Network Working Group Enke Chen Internet Draft Redback Networks Expiration Date: October 2002 Srihari R. Sangli Procket Networks Address Prefix Based Outbound Route Filter for BGP-4 draft-chen-bgp-prefix-orf-04.txt 1. Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026 except that the right to produce derivative works is not granted. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. 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.'' The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. 2. Abstract This document defines a new Outbound Router Filter 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-chen-bgp-prefix-orf-04.txt April 2002 3. Introduction The Cooperative 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]. 4. 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 . The "Sequence" field is a number that specifies the relative ordering of the entry. 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-chen-bgp-prefix-orf-04.txt April 2002 This document imposes the following requirement on the values of these fields: 0 <= Length < Minlen <= Maxlen In addition, the "Maxlen" must be no more than the maximum length (in bits) of a host address for a given address family [BGP-MP]. 5. 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 follows. +--------------------------------+ | Sequence (4 octets) | +--------------------------------+ | Minlen (1 octet) | +--------------------------------+ | Maxlen (1 octet) | +--------------------------------+ | Length (1 octet) | +--------------------------------+ | Prefix (variable length) | +--------------------------------+ 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-chen-bgp-prefix-orf-04.txt April 2002 6. 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 . The route is considered as "no match" to the ORF entry if the NLRI is neither more specific than, nor equal to, the fields of the ORF entry. When the NLRI is either more specific than, or equal to, the 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 the following table is satisfied. ORF Entry NLRI Minlen Maxlen Match Condition +------------------------------------------------------+ | un-spec. un-spec. NLRI.legnth == 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 | +------------------------------------------------------+ It is possible that the speaker would have more than one Prefix Address ORF entry that matches the NLRI of the route. In that case 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. Chen & Sangli [Page 4] Internet Draft draft-chen-bgp-prefix-orf-04.txt April 2002 7. Security Considerations This extension to BGP does not change the underlying security issues. 8. References [BGP-4] Rekhter, Y., and T. Li, "A Border Gateway Protocol 4 (BGP- 4)", RFC 1771, March 1995. [BGP-MP] Bates, T., Chandra, R., Katz, D. and Y. Rekhter, "Multiprotocol Extensions for BGP-4", RFC 2858, June 2000. [BGP-ORF] Chen, E., and Rekhter, Y., "Cooperative Route Filtering Capability for BGP-4", draft-ietf-idr-route-filter-05.txt, January 2002. 9. Author Information Enke Chen Redback Networks, Inc. 350 Holger Way San Jose, CA 95134 email: enke@redback.com Srihari R. Sangli Procket Networks, Inc. 1100 Cadillac Court Milpitas, CA - 95035 e-mail: srihari@procket.com Chen & Sangli [Page 5]