A read-write enumeration selecting the action taken on a port when a loopback is detected: warnTrap(1) just sends a notification, block(2) blocks the port's traffic, learning(3) keeps learning but takes some other action, or shutdown(4) disables the port entirely. This lets an admin tune how aggressively the switch responds to a detected physical loop, trading off automatic protection against the risk of unexpectedly taking a port out of service. An admin wanting visibility without disruption might set this to warnTrap(1), while one prioritizing network protection against broadcast storms would choose shutdown(4).