BGP MESSAGE TYPES
• Open: After a neighbor is configured, BGP sends an open message to try to establish peering. The message includes AS, Router ID, and hold time.
• Update: Message used to transfer routing information between peers. Includes new routes, withdrawn routes, and path attributes.
• Keepalive: BGP peers echange keepalives every 60 seconds by default. These are used to maintain the peering session active.
• Notification: When a problem occurs that causes a router to end BGP peering, a notification message is sent to the neighbor, and the connection is closed.