BGP-4 Protocol Analysis (RFC1774)
Original Publication Date: 1995-Mar-01
Included in the Prior Art Database: 2019-Feb-12
Internet Society Requests For Comment (RFCs)
The purpose of this report is to document how the requirements for advancing a routing protocol to Draft Standard have been satisfied by the Border Gateway Protocol version 4 (BGP-4). This report summarizes the key features of BGP, and analyzes the protocol with respect to scaling and performance. This memo provides information for the Internet community. This memo does not specify an Internet standard of any kind.
Network Working Group P. Traina, Editor Request for Comments: 1774 cisco Systems Category: Informational March 1995
BGP-4 Protocol Analysis
Status of this Memo
This memo provides information for the Internet community. This memo does not specify an Internet standard of any kind. Distribution of this memo is unlimited.
The purpose of this report is to document how the requirements for advancing a routing protocol to Draft Standard have been satisfied by the Border Gateway Protocol version 4 (BGP-4). This report summarizes the key features of BGP, and analyzes the protocol with respect to scaling and performance. This is the first of two reports on the BGP protocol.
BGP-4 is an inter-autonomous system routing protocol designed for TCP/IP internets. Version 1 of the BGP protocol was published in RFC 1105. Since then BGP versions 2, 3, and 4 have been developed. Version 2 was documented in RFC 1163. Version 3 is documented in RFC1267. The changes between versions are explained in Appendix 2 of .
Possible applications of BGP in the Internet are documented in .
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Key features and algorithms of the BGP-4 protocol.
This section summarizes the key features and algorithms of the BGP protocol. BGP is an inter-autonomous system routing protocol; it is designed to be used between multiple autonomous systems. BGP assumes that routing within an autonomous system is done by an intra- autonomous system routing protocol. BGP does not make any assumptions about intra-autonomous system routing protocols employed by the various autonomous systems. Specifically, BGP does not require all autonomous systems to run the same intra-autonomous system routing protocol.
BGP is a real inter-autonomous system routing protocol. It imposes no constraints on the underlying Internet topology. The information exchanged via BGP is sufficient to construct a graph of autonomous systems connectivity from which routing loops may be pruned and some
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RFC 1774 BGP-4 Protocol Analysis March 1995
routing policy decisions at the autonomous system level may be enforced.
The key features of the protocol are the notion of path attributes and aggregation of network layer reachability information (NLRI).
Path attributes provide BGP with flexibility and expandability. Path attributes are partitioned into well-known and optional. The provision for optional attributes allows experimentation that may involve a group of BGP routers without affecting the rest of the Internet. New optional attributes can be added to the protocol in much the same fashion as new options are added to the Telnet protocol, for instance.
One of the most important path attributes is the AS-PATH. AS reachability information traverses the Internet, this information is augmented by the list of autonomous systems that have been traversed thus far, forming the AS-PATH. The AS-PATH allows straightforward suppression of the looping of routing information. In addit...