Internet Engineering Task Force Z. Zhang, Ed. Internet-Draft Cisco Systems Intended status: Standards Track J. Qin, Ed. Expires: September 23, 2009 ZTE March 22, 2009 Border Gateway Protocol(BGP) AS_PATH Fragmenting draft-qin-idr-aspath-fragment-00 Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. 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. This Internet-Draft will expire on September 23, 2009. Copyright Notice Copyright (c) 2009 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents in effect on the date of publication of this document (http://trustee.ietf.org/license-info). Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Abstract This document discusses the issues of processing the AS_PATH attribute which provides sufficient information for constructing a Zhang & Qin Expires September 23, 2009 [Page 1] Internet-Draft AS_PATH Fragmenting March 2009 graph of AS connectivity, and defines the detailed procedure of fragmenting or merging a sequence of AS PATH segments. This is necessary for the robust implementation of Border Gateway Protocol (BGP) and the interoperation of vendors. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Requirements Language . . . . . . . . . . . . . . . . . . . 3 2. Attribute Processing . . . . . . . . . . . . . . . . . . . . . 3 3. Error Handing . . . . . . . . . . . . . . . . . . . . . . . . . 4 4. Implementation Recommendations . . . . . . . . . . . . . . . . 4 5. AS Confederations Considerations . . . . . . . . . . . . . . . 4 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4 7. Security Considerations . . . . . . . . . . . . . . . . . . . . 4 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 5 8.1. Normative References . . . . . . . . . . . . . . . . . . . 5 8.2. Informative References . . . . . . . . . . . . . . . . . . 5 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 5 Zhang & Qin Expires September 23, 2009 [Page 2] Internet-Draft AS_PATH Fragmenting March 2009 1. Introduction The Border Gateway Protocol (BGP) is an inter-Autonomous System routing protocol. And the AS_PATH attribute identifies the list of Autonomous Systems (ASes) through which routing information carried in UPDATE messages has passed. If the list of ASes exceeds length limit, the fragmentation of AS PATH segments has to be dealt with, and the reasonable operation is needed. This document defines the detailed procedure of fragmenting or merging a sequence of AS PATH segments. This is necessary for the robust implementation of Border Gateway Protocol (BGP) and the interoperation of vendors. 1.1. Requirements Language 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 RFC 2119 [RFC2119]. 2. Attribute Processing When BGP speaker modifies the route's AS_PATH attribute received or adds the AS_PATH attribute to the newly originated route, the basic procedure should be followed according to RFC4271. The local system MAY include/prepend more than one instance of its own AS number in the AS_PATH attribute. This operation is controlled via local configuration. Whenas the overflow happens due to the act of prepending AS numbers to the path segment, then: o If the available positions in the path segment of type AS_SEQUENCE are not enough for the AS numbers to be included, it SHOULD first fullfill the segment (255 totally), then prepend a new segment of type AS_SEQUENCE, and include the remaining AS numbers in the new segment. This operation MAY be repeated and more than one new segment MAY be created if the the AS numbers to be included are too many. The newer segment SHALL always be set as the first one of the AS_PATH. o When the local system creates a path segment of type AS_SET, and if the AS numbers to be included exceed 255, it SHOULD first fullfill the segment (255 totally), then prepend a new segment of type AS_SET, and include the remaining AS numbers in the new segment. This operation MAY be repeated and more than one new segment MAY be created if the the AS numbers to be included are too many. If multiple path segments are received, the local system SHOULD get them merged and refragmented (if needed) according to the procedure Zhang & Qin Expires September 23, 2009 [Page 3] Internet-Draft AS_PATH Fragmenting March 2009 discussed above unless all of the segments have been fullfilled. Whenever the local system performs fragmenting or merging, the correct order of the AS_PATH elements MUST be assured. 3. Error Handing The AS_PATH is checked for syntactic correctness. The path segment value contains one or more As numbers matching exactly the length field in the segment. If the check determines this is not the case, the Error Subcode MUST be set to Malformed AS_PATH. The AS_PATH contains one or more path segments of type AS_SEQUENCE and/or AS_SET but only one or one piece of continuous path segments of type AS_SET is allowed and MUST be placed at the end. If the check determines this is not the case, the Error Subcode MUST be set to Malformed AS_PATH. For the robust implementation of BGP, it SHOULD have the capability of fragmenting the path segment of the AS_PATH when overflow happens, besides correctly checking the multiple segments orderly to structure the graph of the AS_PATH. 4. Implementation Recommendations when the UPDATE message is built, and if the total length of the attribute exceeds size limit due to prepending too many fragmented path segments, an overload error notice MAY be sent up to the local system with the relevant prefix listed in the notice. 5. AS Confederations Considerations TBD. 6. IANA Considerations This memo includes no request to IANA. 7. Security Considerations It SHOULD rely on the authentication mechanisms oringinally defined Zhang & Qin Expires September 23, 2009 [Page 4] Internet-Draft AS_PATH Fragmenting March 2009 to solve the security problems. 8. References 8.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway Protocol 4 (BGP-4)", RFC 4271, January 2006. [RFC4893] Vohra, Q. and E. Chen, "BGP Support for Four-octet AS Number Space", RFC 4893, May 2007. [RFC5065] Traina, P., McPherson, D., and J. Scudder, "Autonomous System Confederations for BGP", RFC 5065, August 2007. [RFC5396] Huston, G. and G. Michaelson, "Textual Representation of Autonomous System (AS) Numbers", RFC 5396, December 2008. 8.2. Informative References [RFC2270] Stewart, J., Bates, T., Chandra, R., and E. Chen, "Using a Dedicated AS for Sites Homed to a Single Provider", RFC 2270, January 1998. [RFC4276] Hares, S. and A. Retana, "BGP-4 Implementation Report", RFC 4276, January 2006. Authors' Addresses Zhifeng Zhang (editor) Cisco Systems Beijing, P.R.C Phone: +86 10 8515 5569 Email: zhifzhan@cisco.com Zhang & Qin Expires September 23, 2009 [Page 5] Internet-Draft AS_PATH Fragmenting March 2009 Jacni Qin (editor) ZTE Shanghai, P.R.C Phone: +86 21 6889 6825 Email: jacniq@gmail.com Zhang & Qin Expires September 23, 2009 [Page 6]