Address-Prefix-Based Outbound Route Filter for BGP-4
RFC 5292

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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],