Network Working Group Pedro R. Marques
Internet Draft cisco Systems, Inc.
Expiration Date: May 1998
November 1997
BGP-4 Capabilities Negotiation for BGP Multiprotocol Extensions
draft-marques-bgp4-cap-mp-00.txt
Status of this Memo
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1. Abstract
This document defines the usage of the BGP-4 Capabilities Negotiation
parameter to negotiate the support for a particular Address Family,
Sub-address Family pair between BGP-4 speakers using BGP-4
Multiprotocol Extensions.
2. Overview
BGP-4 Multiprotocol Extensions [BGP-MP] define two optional non-
transitive attributes that enable BGP-4 to carry routing information
for multiple Network Layer protocols. Such attributes are ignored by
BGP-4 when unrecognized either because the peer doesn't implement or
is not configured to accept BGP-4 Multiprotocol Extensions or a given
(AFI, SAFI) pair.
The use of BGP-4 Capabilities Parameter [BGP-CAP] allows two peers to
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negotiate the set of (AFI, SAFI) combinations supported on a
particular peering relationship. This document defines a Capability
Code that can be used for this purpose.
3. MP Capability Code
BGP speakers that wish to negotiate the set of (AFI, SAFI) pairs
availiable on a particular peering should use the MP_EXT Capability
Code (Type 0x81, in hexadecimal). The high-order bit on this code is
set to 1 meaning that this Capability is marked as "Required".
The Capability Value associated with the code is a 32 bit value, in
network byte-order, defined as:
0 7 15 23 31
+-------+-------+-------+-------+
| AFI | Res. | SAFI |
+-------+-------+-------+-------+
The use and meaning of this fields is as follows:
AFI - Address Family Identifier (16 bit) as defined in [RFC-
1700].
Res. - Reserved (8 bit) field. Should be set to 0 by the sender
and ignored by the receiver.
SAFI - Subsequent Address Family Identifier (8 bit) field as
defined in [BGP-MP]
Each (AFI, SAFI) pair is encoded in the Capabilities Optional
Parameter of a BGP-4 OPEN message as a separate triple <MP_EXT
Capability Code, Capability Length, MP_EXT Capability Value>. This
allows the requester to identify which (AFI, SAFI) values are not
supported by the peer on the receipt of a Unsupported Capability
NOTIFICATION.
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4. Security Considerations
Security issues are not discussed in this document.
5. Acknowledgements
To be supplied.
6. References
[BGP-4] "A Border Gateway Protocol 4 (BGP-4)",
Y. Rekhter and T. Li, RFC1771, March 1995.
[BGP-CAP] "Capabilities Negotiation with BGP-4",
R. Chandra and J. Scudder, Internet Draft, August 1997.
<draft-ietf-idr-bgp4-cap-neg-00.txt>
[BGP-MP] "Multiprotocol Extensions for BGP-4",
T. Bates, R. Chandra, D. Katz, and Y. Rekhter,
Internet Draft, September 1997.
<draft-ietf-idr-bgp4-multiprotocol-01.txt>
[RFC1700] "Assigned Numbers",
J. Reynolds and J. Postel, RFC 1700, October 1994.
7. Author Information
Pedro R. Marques
cisco Systems, Inc.
170 West Tasman Drive
San Jose, CA 95134
email: roque@cisco.com
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