What message type does Border Gateway Protocol (BGP) send to test the state of a connection?

BGP uses the KeepAlive message type to verify and maintain the connection state between BGP peers. This kind of message is critical for ensuring that the BGP session remains active. KeepAlive messages are sent periodically to indicate to the other peer that the session is still valid and to prevent the session from timing out due to inactivity.

When two BGP routers form a connection, they begin with an Open message to establish the session. After this initial setup, KeepAlive messages are exchanged to confirm that both peers are still reachable and operational. If a router does not receive a KeepAlive message within a certain timeframe, it may assume that the connection has failed and will take steps to terminate the session and potentially re-establish it.

This functionality is essential for the stability and reliability of BGP routing in complex networks, making it a foundational component of the communication protocol.