draft-ietf-idr-bgp4-multiprotocol-v2-04.txt

BCAST Implementation for NS2

      +---------------------------------------------------------+



   The use and the meaning of these fields are as follows:

      Address Family Identifier:

         This field carries the identity of the Network Layer protocol
         associated with the NLRI that follows. Presently defined values
         for this field are specified in RFC1700 (see the Address Family
         Numbers section).

      Subsequent Address Family Identifier:

         This field provides additional information about the type of
         the Network Layer Reachability Information carried in the
         attribute.

      Withdrawn Routes:



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         A variable length field that lists NLRI for the routes that are
         being withdrawn from service. When the Subsequent Address
         Family Identifier field is set to one of the values defined in
         this document, each NLRI is encoded as specified in the "NLRI
         encoding" section of this document.

   An UPDATE message that contains the MP_UNREACH_NLRI is not required
   to carry any other path attributes.


6. NLRI encoding

   The Network Layer Reachability information is encoded as one or more
   2-tuples of the form <length, prefix>, whose fields are described
   below:


      +---------------------------+
      |   Length (1 octet)        |
      +---------------------------+
      |   Prefix (variable)       |
      +---------------------------+



   The use and the meaning of these fields are as follows:

      a) Length:

         The Length field indicates the length in bits of the address
         prefix. A length of zero indicates a prefix that matches all
         (as specified by the address family) addresses (with prefix,
         itself, of zero octets).

      b) Prefix:

         The Prefix field contains an address prefix followed by enough
         trailing bits to make the end of the field fall on an octet
         boundary.  Note that the value of trailing bits is irrelevant.












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7. Subsequent Address Family Identifier

   This document defines the following values for the Subsequent Address
   Family Identifier field carried in the MP_REACH_NLRI and
   MP_UNREACH_NLRI attributes:

      1 - Network Layer Reachability Information used for unicast
      forwarding

      2 - Network Layer Reachability Information used for multicast
      forwarding

      3 - Network Layer Reachability Information used for both unicast
      and multicast forwarding



8. Error Handling

   If a BGP speaker receives from a neighbor an Update message that
   contains the MP_REACH_NLRI or MP_UNREACH_NLRI attribute, and the
   speaker determines that the attribute is incorrect, the speaker must
   delete all the BGP routes received from that neighbor whose AFI/SAFI
   is the same as the one carried in the incorrect MP_REACH_NLRI or
   MP_UNREACH_NLRI attribute. For the duration of the BGP session over
   which the Update message was received, the speaker then should ignore
   all the subsequent routes with that AFI/SAFI received over that
   session.

   In addition, the speaker may terminate the BGP session over which the
   Update message was received. The session should be terminated with
   the Notification message code/subcode indicating "Update Message
   Error"/"Optional Attribute Error".


9. Use of BGP Capability Negotiation

   A BGP speaker that uses Multiprotocol Extensions should use the
   Capability Negotiation procedures [BGP-CAP] to determine whether the
   speaker could use Multiprotocol Extensions with a particular peer.

   The fields in the Capabilities Optional Parameter are set as follows.
   The Capability Code field is set to 1 (which indicates Multiprotocol
   Extensions capabilities). The Capability Length field is set to 4.
   The Capability Value field is defined as:


      The use and meaning of this field is as follow:



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                        0       7      15      23      31
                        +-------+-------+-------+-------+
                        |      AFI      | Res.  | SAFI  |
                        +-------+-------+-------+-------+

         AFI  - Address Family Identifier (16 bit), encoded the same way
         as in the Multiprotocol Extensions

         Res. - Reserved (8 bit) field. Should be set to 0 by the sender
         and ignored by the receiver.

         SAFI - Subsequent Address Family Identifier (8 bit), encoded
         the same way as in the Multiprotocol Extensions.

   A speaker that supports multiple <AFI, SAFI> tuples includes them as
   multiple Capabilities in the Capabilities Optional Parameter.

   To have a bi-directional exchange of routing information for a
   particular <AFI, SAFI> between a pair of BGP speakers, each such
   speaker must advertise to the other (via the Capability Negotiation
   mechanism) the capability to support that particular <AFI, SAFI>
   routes.


10. IANA Considerations

   As specified in this document, the MPL_REACH_NLRI and MP_UNREACH_NLRI
   attributes contain the Subsequence Address Family Identifier (SAFI)
   field.  SAFI value 0 is reserved. SAFI values 1, 2, and 3 are
   assigned in this document.  SAFI values 4 through 63 are to be
   assigned by IANA using the "IETF Consensus" policy defined in
   RFC2434. SAFI values 64 through 127 are to be assigned by IANA, using
   the "First  Come First Served" policy defined in RFC2434. SAFI values
   128 through 255 are vendor-specific, and values in this range are not
   to be assigned by IANA.















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11. Security Considerations

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


12. Acknowledgements

   The authors would like to thank members of the IDR Working Group for
   their review and comments.


13. References

   [BGP-CAP] "Capabilities Negotiation with BGP-4", R. Chandra, J.
   Scudder, draft-ietf-idr-bgp4-cap-neg-05.txt, February 1999

   [BGP-4] "A Border Gateway Protocol 4 (BGP-4)", Y. Rekhter & T. Li,
   RFC1771, March 1995

   [Heffernan]  Heffernan, A., "Protection of BGP Sessions via the TCP
   MD5 Signature Option", RFC2385, August 1998.

   [IPv4] "Internet Protocol", J. Postel, September 1981

   [RFC1700] "Assigned Numbers", J. Reynolds, J. Postel, RFC1700,
   October 1994 (see also http://www.iana.org/iana/assignments.html)


14. Author Information

   Tony Bates
   Cisco Systems, Inc.
   170 West Tasman Drive
   San Jose, CA 95134
   email: [e-mail]

   Ravi Chandra
   Siara Systems Incorporated
   1195 Borregas Avenue
   Sunnyvale, CA 94089
   e-mail: [e-mail]

   Dave Katz
   Juniper Networks, Inc.
   3260 Jay St.
   Santa Clara, CA 95054
   email: [e-mail]



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   Yakov Rekhter
   Cisco Systems, Inc.
   170 West Tasman Drive
   San Jose, CA 95134
   email: [e-mail]














































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