keepalive — interface
The keepalive interval
keepalive command specifies the interval (in
seconds) that the router waits before sending a message on the interface to test the link and determine whether it is up or down. On Ethernet interfaces, the router sends the message to itself. On serial interfaces, the message is sent to the router on the other end of the link.
Keepalive settings can be very sensitive. If the keepalive interval is too low, the keepalive packets might be delayed by other traffic. If the interval is set too high, the router will take longer to update the interface’s status, which slows route convergence.
On Frame Relay interfaces, the keepalive value should match (or be less than) the LMI interval configured on the carrier’s switch.
interface ethernet 1 keepalive 5