of 255 for this field is the
   indication that the extended format is in use.

   In this extended encoding, the subsequent two-octet field, termed the
   Extended Optional Parameters Length field, is an unsigned integer
   indicating the total length of the Optional Parameters field in
   octets.  If the value of this field is zero, no Optional Parameters
   are present (this would never be expected to happen with the extended
   encoding, however).

   Likewise, in that situation the Optional Parameters encoding is
   modified to be the following:



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       0                   1                   2
       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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |  Parm. Type   |        Parameter Length       |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       ~            Parameter Value (variable)         ~
       |                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The rules for encoding Optional Parameters are unchanged with respect
   to those given in [RFC4271] other than the extension of the Parameter
   Length field to be a two-octet unsigned integer.

   In parsing an OPEN message, a BGP speaker MUST use the value of the
   one-octet "Optional Parameters Length" field and the value of the
   octet following it to determine the encoding of the Optional
   Parameters length, as well as the size of the "Parameter Length"
   field of the Optional Parameters.  If both values are 255, then the
   four-octet encoding described above is used for the Optional
   Parameters length.  Otherwise the encoding defined in [RFC4271] is
   used.

   This encoding is chosen for backward compatibility reasons -- a BGP
   speaker which has not been upgraded to support this specification may
   legitimately send Optional Parameters whose length equals exactly
   255, thus the Optional Parameters Length field alone is insufficient
   as an indicator.  However, such a speaker would never legitimately
   send an Optional Parameter whose type code is 255, since that value
   has been reserved by this specification.

3.  Errors

   If a BGP speaker supporting this specification (a "new speaker") is
   peering with one which does not (an "old speaker") no
   interoperability issues arise unless the new speaker needs to encode
   Optional Parameters whose length exceeds 255.  In that case, it will
   transmit an OPEN message which the old speaker will interpret as
   containing an Optional Parameter with type code 255.  Since by
   definition the old speaker will not recognize that type code, the old
   speaker may be expected to close the connection with a NOTIFICATION
   with an Error Code of OPEN Message Error and an Error Subcode of
   Unsupported Optional Parameters, according to Section 6.2 of
   [RFC4271].

   Although the above is the most likely error to be sent, it is not
   impossible that the old speaker might detect some other error first,
   such as a length error, depending on the details of the
   implementation.  In no case would the peering be expected to



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   establish successfully; the only question is which NOTIFICATION would
   be generated.

   We note that in any case, such a peering could not succeed, since by
   definition the extended length encoding would not be used by the new
   speaker unless the basic encoding was insufficient.

   Although the Optional Parameter Type code 255 is used in this
   specification as the indication that the extended encoding is in use,
   it is not a bonafide Optional Parameter Type in the usual sense, and
   MUST NOT be used other than as described above.  If encountered as an
   actual Optional Parameter Type code, it MUST be treated as an
   unrecognized Optional Parameter and handled according to [RFC4271]
   Section 6.2.

4.  IANA Considerations

   IANA is requested to designate BGP OPEN Optional Parameter Type code
   255 as the Extended Length type code.

5.  Security Considerations

   This extension to BGP does not change the underlying security issues
   inherent in the existing BGP [RFC4272].

6.  Acknowledgements

   The authors would like to thank Yakov Rekhter and Srihari Sangli for
   discussing various options to enlarge the Optional Parameters field.
   We would also like to thank Matthew Bocci, Jakob Heitz, Pradosh
   Mohapatra, Keyur Patel and Hannes Gredler for their valuable
   comments.

7.  References

7.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC4271]  Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
              Border Gateway Protocol 4 (BGP-4)", RFC 4271,
              DOI 10.17487/RFC4271, January 2006,
              <http://www.rfc-editor.org/info/rfc4271>.





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7.2.  Informative References

   [RFC4272]  Murphy, S., "BGP Security Vulnerabilities Analysis",
              RFC 4272, DOI 10.17487/RFC4272, January 2006,
              <http://www.rfc-editor.org/info/rfc4272>.

   [RFC5492]  Scudder, J. and R. Chandra, "Capabilities Advertisement
              with BGP-4", RFC 5492, DOI 10.17487/RFC5492, February
              2009, <http://www.rfc-editor.org/info/rfc5492>.

Authors' Addresses

   Enke Chen
   Cisco Systems

   Email: enkechen@cisco.com


   John Scudder
   Juniper Networks

   Email: jgs@juniper.net





























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