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Network Working Group                                           E. Chen
Internet Draft                                                S. Sangli
Expiration Date: January 2009                             Cisco Systems


          Address Prefix Based Outbound Route Filter for BGP-4

                  draft-ietf-idr-bgp-prefix-orf-05.txt


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Abstract

   This document defines a new Outbound Router Filter (ORF) type for
   BGP, termed "Address Prefix Outbound Route Filter", that can be used
   to perform address prefix based route filtering. This ORF-type
   supports prefix length or range based matching, wild-card based
   address prefix matching, as well as the exact address prefix matching
   for address families.










Chen & Sangli                                                   [Page 1]

Internet Draft    draft-ietf-idr-bgp-prefix-orf-05.txt         June 2008


1. Introduction

   The Outbound Route Filtering Capability defined in [BGP-ORF] provides
   a mechanism for a BGP speaker to send to its BGP peer a set of
   Outbound Route Filters (ORFs) that can be used by its peer to filter
   its outbound routing updates to the speaker.

   This documents defines a new ORF-type for BGP, termed "Address Prefix
   Outbound Route Filter (Address Prefix ORF)", that can be used to
   perform address prefix based route filtering. The Address Prefix ORF
   supports prefix length or range based matching, wild-card based
   address prefix matching, as well as the exact address prefix matching
   for address families [BGP-MP].


2. Address Prefix ORF-Type

   The Address Prefix ORF-Type allows one to express ORFs in terms of
   address prefixes. That is, it provides address prefix based route
   filtering, including prefix length or range based matching, as well
   as wild-card address prefix matching.

   Conceptually an Address Prefix ORF entry consists of the fields
   <Sequence, Match, Length, Prefix, Minlen, Maxlen>.

   The "Sequence" field specifies the relative ordering of the entry
   among all the Address Prefix ORF entries.

   The "Match" field specifies whether this entry is "PERMIT" (value 0),
   or "DENY" (value 1).

   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).

   The "Prefix" field contains an address prefix of an address family.

   The "Minlen" field indicates the minimum prefix length in bits that
   is required for "matching". The field is considered as un-specified
   with value 0.

   The "Maxlen" field indicates the maximum prefix length in bits that
   is required for "matching". The field is considered as un-specified
   with value 0.

   The fields "Sequence", "Length", "Minlen", and "Maxlen" are all
   unsigned integers.



Chen & Sangli                                                   [Page 2]

Internet Draft    draft-ietf-idr-bgp-prefix-orf-05.txt         June 2008


   This document imposes the following requirement on the values of
   these fields:

           0 <= Length < Minlen <= Maxlen

   However, tests related to the "Minlen" or "Maxlen" value should be
   omitted when the "Minlen" or "Maxlen" field (respectively) is
   unspecified.

   In addition, the "Maxlen" value must be no more than the maximum
   length (in bits) of a host address for a given address family [BGP-
   MP].


3. Address Prefix ORF Encoding

   The value of the ORF-Type for the Address Prefix ORF-Type is 64.

   An Address Prefix ORF entry is encoded as follows. The "Match" field
   of the entry is encoded in the "Match" field of the common part
   [BGP-ORF], and the remaining fields of the entry is encoded in the
   "Type specific part" as shown in Figure 1.


               +--------------------------------+
               |   Sequence (4 octets)          |
               +--------------------------------+
               |   Minlen   (1 octet)           |
               +--------------------------------+
               |   Maxlen   (1 octet)           |
               +--------------------------------+
               |   Length   (1 octet)           |
               +--------------------------------+
               |   Prefix   (variable length)   |
               +--------------------------------+

              Figure 1: Address Prefix ORF Encoding


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









Chen & Sangli                                                   [Page 3]

Internet Draft    draft-ietf-idr-bgp-prefix-orf-05.txt         June 2008


4. Address Prefix ORF Matching

   In addition to the general matching rules defined in [BGP-ORF],
   several Address Prefix ORF specific matching rules are defined as
   follows.

   Consider an Address Prefix ORF entry, and a route maintained by a BGP
   speaker with NLRI in the form of <Prefix, Length>.

   The route is considered as "no match" to the ORF entry if the NLRI is
   neither more specific than, nor equal to, the <Prefix, Length> fields
   of the ORF entry.

   When the NLRI is either more specific than, or equal to, the <Prefix,
   Length> fields of the ORF entry, the route is considered as a match
   to the ORF entry only if the NLRI match condition as listed in Table
   1 is satisfied.


              ORF Entry                  NLRI
         Minlen      Maxlen         Match Condition
       +------------------------------------------------------+
       | un-spec.    un-spec.       NLRI.length == ORF.length |
       +------------------------------------------------------+
       | specified   un-spec.       NLRI.length >= ORF.Minlen |
       +------------------------------------------------------+
       | un-spec.    specified      NLRI.length <= ORF.Maxlen |
       +------------------------------------------------------+
       | specified   specified      NLRI.length >= ORF.Minlen |
       |                        AND NLRI.length <= ORF.Maxlen |
       +------------------------------------------------------+

               Table 1: Address Prefix ORF Matching


   When more than one Address Prefix ORF entry match the NLRI of the
   route, the "first-match" rule applies. That is, the ORF entry with
   the smallest sequence number (among all the matching ORF entries) is
   considered as the sole match, and it would determine whether the
   route should be advertised.

   The assignment of the sequence numbers is a local matter for the BGP
   speaker that sends the Address Prefix ORF entries.








Chen & Sangli                                                   [Page 4]

Internet Draft    draft-ietf-idr-bgp-prefix-orf-05.txt         June 2008


5. IANA Considerations

   This document specifies a new Outbound Route Filtering (ORF) type,
   Address Prefix ORF. The value of the ORF-type is 64.


6. Security Considerations

   This extension to BGP does not change the underlying security issues
   [BGP-4].


7. Normative References

   [BGP-4] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway Protocol
   4 (BGP-4)", RFC 4271, January 2006.

   [BGP-MP] Bates, T., Chandra, R., Rekhter, Y., and D. Katz,
   "Multiprotocol Extensions for BGP-4", RFC 4760, January 2007.

   [BGP-ORF] Chen, E., and Rekhter, Y., "Outbound Route Filtering
   Capability for BGP-4", draft-ietf-idr-route-filter-17.txt, June 2008.


8. Author Information

   Enke Chen
   Cisco Systems, Inc.
   170 W. Tasman Dr.
   San Jose, CA 95134

   EMail: enkechen@cisco.com


   Srihari R. Sangli
   Cisco Systems, Inc.
   170 W. Tasman Dr.
   San Jose, CA 95134

   EMail: rsrihari@cisco.com











Chen & Sangli                                                   [Page 5]

Internet Draft    draft-ietf-idr-bgp-prefix-orf-05.txt         June 2008


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10. Full Copyright Notice

   Copyright (C) The IETF Trust (2008).

   This document is subject to the rights, licenses and restrictions
   contained in BCP 78, and except as set forth therein, the authors
   retain all their rights.

   This document and the information contained herein are provided on an
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   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.











Chen & Sangli                                                   [Page 6]


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