Established state

Established state Once a BGP speaker reaches the Established state, all of the neighbor negotiations
are complete. As long as everything goes right, the BGP peers exchange UPDATE messages and
KEEPALIVE messages. Each time a BGP speaker receives an UPDATE message or KEEPALIVE
252 Chapter 8  Border Gateway Protocol
message, it resets its hold timer. If the hold timer ever expires before an UPDATE message or KEEPALIVE
message is received, the BGP speaker sends a NOTIFICATION message to its peer, terminates
the TCP session, and changes its state to Idle. The other events that will cause a BGP speaker
to change its state to Idle are if it receives a NOTIFICATION message from its peer, an error is
detected in the UPDATE message, a disconnect message is received from TCP, a stop event is initiated,
or any other event occurs that causes the BGP speaker to generate a NOTIFICATION message.
All BGP start events are ignored in the Established state.
Once BGP peers have reached the Established state, they will start exchanging routing information.
Now would be a good time for us to take a look at how a BGP speaker copes with the
exchange of routing information.