What happens in Protect mode of port security?

In Protect mode of port security, the behavior of the switch regarding packets with unknown source MAC addresses is crucial to understanding its operation. When the switch encounters a packet with an unknown source MAC address, it does not allow that packet through. Instead, the switch drops these packets, effectively blocking devices that are not recognized according to the established MAC address table.

This process continues until the switch reaches a predefined security count, which is the configured limit of unknown MAC addresses that can be handled. Once this limit is reached, the action taken by the switch may escalate depending on the configuration, possibly leading to the enforcement of additional security measures.

Protect mode does not stop all traffic entirely, nor does it allow unknown packets to be sent through. It's also not a monitoring-only mode, as it actively prevents unauthorized access based on MAC address recognition. By utilizing Protect mode, network administrators can maintain a degree of security without completely halting all communication, which would severely impact network functionality.