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Table Of Contents  The TCP/IP Guide
 9  TCP/IP Lower-Layer (Interface, Internet and Transport) Protocols (OSI Layers 2, 3 and 4)
      9  TCP/IP Internet Layer (OSI Network Layer) Protocols
           9  TCP/IP Routing Protocols (Gateway Protocols)
                9  TCP/IP Exterior Gateway/Routing Protocols (BGP and EGP)
                     9  TCP/IP Border Gateway Protocol (BGP/BGP-4)
                          9  BGP Fundamentals and General Operation

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BGP Fundamentals and General Operation
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BGP Topology, Speakers, Border Routers and Neighbor Relationships (Internal and External Peers)
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BGP Overview, History, Standards and Versions
(Page 2 of 4)

BGP Evolution, Versions and Defining Standards

Due to the importance of a protocol that spans the Internet, work continued on BGP for many years after the initial standard was published. The developers of BGP had to correct problems with the initial protocol, refine BGP's operation, improve efficiency, and add features. It was also necessary to make adjustments to allow BGP to keep pace with other changes in the TCP/IP protocol suite, such as the invention of classless addressing and routing.

The result of this ongoing work is that BGP has evolved through several versions and standards. These are sometimes called BGP-N where N is the version number. Table 133 shows the history of BGP standards, providing the RFC numbers and names and a brief summary of the changes made in each version.

Table 133: Border Gateway Protocol (BGP) Versions and Defining Standards

RFC Number



BGP Version



June 1989

A Border Gateway Protocol (BGP)


Initial definition of the BGP protocol.


June 1990

A Border Gateway Protocol (BGP)


This version cleaned up several issues with BGP-1, and refined the meaning and use of several of the message types. It also added the important concept of path attributes, which communicate information about routes.

BGP-1 was designed around the notion of a directional topology, with certain routers being “up”, “down” or “horizontal” relative to each other; BGP-2 removed this concept, making BGP better suited to an arbitrary AS topology.

Note that the RFC title is not a typo; they didn't put “version 2” in the title.


October 1991

Border Gateway Protocol 3 (BGP-3)


This version optimized and simplified route information exchange, adding an identification capability to the messages used to establish BGP communications, and incorporating several other improvements and corrections.

(They left the “A” off the title of this one for some reason.


July 1994

A Border Gateway Protocol 4 (BGP-4)


Initial standard for BGP-4, revised in RFC 1771. See just below.


March 1995

A Border Gateway Protocol 4 (BGP-4)


Current standard for BGP-4. The primary change in BGP-4 is support for Classless Inter-Domain Routing (CIDR). The protocol was changed to allow prefixes to be specified that represent a set of aggregated networks. Other minor improvements were also made to the protocol.

As you might imagine, changing the version of a protocol like BGP is not an easy undertaking. Any modification of the protocol would require the coordination of many different organizations. The larger the Internet grows, the more difficult this would be. As a result, despite frequent version changes in the early 1990s, BGP-4 remains today the current version of the standard, and is the one that is widely used. Unless otherwise specified, any mention of BGP in this Guide refers to BGP-4.

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