What happens if a switch receives a frame and already has the source MAC address in its MAC table?

When a switch receives a frame and detects that the source MAC address is already present in its MAC address table, it performs a specific action related to managing that entry. The primary function of the switch, in this case, is to refresh the timer associated with the existing MAC address entry.

Switches maintain a MAC address table that maps MAC addresses to the ports on which they were last seen. This table has a timeout mechanism to remove addresses that have not been active for a certain period of time. By refreshing the timer when a frame with a known source MAC address is received, the switch ensures that the address remains in the table even if there are no further communications from that MAC for a while. This helps to maintain an efficient forwarding table and avoids unnecessary flooding of frames within the network.

This process is critical for ensuring optimal performance of the switch, allowing it to efficiently forward frames only to the necessary ports, thus conserving bandwidth and reducing unnecessary traffic.