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
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Chen & Sangli Standards Track [Page 6]
