BGP Overview

Border gateway protocol (BGP) is an exterior routing protocol that was developed for use in TCP/IP networks. The primary function of BGP is to allow different autonomous systems (ASs) to exchange network reachability information.

An AS is a set of routers that are under a single technical administration. This set of routers uses a different routing protocol, for example Open Shortest Path First (OSPF), for intra-AS routing. One or more routers in the AS are configured to be border routers, exchanging information with other border routers (in different ASs) on behalf of all of the intra-routers.

BGP can be used as an exterior border gateway protocol (referred to as EBGP), or it can be used within an AS as an interior border gateway protocol (referred to as IBGP).

For more information on BGP, refer to the following documents:
  • RFC 1745—BGP/IDRP for IP—OSPF Interaction
  • RFC 1771—Border Gateway Protocol version 4 (BGP-4)
  • RFC 1965—Autonomous System Confederations for BGP
  • RFC 1966—BGP Route Reflection
  • RFC 1997—BGP Communities Attribute
  • RFC 2385—Protection of BGP Sessions via the TCP RSA Data Security, Inc. MD5 Message-Digest Algorithm Signature Option
  • RFC 2439—BGP Route Flap Damping
  • RFC 2545—Use of BGP-4 Multiprotocol Extensions for IPv6 Inter-Domain Routing
  • RFC 2796—BGP Route Reflection - An Alternative to Full Mesh IBGP
  • RFC 2918—Route Refresh Capability for BGP-4
  • RFC 3392—Capabilities Advertisement with BGP-4
  • RFC 4271—Border Gateway Protocol 4 (BGP-4)
  • RFC 4360—BGP Extended Communities Attribute
  • RFC 4456—BGP Route Reflection: An Alternative to Full Mesh Internal BGP (IBGP)
  • RFC 4486—Subcodes for BGP Cease Notification Message
  • RFC 4724—Graceful Restart Mechanism for BGP
  • RFC 4760—Multiprotocol Extensions for BGP-4
  • RFC 4893—BGP Support for Four-octet AS Number Space
  • RFC 5396—Textual Representation of Autonomous System (AS) Numbers
  • draft_ieft_idr_restart_10.txt—Graceful Restart Mechanism for BGP


ExtremeXOS supports BGP version 4 only, and does not support connections to peers running older versions of BGP.

For complete information about software licensing, including how to obtain and upgrade your license and what licenses are appropriate for these features, see the Feature License Requirements document..