Network Working Group Srihari Ramachandra Internet Draft Daniel Tappan Expiration Date: December 2000 cisco Systems BGP Extended Communities Attribute draft-ramachandra-bgp-ext-communities-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 This document describes an extension to BGP [BGP-4] which may be used to provide flexible control over the distribution of routing information. Ramachandra, Tappan [Page 1] Internet Draftdraft-ramachandra-bgp-ext-communities-04.txt May 2000 3. Introduction The Extended Community Attribute provides two important enhancements over the existing BGP Community Attribute: - It provides an extended range, ensuring that communities can be assigned for a plethora of uses, without fear of overlap. - The addition of a Type field provides structure for the community space. The addition of structure allows the application of policy based on the application for which the community value will be used. For example, one can filter out all communities of a particular type, or allow only certain values for a particular type of community. Without structure this can only be accomplished by explicitly enumerating all community values which will be denied or allowed. 4. BGP Extended Communities Attribute The Extended Communities Attribute is a transitive optional BGP attribute. The attribute consists of a set of "extended communities". Each extended community is coded as an eight octet value. All routes with the Extended Communities attribute belong to the communities listed in the attribute. The Extended Communities Attribute has Type Code 16. Each Extended Community is encoded as an eight octet quantity, as follows: - Type Field: 2 octets Types 0 through 0x7fff inclusive are assignable by IANA. Types 0x8000 through 0xffff inclusive are vendor-specific. - Value Field: 6 octets When the high-order octet of the Type field is 0x00, the Value field consists of two subfields: Administrator: 2 octets This subfield contains an Autonomous System number assigned by IANA. Assigned Number subfield: 4 octets Ramachandra, Tappan [Page 2] Internet Draftdraft-ramachandra-bgp-ext-communities-04.txt May 2000 This subfield contains a number from a numbering space which is administered by the organization to which the Automous System number in the Administrator subfield has been assigned by IANA. When the high-order octet of the Type field is 0x01, the Value field consists of two subfields: Administrator: 4 octets This subfield contains an IPv4 address assigned by IANA. Assigned Number subfield: 2 octets This subfield contains a number from a numbering space which is administered by the organization to which the IPv4 address in the Administrator subfield has been assigned by IANA. 5. Route Target Community The Route Target Community identifies one or more routers that may receive a set of routes (that carry this Community) carried by BGP. The Type field for the Route Target Community is 0x0002 or 0x0102. 6. Route Origin Community The Route Origin Community identifies one or more routers that inject a set of routes (that carry this Community) into BGP. The Type field for the Route Origin Community is 0x0003 or 0x0103. 7. Link Bandwidth Community When a router receives a route from a directly connected external neigbor (the external neighbor that is one IP hop away), and advertises this route (via IBGP) to internal neighbors, as part of this advertisement the router may carry the bandwidth of the link that connects the router with the external neighbor. This bandwidth is carried in the Link Bandwidth Community, and is encoded as 4 octets in IEEE floating point format. The units are bytes per second. A router is expected to strip the Link Bandwidth Community attribute from a route when advertising this route to an external neighbor. Ramachandra, Tappan [Page 3] Internet Draftdraft-ramachandra-bgp-ext-communities-04.txt May 2000 When a router receives a route with the Link Bandwidth Community, the router should ignore the information carried in the Link Bandwidth Community of the route if this Community was attached to the route by some router that is in a different Autonomous System than the router that receives the route. The router that receives the route determines the Autonomous System of the router that attached the Link Bandwidth Community by examining the Community itself (as it carried the Autonomous System of the router that attached the Community). The Type field for the Link Bandwidth Community is 0x0004. 8. Operations A BGP speaker may use the Extended Communities attribute to control which routing information it accepts, prefers or distributes to its peers. A BGP speaker receiving a route that doesn't have the Extended Communities attribute may append this attribute to the route when propagating it to its peers. A BGP speaker receiving a route with the Extended Communities attribute may modify this attribute according to the local policy. A route may carry both the BGP Communities attribute as defined in [RFC1997]), and the Extended BGP Communities attribute. In this case the BGP Communities attribute is handled as specified in [RFC1997], and the Extended BGP Communities attribute is handled as specified in this document. 9. IANA Considerations As specified in section 4 of this document, an Extended Community Attribute contains a two-byte Type Field. Type Field values 2, 3, and 4 are assigned in this document. Type Field values 5-0x7fff are to be assigned by IANA, using the "First Come First Served" policy defined in RFC 2434. Type values 0x8000-0xffff are for vendor-specific types, and values in this range are not to be assigned by IANA. Ramachandra, Tappan [Page 4] Internet Draftdraft-ramachandra-bgp-ext-communities-04.txt May 2000 10. Security Considerations This extension to BGP does not change the underlying security issues. 11. Acknowledgements To be supplied. 12. References [BGP-4] Rekhter, Y., and T. Li, "A Border Gateway Protocol 4 (BGP- 4)", RFC 1771, March 1995. [RFC1997] Chandra, R., Traina, P., Li, T., "BGP Communities Attribute", RFC1997, August 1996. 13. Author Information Srihari Ramachandra Cisco Systems, Inc. 170 West Tasman Drive San Jose, CA 95134 e-mail: rsrihari@cisco.com Dan Tappan Cisco Systems, Inc. 250 Apollo Drive Chelmsford, MA, 01824 e-mail: tappan@cisco.com Ramachandra, Tappan [Page 5]