The following example configures Tunnel 1 to send keepalive packets every 20 seconds. If the tunnel’s destination interface fails to respond to three consecutive packets, the tunnel’s source interface concludes that the tunnel is down. The source interface continues to send keepalive packets, but until it receives a response from the tunnel’s destination interface, the tunnel informs hosts that send packets to the tunnel that the tunnel is down.

Gxxx-001# interface tunnel 1
Gxxx-001(if:Tunnel 1)# keepalive 20 3
Done!