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CLI-based Configuration Guide - IP Unicast Routing

AR100, AR120, AR150, AR160, AR200, AR1200, AR2200, AR3200, and AR3600 V200R009

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Overview of BGP

Overview of BGP


The Border Gateway Protocol (BGP) is a distance vector protocol that allows devices between Autonomous Systems (ASs) to communicate and selects optimal routes. BGP-1, BGP-2, and BGP-3 are three earlier versions of BGP. BGP-4 has been used since 1994. Since 2006, unicast IPv4 networks have been using BGP-4, and other networks (such as IPv6 networks) have been using MP-BGP.

MP-BGP is an extension of BGP-4 and applies to different networks; however, the original message exchange and routing mechanisms of BGP-4 are not changed. MP-BGP applications on IPv6 unicast and IPv4 multicast networks are called BGP4+ and Multicast BGP (MBGP) respectively.


A network is divided into different ASs to facilitate the management over the network. In 1982, the Exterior Gateway Protocol (EGP) was used to dynamically exchange routing information between ASs. EGP advertises only reachable routes but not select optimal routes or prevent routing loops. Therefore, EGP cannot meet network management requirements.

BGP was designed to replace EGP. Different from EGP, BGP can select optimal routes, prevent routing loops, transmit routing information efficiently, and maintain a large number of routes.

Although BGP is used to transmit routing information between ASs, BGP is not the best choice in some scenarios. For example, on the egress connecting a data center to the Internet, static routing instead of BGP is used to prevent a huge number of Internet routes from affecting the internal network of the data center.


BGP ensures high network security, flexibility, stability, reliability, and efficiency:
Updated: 2019-12-27

Document ID: EDOC1000174069

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