13.1.1 Overview

BGP4 is a routing protocol used for Internet connections over which vast amounts of routing information need to be exchanged between Internet service providers (ISPs). BGP4 is based on hierarchical network concepts, and is used for the exchange of routing tables between ISPs at the Internet backbone level. It is also used for connecting an intranet to two or more ISPs.

Within an AS, routing information is exchanged using an Interior Gateway Protocol (IGP) such as RIP or OSPF. BGP4 is an Exterior Gateway Protocol (EGP) that operates between ASs. It can handle all the routing information used on the Internet.

The following table summarizes BGP4 functionality.

Table 13-1 Function of BGP4(IPv4)

Functionality	BGP4
EBGP, IBGP peering, and route distribution	OK
Route filtering and BGP attribute manipulation	OK
Community	OK
Route reflection	OK
Confederations	OK
Capability negotiation	OK
Route refresh capability	OK
Multipath	OK
Peer group*1	OK
Route flap dampening*2	OK
BGP4 MIB #2	OK
TCP MD5 authentication	OK
Graceful restart	OK
Maximum number of learned routes	OK