The Storm-Constrain function is used to avoid the packet-storm on a port. Three types of flux can be set observed respectively: broadcast, multicast and unicast. If an observed flux exceeds its upper limit, this kind of flux will be recognized as over-upper-flux. This kind of flux will be considered as normal-flux until it falls below its lower limit. If any type of observed flux is over-upper-flux, the port will change its status to controlled-status, that is to stop packet forwarding to avoid storm. Only when all the observed fluxes are not over-upper-flux, will the port return to normal(forwarding) status.