Autonomous System Confederations for BGP (RFC1965)
Original Publication Date: 1996-Jun-01
Included in the Prior Art Database: 2019-Feb-12
Internet Society Requests For Comment (RFCs)
This document describes an extension to BGP which may be used to create a confederation of autonomous systems which is represented as one single autonomous system to BGP peers external to the confederation. This memo defines an Experimental Protocol for the Internet community.
Network Working Group P. Traina Request for Comments: 1965 cisco Systems Category: Experimental June 1996
Autonomous System Confederations for BGP
Status of this Memo
This memo defines an Experimental Protocol for the Internet community. This memo does not specify an Internet standard of any kind. Discussion and suggestions for improvement are requested. Distribution of this memo is unlimited.
Border Gateway Protocol  is an inter-autonomous system routing protocol designed for TCP/IP networks.
This document describes an extension to BGP which may be used to create a confederation of autonomous systems which is represented as one single autonomous system to BGP peers external to the confederation.
The intention of this extension is to aid in policy administration and reduce the management complexity of maintaining a large autonomous system.
The extension this document describes is widely deployed in the Internet today.
It may be useful to subdivide autonomous systems with a very large number of BGP speakers into smaller domains for purposes of controlling routing policy via information contained in the BGP AS_PATH attribute. For example, one may chose to consider all BGP speakers in a geographic region as a single entity.
In addition to improvements in routing policy control, current techniques for deploying BGP among speakers in the same autonomous system establish a full mesh of TCP connections among all speakers for the purpose of exchanging exterior routing information. In autonomous systems the number of intra-domain connections that need to be maintained by each border router can become significant.
Subdividing a large autonomous system allows a significant reduction in the total number of intra-domain BGP connections, as the
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RFC 1965 AS Confederations for BGP June 1996
connectivity requirements simplify to the model used for inter-domain connections.
Unfortunately subdividing an autonomous system may increase the complexity of policy routing based on AS_PATH information for all members of the Internet. Additionally, this division increases the maintenance overhead of coordinating external peering when the internal topology of this collection of autonomous systems is modified.
Finally, dividing a large AS may unnecessarily increase the length of the sequence portions of the AS_PATH attribute. Several common BGP implementations can use the number of "hops" required to reach a given destination as part of the path selection criteria. While this is not an optimal method of determining route preference, given the lack of other in-band information, it provides a reasonable default behavior which is widely used across the Internet. Therefore, division of an autonomous system into separate systems may adversely affect optimal routing of packets through the Internet.
However, there is usually no need to expose the internal topology of this divided autonomous system, which means it is possible...