Forming Bgp Peer Routers - Nortel Alteon OS 42C4911 Application Manual

Alteon OS Application Guide
Typically, an AS has one or more border routers—peer routers that exchange routes with other
ASs—and an internal routing scheme that enables routers in that AS to reach every other router
and destination within that AS. When you advertise routes to border routers on other autono-
mous systems, you are effectively committing to carry data to the IP space represented in the
route being advertised. For example, if you advertise 192.204.4.0/24, you are declaring that if
another router sends you data destined for any address in 192.204.4.0/24, you know how to
carry that data to its destination.

Forming BGP Peer Routers

Two BGP routers become peers or neighbors once you establish a TCP connection between
them. For each new route, if a peer is interested in that route (for example, if a peer would like
to receive your static routes and the new route is static), an update message is sent to that peer
containing the new route. For each route removed from the route table, if the route has already
been sent to a peer, an update message containing the route to withdraw is sent to that peer.
For each Internet host, you must be able to send a packet to that host, and that host has to have a
path back to you. This means that whoever provides Internet connectivity to that host must have
a path to you. Ultimately, this means that they must "hear a route" which covers the section of the
IP space you are using; otherwise, you will not have connectivity to the host in question.
42C4911, January 2007 Chapter 11: Border Gateway Protocol 173