BGP Message Types
BGP has four types of messages:
�¡ Open.After a neighbor is configured, BGP sends an open message to
try to establish peering with that neighbor. Includes information such
as autonomous system number, router ID, and hold time.
�¡ Update.Message used to transfer routing information between peers.
�¡ Keepalive.BGP peers exchange keepalive messages every 60
seconds by default. These keep the peering session active.
�¡ Notification.When a problem occurs that causes a router to end the
BGP peering session, a notification message is sent to the BGP neighbor
and the connection is closed.