Internet Draft Network Working Group Ravi Chandra Internet Draft Cisco Systems Expiration Date: March 2000 John G. Scudder Internet Engineering Group, LLC Capabilities Negotiation with BGP-4 draft-ietf-idr-bgp4-cap-neg-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 Currently BGP-4 [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. This document defines new Optional Parameter, called Capabilities, that is expected to facilitate introduction of new capabilities in BGP by providing graceful capability negotiation without requiring that BGP peering be terminated. Chandra, Scudder [Page 1] Internet Draft draft-ietf-idr-bgp4-cap-neg-04.txt September 1999 3. Overview of Operations When a BGP speaker that supports capabilities negotiation 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 negotiation, 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. 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. 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, where each triple is encoded as shown below: +------------------------------+ | Capability Code (1 octet) | Chandra, Scudder [Page 2] Internet Draft draft-ietf-idr-bgp4-cap-neg-04.txt September 1999 +------------------------------+ | 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. A particular capability, as identified by its Capability Code, may occur more than once within the Optional Parameter. This document reserves Capability Codes 128-255 for vendor-specific applications. This document reserves value 0. Capability Codes (other than those reserved for vendor specific use) are assigned only by the IETF consensus process and IESG approval. Chandra, Scudder [Page 3] Internet Draft draft-ietf-idr-bgp4-cap-neg-04.txt September 1999 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 lists the set of capabilities that cause the speaker to send the message. Each such capability is encoded the same way as it was encoded in the received OPEN message. 6. Security Considerations This extension to BGP does not change the underlying security issues. 7. Acknowledgements The authors would like to thank members of the IDR Working Group for their review and comments. 8. References [BGP-4] Rekhter, Y., and T. Li, "A Border Gateway Protocol 4 (BGP- 4)", RFC 1771, March 1995. 9. Author Information Ravi Chandra Cisco Systems, Inc. 170 West Tasman Drive San Jose, CA 95134 e-mail: rchandra@cisco.com John G. Scudder Internet Engineering Group, LLC 122 S. Main, Suite 280 Ann Arbor, MI 48104 e-mail: jgs@ieng.com Chandra, Scudder [Page 4]