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'BGP-4') (Obsoleted by RFC 4271) Summary: 7 errors (**), 0 flaws (~~), 2 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 Network Working Group Ravi Chandra 2 Internet Draft Cisco Systems 3 Expiration Date: March 2000 John G. Scudder 4 Internet Engineering Group, LLC 6 Capabilities Negotiation with BGP-4 8 draft-ietf-idr-bgp4-cap-neg-04.txt 10 1. Status of this Memo 12 This document is an Internet-Draft and is in full conformance with 13 all provisions of Section 10 of RFC2026 except that the right to 14 produce derivative works is not granted. 16 Internet-Drafts are working documents of the Internet Engineering 17 Task Force (IETF), its areas, and its working groups. Note that 18 other groups may also distribute working documents as Internet- 19 Drafts. 21 Internet-Drafts are draft documents valid for a maximum of six months 22 and may be updated, replaced, or obsoleted by other documents at any 23 time. It is inappropriate to use Internet-Drafts as reference 24 material or to cite them other than as ``work in progress.'' 26 The list of current Internet-Drafts can be accessed at 27 http://www.ietf.org/ietf/1id-abstracts.txt 29 The list of Internet-Draft Shadow Directories can be accessed at 30 http://www.ietf.org/shadow.html. 32 2. Abstract 34 Currently BGP-4 [BGP-4] requires that when a BGP speaker receives an 35 OPEN message with one or more unrecognized Optional Parameters, the 36 speaker must terminate BGP peering. This complicates introduction of 37 new capabilities in BGP. 39 This document defines new Optional Parameter, called Capabilities, 40 that is expected to facilitate introduction of new capabilities in 41 BGP by providing graceful capability negotiation without requiring 42 that BGP peering be terminated. 44 3. Overview of Operations 46 When a BGP speaker that supports capabilities negotiation sends an 47 OPEN message to its BGP peer, the message may include an Optional 48 Parameter, called Capabilities. The parameter lists the capabilities 49 supported by the speaker. 51 A BGP speaker determines the capabilities supported by its peer by 52 examining the list of capabilities present in the Capabilities 53 Optional Parameter carried by the OPEN message that the speaker 54 receives from the peer. 56 A BGP speaker that supports a particular capability may use this 57 capability with its peer after the speaker determines (as described 58 above) that the peer supports this capability. 60 A BGP speaker determines that its peer doesn't support capabilities 61 negotiation, if in response to an OPEN message that carries the 62 Capabilities Optional Parameter, the speaker receives a NOTIFICATION 63 message with the Error Subcode set to Unsupported Optional Parameter. 64 In this case the speaker should attempt to re-establish a BGP 65 connection with the peer without sending to the peer the Capabilities 66 Optional Parameter. 68 If a BGP speaker that supports a certain capability determines that 69 its peer doesn't support this capability, the speaker may send a 70 NOTIFICATION message to the peer, and terminate peering. The Error 71 Subcode in the message is set to Unsupported Capability. The message 72 should contain the capability (capabilities) that causes the speaker 73 to send the message. The decision to send the message and terminate 74 peering is local to the speaker. Such peering should not be re- 75 established automatically. 77 4. Capabilities Optional Parameter (Parameter Type 2): 79 This is an Optional Parameter that is used by a BGP speaker to convey 80 to its BGP peer the list of capabilities supported by the speaker. 82 The parameter contains one or more triples , where each triple is encoded as 84 shown below: 86 +------------------------------+ 87 | Capability Code (1 octet) | 88 +------------------------------+ 89 | Capability Length (1 octet) | 90 +------------------------------+ 91 | Capability Value (variable) | 92 +------------------------------+ 94 The use and meaning of these fields are as follows: 96 Capability Code: 98 Capability Code is a one octet field that unambiguously 99 identifies individual capabilities. 101 Capability Length: 103 Capability Length is a one octet field that contains the length 104 of the Capability Value field in octets. 106 Capability Value: 108 Capability Value is a variable length field that is interpreted 109 according to the value of the Capability Code field. 111 A particular capability, as identified by its Capability Code, may 112 occur more than once within the Optional Parameter. 114 This document reserves Capability Codes 128-255 for vendor-specific 115 applications. 117 This document reserves value 0. 119 Capability Codes (other than those reserved for vendor specific use) 120 are assigned only by the IETF consensus process and IESG approval. 122 5. Extensions to Error Handling 124 This document defines new Error Subcode - Unsupported Capability. 125 The value of this Subcode is 7. The Data field in the NOTIFICATION 126 message lists the set of capabilities that cause the speaker to send 127 the message. Each such capability is encoded the same way as it was 128 encoded in the received OPEN message. 130 6. Security Considerations 132 This extension to BGP does not change the underlying security issues. 134 7. Acknowledgements 136 The authors would like to thank members of the IDR Working Group for 137 their review and comments. 139 8. References 141 [BGP-4] Rekhter, Y., and T. Li, "A Border Gateway Protocol 4 (BGP- 142 4)", RFC 1771, March 1995. 144 9. Author Information 146 Ravi Chandra 147 Cisco Systems, Inc. 148 170 West Tasman Drive 149 San Jose, CA 95134 150 e-mail: rchandra@cisco.com 152 John G. Scudder 153 Internet Engineering Group, LLC 154 122 S. Main, Suite 280 155 Ann Arbor, MI 48104 156 e-mail: jgs@ieng.com