Network Working Group Enke Chen
Internet Draft Redback Networks
Expiration Date: November 2004 Srihari R. Sangli
Procket Networks
Address Prefix Based Outbound Route Filter for BGP-4
draft-chen-bgp-prefix-orf-07.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.
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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.
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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
<Sequence, Match, Length, Prefix, Minlen, Maxlen>.
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.
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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.
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Internet Draft draft-chen-bgp-prefix-orf-07.txt May 2004
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 <length, prefix>.
The route is considered as "no match" to the ORF entry if the NLRI is
neither more specific than, nor equal to, the <Length, Prefix> fields
of the ORF entry.
When the NLRI is either more specific than, or equal to, the <Length,
Prefix> 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.
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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-10.txt, March
2004.
9. Author Information
Enke Chen
Redback Networks, Inc.
300 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
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