A port security feature which controls the address learning capability and traffic forwarding decisions. Each port can be enabled or disabled for this function. When it is enabled and a number is given said N, which allows N addresses to be learned on this port, the first N learned addresses are locked at this port as static entries. When the learned addresses number reaches N, any incoming packet without learned source addresses are discarded (e.g. dropped) and no more new addresses can be learned on this port.