Introduction
BGPv4 (RFC 4271) is the defacto internet exterior gateway protocol used between ISPs.
The characteristics of BGP are:
• Controls route propagation and the selection of optimal routes, rather than route discovery and calculation,
which makes BGP different from interior gateway protocols such as OSPF and RIP.
• Uses TCP to enhance reliability.
• Supports CIDR.
• Reduces bandwidth consumption by advertising only incremental updates, which allows advertising large
amounts of routing information on the Internet.
• Eliminates routing loops completely by adding AS path information to BGP routes.
• Provides policies to implement flexible route filtering and selection.
• Provides scalability.
A router that advertises BGP messages is called a BGP speaker. The BGP speaker 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 advertises the route to all the other BGP peers in
the local AS.
BGP can be configured to run on a router in the following two modes:
• iBGP (internal BGP)
• eBGP (external BGP)
When a BGP speaker peers with another BGP speaker that resides in the same autonomous system, the session
is referred to as an iBGP session. When a BGP speaker peers with a BGP speaker that resides in a different
autonomous system, the session is referred to as an eBGP session.
Chapter 17
Border Gateway Protocol (BGP)
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Aruba 3810 / 5400R Multicast and Routing Guide for ArubaOS-
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