Large BGP Communities

BGP implementations typically support a routing policy language (RPL) to control the distribution of routing information. Network operators add BGP communities to routes via the RPL to identify intrinsic differentia of a route such as its origin country or specify a RPL action to be taken, or one that has been taken, on an individual route or group of routes. Because BGP communities are optional transitive BGP attributes, these differentia and actions identified by the communities may be acted upon or otherwise utilized by the RPL in any Autonomous System (AS) in the Internet, often are and often the goal of adding a community is to signal an AS one or more AS-hops away. BGP Communities Attributes are 4-octet values split into two 2-octet values where the most significant word is an Autonomous System number (ASN) and the least significant word is a value whose meaning is defined by operators of that Autonomous System. This operator-defined value is the aforementioned differentia or RPL action. Since the adoption of Four-octet ASNs , the BGP Communities Attribute can no longer accommodate this encoding because it is only large enough to hold the ASN. Some operators have also expressed a need for more than 2-octets of operator-defined values. This has led operators to create obtuse mappings to fit within 2-octets, the use of which are tedious and error prone and still can not accommodate all use-cases. To address this, a Large Community BGP attribute is defined to encode one or more 12-octet values each consisting of a Four-octet Autonomous System Number and two 4 octet operator-defined values for differentia or actions defined by that Autonomous System.

This document creates the Large Communities BGP path attribute as an optional transitive attribute of variable length. All routes with the Large Community attribute belong to the communities in the attribute. The Large COMMUNITIES attribute has Type Code TBD - RFC EDITOR fill-in IANA assigned value. The attribute consists of one or more 12-octet values. Each 12-octet Large Community value represents three 4-octet values, as follows:

The Four-octet ASN of the operator with whom definition of the final two 4-octet values lies. 4-octet operator-defined value. 4-octet operator-defined value.

The textual representation of BGP Communities in RPLs and the networking community is known well as two 2-octet unsigned integers and is often represented as such, separated a colon. For example, 65000:12345 (ASN:differentia). Large Communities MUST be represented similarly, as three 4-octet unsigned integers with no leading zeros. An integer MUST NOT be omitted, even when zero. Implementations MUST represent Large Communities in RPL in a manner consistent with their representation of BGP Communities . For example, 65000:1:2 (ASN:Local Data Part 1:Local Data Part 2) or 65000:0:0. The following Large BGP Communities textual specification uses the Augmented Backus-Naur Form (ABNF) notation as specified in .

Vendors MAY provide other textual representations.

The error handling of Large Community is as follows: A Large Community BGP Path Attribute with a length of zero MUST be ignored upon receipt and removed when sending. A Large Community attribute SHALL be considered malformed if its length is not a non-zero multiple of 12 bytes. A BGP UPDATE message with a malformed Large Community attribute SHALL be handled using the approach of "treat-as-withdraw" as described in section 2.

This extension to BGP has similar security implications as BGP Communities . underlying security issues. Specifically, an AS relying on the BGP attributes carried in BGP must have trust in every AS in the path to the source of the route, as any AS in the path may have altered or deleted attributes or added false attributes. Specifying the mechanism(s) to provide such trust is beyond the scope of this document.

This section records the status of known implementations of the protocol defined by this specification at the time of posting of this Internet-Draft, and is based on a proposal described in . The description of implementations in this section is intended to assist the IETF in its decision processes in progressing drafts to RFCs. Please note that the listing of any individual implementation here does not imply endorsement by the IETF. Furthermore, no effort has been spent to verify the information presented here that was supplied by IETF contributors. This is not intended as, and must not be construed to be, a catalog of available implementations or their features. Readers are advised to note that other implementations may exist. As of today these vendors have produced an implementation of Large BGP Community: Cisco IOS XR ExaBGP GoBGP The latest implementation news is tracked at http://largebgpcommunities.net/.

IANA is requested to assign a BGP path attribute value for the Large Community attribute.

The authors would like to thank Ruediger Volk, Russ White, Acee Lindem, Shyam Sethuram, Jared Mauch, Joel M. Halpern, Nick Hilliard, Jeffrey Haas, John Heasley, Gunter van de Velde, Marco Marzetti, Eduardo Ascenco Reis, Mark Schouten, Paul Hoogsteder, Martijn Schmidt, Greg Hankins, Acee Lindem, Bertrand Duvivier, Barry O'Donovan, Grzegorz Janoszka, Linda Dunbar, Marco Davids, Gaurab Raj Upadhaya, Jeff Tantsura, Teun Vink, Adam Davenport, Theodore Baschak, Pier Carlo Chiodi, Nabeel Cocker, Ian Dickinson, Jan Baggen, Duncan Lockwood, David Farmer, Randy Bush, Wim Henderickx, Stefan Plug, Kay Rechthien, Rob Shakir, Warren Kumari, Gert Doering, Thomas King, Mikael Abrahamsson, Wesley Steehouwer, Sander Steffann, Brad Dreisbach, Martin Millnert, Christopher Morrow, Jay Borkenhagen, Arnold Nipper, Joe Provo, Niels Bakker, Bill Fenner, Tom Daly, Ben Maddison, Alexander Azimov, Brian Dickson and Peter van Dijk for their support, insightful review and comments.