    Network Working Group                                           E. Chen
    Request for Comments: 5292                                    S. Sangli
    Category: Standards Track                                 Cisco Systems
                                                                August 2008

              Address-Prefix-Based Outbound Route Filter for BGP-4

    Status of This Memo

       This document specifies an Internet standards track protocol for the
       Internet community, and requests discussion and suggestions for
       improvements.  Please refer to the current edition of the "Internet
       Official Protocol Standards" (STD 1) for the standardization state
       and status of this protocol.  Distribution of this memo is unlimited.

    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.

    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>.

    Chen & Sangli               Standards Track                     [Page 1]

    RFC 5292           Address-Prefix-Based ORF for BGP-4        August 2008

       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 the 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 unspecified with
       a value of 0.

       The "Maxlen" field indicates the maximum prefix length (in bits) that
       is required for "matching".  The field is considered unspecified with
       a value of 0.

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

       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].

    Chen & Sangli               Standards Track                     [Page 2]

    RFC 5292           Address-Prefix-Based ORF for BGP-4        August 2008

    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 are 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.

    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 Network Layer Reachability Information (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.

    Chen & Sangli               Standards Track                     [Page 3]

    RFC 5292           Address-Prefix-Based ORF for BGP-4        August 2008

                 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 matches 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.

    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
       in [BGP-4].

    7.  Normative References

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

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

       [BGP-ORF] Chen, E., and Y. Rekhter, "Outbound Route Filtering
                 Capability for BGP-4", RFC 5291, August 2008.

    Chen & Sangli               Standards Track                     [Page 4]

    RFC 5292           Address-Prefix-Based ORF for BGP-4        August 2008

    Authors' Addresses

       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               Standards Track                     [Page 5]

    RFC 5292           Address-Prefix-Based ORF for BGP-4        August 2008

    Full Copyright Statement

       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
       "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
       OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
       THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
       OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
       THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
       WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

    Intellectual Property

       The IETF takes no position regarding the validity or scope of any
       Intellectual Property Rights or other rights that might be claimed to
       pertain to the implementation or use of the technology described in
       this document or the extent to which any license under such rights
       might or might not be available; nor does it represent that it has
       made any independent effort to identify any such rights.  Information
       on the procedures with respect to rights in RFC documents can be
       found in BCP 78 and BCP 79.

       Copies of IPR disclosures made to the IETF Secretariat and any
       assurances of licenses to be made available, or the result of an
       attempt made to obtain a general license or permission for the use of
       such proprietary rights by implementers or users of this
       specification can be obtained from the IETF on-line IPR repository at
       http://www.ietf.org/ipr.

       The IETF invites any interested party to bring to its attention any
       copyrights, patents or patent applications, or other proprietary
       rights that may cover technology that may be required to implement
       this standard.  Please address the information to the IETF at
       ietf-ipr@ietf.org.

    Chen & Sangli               Standards Track                     [Page 6]