Unicast flood

The process occurs when a device is initially connected to a network segment, or after its address and port identifier is purged from the forwarding information base.

An entry is purged when the link goes down on the original port or when it expires due to inactivity (five minutes is the default on many switches).

Another common cause is a host with an ARP cache timeout longer than the timeout of the forwarding information base (FIB) in a switch—the switch forgets which port connects to the target before the host forgets the MAC address of the target.

After ensuring that timeouts and security features have been configured to maintain table entries on client access ports longer than typical host ARP cache timeouts, this command is used to quiet down the unicast floods on those ports:[5][6] Other techniques involve isolating hosts at Layer 2.

In high-volume networks, the flooded traffic may cause ports to saturate, leading to packet loss and high latency.