1. Open message: This is the first message exchanged between two BGP peers, during the session setup process. It contains information such as the BGP version number, router ID, and autonomous system (AS) number.
1. Update message: This is the most important BGP message, as it carries routing updates and changes for the prefixes exchanged between BGP peers.
1. Keepalive message: This message is primarily used to keep the BGP session active, once it has been established. It is sent periodically between BGP peers to indicate that they are still connected.
1. Notification message: This message is sent by a BGP peer to notify the other peer of an error condition or an issue with the BGP session. It can be generated by either the local or remote BGP peer.
1. Route Refresh message: This message is used to request an update of all the routes from a particular BGP peer. It is commonly used when the BGP table has been modified, and a full update is needed.
