The TCP Keepalive Timer feature provides a mechanism to identify dead connections.
When a TCP connection on a routing device is idle for too long, the device sends a TCP keepalive packet to the peer with
only the Acknowledgment (ACK) flag turned on. If a response packet (a TCP ACK packet) is not received after the device sends
a specific number of probes, the connection is considered dead and the device initiating the probes frees resources used by
the TCP connection.
The following parameters are used to configure TCP keepalive:
TCP Keepalive idle time—The value of this parameter indicates the time for which a TCP connection can be idle before the
connection initiates keepalive probes.
TCP Keepalive retries—The value of this parameter is the number of unacknowledged probes that a device can send before declaring
the connection as dead and tearing it down.
TCP Keepalive interval—The time between subsequent probe retries.