694 Configuring Port-Based Traffic ControlWhat is Storm Control?A LAN storm is the result of an excessive number of broadcast, multicast, orunknown unicast messages simultaneously transmitted across a network by asingle port. Forwarded message responses can overload network resources andcause network congestion.The storm control feature allows the switch to measure the incomingbroadcast, multicast, and/or unknown unicast packet rate per port and discardpackets when the rate exceeds the defined threshold. Storm control is enabledper interface, by defining the packet type and the rate at which the packetsare transmitted. For each type of traffic (broadcast, multicast, or unknownunicast) you can configure a threshold level, which is expressed as apercentage of the total available bandwidth on the port. If the ingress rate ofthat type of packet is greater than the configured threshold level the portdrops the excess traffic until the ingress rate for the packet type falls belowthe threshold.The actual rate of ingress traffic required to activate storm-control is based onthe size of incoming packets and the hard-coded average packet size of 512bytes - used to calculate a packet-per-second (pps) rate - as the forwarding-plane requires PPS versus an absolute rate Kbps. For example, if theconfigured limit is 10%, this is converted to ~25000 PPS, and this PPS limitis set in the hardware. You get the approximate desired output when 512 bytespackets are used.What are Protected Ports?The switch supports up to three separate groups of protected ports. Trafficcan flow between protected ports belonging to different groups, but notwithin the same group.A port can belong to only one protected port group. You must remove aninterface from one group before adding it to another group.Port protection occurs within a single switch. Protected port configurationdoes not affect traffic between ports on two different switches. No trafficforwarding is possible between two protected ports.
