BGP Communities Attribute (RFC1997)
Original Publication Date: 1996-Aug-01
Included in the Prior Art Database: 2019-Feb-14
Internet Society Requests For Comment (RFCs)
R. Chandra: AUTHOR [+2]
This document describes an extension to BGP which may be used to pass additional information to both neighboring and remote BGP peers. [STANDARDS-TRACK]
Network Working Group R. Chandra Request for Comments: 1997 P. Traina Category: Standards Track cisco Systems T. Li August 1996
BGP Communities Attribute
Status of This Memo
This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited.
Border Gateway Protocol  is an inter-autonomous system routing protocol designed for TCP/IP internets.
This document describes an extension to BGP which may be used to pass additional information to both neighboring and remote BGP peers.
The intention of the proposed technique is to aid in policy administration and reduce the management complexity of maintaining the Internet.
BGP supports transit policies via controlled distribution of routing information. Mechanisms for this are described in  and have been successfully used by transit service providers. However, control over the distribution of routing information is presently based on either IP address prefixes or on the value of the AS_PATH attribute (or part of it).
To facilitate and simplify the control of routing information this document suggests a grouping of destinations so that the routing decision can also be based on the identity of a group. Such a scheme is expected to significantly simplify a BGP speaker’s configuration that controls distribution of routing information.
Chandra, et. al. Standards Track [Page 1]
RFC 1997 BGP Communities Attribute August 1996
Terms and Definitions
Community A community is a group of destinations which share some common property.
Each autonomous system administrator may define which communities a destination belongs to. By default, all destinations belong to the general Internet community.
A property such as "NSFNET sponsored/AUP" could be added to all AUP compliant destinations advertised into the NSFNET. NSFNET operators could define a policy that would advertise all routes, tagged or not, to directly connected AUP compliant customers and only tagged routes to commercial or external sites. This would insure that at least one side of a given connection is AUP compliant as a way of enforcing NSF transit policy guidelines.
In this example, we have just eliminated the primary motivation for a complex policy routing database that is used to generate huge prefix and AS path based filter rules. We have also eliminated the delays caused by the out-of-band maintenance of this database (mailing in NACRs, weekly configuration runs, etc.)
A second example comes from experience with aggregation. It is often useful to advertise both an aggregate prefix and the component more- specific prefixes that were used to form the aggregate to optimize "next hop" routing. These component prefixes are only useful to the neighboring BGP...