H3C Technologies H3C SecPath F1000-E - Manual (Page 327)

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BGP Configuration
The Border Gateway Protocol (BGP) is a dynamic inter-AS Exterior Gateway Protocol.
When configuring BGP, go to these sections for information you are interested in:
NOTE:
The term router refers to both routers and Layer 3 switches, and BGP refers to BGP-4 in this document.
BGP Overview
Introduction to BGP
There are three early BGP versions, BGP-1 (RFC1105), BGP-2 (RFC1163) and BGP-3 (RFC1267). The
current version in use is BGP-4 (RFC 4271), which is the defacto Internet exterior gateway protocol used
between ISPs.
The characteristics of BGP are as follows:
• Focusing on the control of route propagation and the selection of optimal routes rather than the
route discovery and calculation, which makes BGP, an exterior gateway protocol different from
interior gateway protocols such as OSPF and RIP
• Using TCP to enhance reliability
• Supporting CIDR
• Reducing bandwidth consumption by advertising only incremental updates and therefore
applicable to advertising a great amount of routing information on the Internet
• Eliminating routing loops completely by adding AS path information to BGP routes
• Providing abundant policies to implement flexible route filtering and selection
• Good scalability
A router advertising BGP messages is called a BGP speaker. It establishes peer relationships with other
BGP speakers to exchange routing information. When a BGP speaker receives a new route or a route
better than the current one from another AS, it will advertise the route to all the other BGP peers in the
local AS.
To simplify configuration, multiple peers having an identical policy can be organized as a peer group.
BGP runs on a router in either of the following two modes:
• iBGP (internal BGP)
• eBGP (external BGP)
BGP is called iBGP when it runs within an AS and is called eBGP when it runs between ASs.
Formats of BGP Messages
Header
BGP has five types of messages: