RFC3392 - Capabilities Advertisement with BGP-4

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Network Working Group R. Chandra

Request for Comments: 3392 Redback Networks

Obsoletes: 2842 J. Scudder

Category: Standards Track Cisco Systems

November 2002

Capabilities Advertisement with 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.

Copyright Notice

Copyright (C) The Internet Society (2002). All Rights Reserved.

Abstract

This document defines a new Optional Parameter, called Capabilities,

that is eXPected to facilitate the introdUCtion of new capabilities

in the Border Gateway Protocol (BGP) by providing graceful capability

advertisement without requiring that BGP peering be terminated.

This document obsoletes RFC2842.

1. Introduction

Currently BGP-4 requires that when a BGP speaker receives an OPEN

message with one or more unrecognized Optional Parameters, the

speaker must terminate BGP peering. This complicates introduction of

new capabilities in BGP.

2. Specification of Requirements

The key Words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",

"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this

document are to be interpreted as described in RFC2119 [RFC2119].

3. Overview of Operations

When a BGP speaker [BGP-4] that supports capabilities advertisement

sends an OPEN message to its BGP peer, the message MAY include an

Optional Parameter, called Capabilities. The parameter lists the

capabilities supported by the speaker.

A BGP speaker determines the capabilities supported by its peer by

examining the list of capabilities present in the Capabilities

Optional Parameter carried by the OPEN message that the speaker

receives from the peer.

A BGP speaker that supports a particular capability may use this

capability with its peer after the speaker determines (as described

above) that the peer supports this capability.

A BGP speaker determines that its peer doesn't support capabilities

advertisement, if in response to an OPEN message that carries the

Capabilities Optional Parameter, the speaker receives a NOTIFICATION

message with the Error Subcode set to Unsupported Optional Parameter.

In this case the speaker SHOULD attempt to re-establish a BGP

connection with the peer without sending to the peer the Capabilities

Optional Parameter.

If a BGP speaker that supports a certain capability determines that

its peer doesn't support this capability, the speaker MAY send a

NOTIFICATION message to the peer, and terminate peering (see Section

"Extensions to Error Handling" for more details). The Error Subcode

in the message is set to Unsupported Capability. The message SHOULD

contain the capability (capabilities) that causes the speaker to send

the message. The decision to send the message and terminate peering

is local to the speaker. If terminated, such peering SHOULD NOT be

re-established automatically.

4. Capabilities Optional Parameter (Parameter Type 2):

This is an Optional Parameter that is used by a BGP speaker to convey

to its BGP peer the list of capabilities supported by the speaker.

The parameter contains one or more triples <Capability Code,

Capability Length, Capability Value>, where each triple is encoded as

shown below:

+------------------------------+

Capability Code (1 octet)

+------------------------------+

Capability Length (1 octet)

+------------------------------+

Capability Value (variable)

+------------------------------+

The use and meaning of these fields are as follows:

Capability Code:

Capability Code is a one octet field that unambiguously

identifies individual capabilities.

Capability Length:

Capability Length is a one octet field that contains the length

of the Capability Value field in octets.

Capability Value:

Capability Value is a variable length field that is interpreted

according to the value of the Capability Code field.

BGP speakers SHOULD NOT include more than one instance of a

capability with the same Capability Code, Capability Length, and

Capability Value. Note however, that processing of multiple

instances of such capability does not require special handling, as

additional instances do not change the meaning of announced

capability.

BGP speakers MAY include more than one instance of a capability (as

identified by the Capability Code) with non-zero Capability Length

field, but with different Capability Value, and either the same or

different Capability Length. Processing of these capability

instances is specific to the Capability Code and MUST be described in

the document introducing the new capability.

5. Extensions to Error Handling

This document defines new Error Subcode - Unsupported Capability.

The value of this Subcode is 7. The Data field in the NOTIFICATION

message SHOULD list the set of capabilities that cause the speaker to

send the message. Each such capability is encoded the same way as it

would be encoded in the OPEN message.

6. IANA Considerations

This document defines a Capability Optional Parameter along with an

Capability Code field. IANA maintains the registry for Capability

Code values. Capability Code value 0 is reserved. Capability Code

values 1 through 63 are to be assigned by IANA using the "IETF

Consensus" policy defined in RFC2434. Capability Code values 64

through 127 are to be assigned by IANA, using the "First Come First

Served" policy defined in RFC2434. Capability Code values 128

through 255 are for "Private Use" as defined in RFC2434.

7. Security Considerations

This extension to BGP does not change the underlying security issues

inherent in the existing BGP [Heffernan].

8. Acknowledgements

The authors would like to thank members of the IDR Working Group for

their review and comments.

9. Comparison with RFC2842

In addition to several minor editorial changes, this document also

clarifies how to handle multiple instances of the same capability.

10. References

[BGP-4] Rekhter, Y. and T. Li, "A Border Gateway Protocol 4

(BGP-4)", RFC1771, March 1995.

[Heffernan] Heffernan, A., "Protection of BGP Sessions via the TCP

MD5 Signature Option", RFC2385, August 1998.

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate

Requirement Levels", BCP 14, RFC2119, March 1997.

11. Authors' Addresses

Ravi Chandra

Redback Networks Inc.

350, Holger Way

San Jose, CA 95134

EMail: rchandra@redback.com

John G. Scudder

Cisco Systems, Inc.

170 West Tasman Drive

San Jose, CA 95134

EMail: jgs@cisco.com

12. Full Copyright Statement

Copyright (C) The Internet Society (2002). All Rights Reserved.

This document and translations of it may be copied and furnished to

others, and derivative works that comment on or otherwise explain it

or assist in its implementation may be prepared, copied, published

and distributed, in whole or in part, without restriction of any

kind, provided that the above copyright notice and this paragraph are

included on all such copies and derivative works. However, this

document itself may not be modified in any way, such as by removing

the copyright notice or references to the Internet Society or other

Internet organizations, except as needed for the purpose of

developing Internet standards in which case the procedures for

copyrights defined in the Internet Standards process must be

followed, or as required to translate it into languages other than

English.

The limited permissions granted above are perpetual and will not be

revoked by the Internet Society or its successors or assigns.

This document and the information contained herein is provided on an

"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING

TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING

BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION

HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF

MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

Funding for the RFCEditor function is currently provided by the

Internet Society.

 
 
 
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