When a secure port receives a frame, the source MAC address of the frame is compared to the list of secure MAC addresses associated with the port. These secure MAC addresses are either manually configured or auto-configured or learned on the port. If the source MAC address of a frame differs from the list of secure addresses, the port either shuts down or the port drops incoming frames from unauthorized host. The default behavior of a secure port is to shut down until it is administratively enabled. The behavior of the port depends on how you configure it to respond to a security violation.