Cisco WS-C2960S-48TD-L Software Guide - Page 202

Configuring Flooding Controls Chapter 7 Configuring the Switch Ports Configuring Flooding Controls You can use these flooding techniques to block the forwarding of unnecessary flooded traffic: • Enable storm control for unicast, multicast, or broadcast packets • Block the forwarding of unicast and broadcast packets on a per-port basis • Flood all unknown packets to a network port (configured only by using CLI) Note The switch supports the store-and-forward switching mode. Store-and-forward mode stores complete packets and checks for errors before transmission. It is the most error-free form of switching. Enabling Storm Control A packet storm occurs when a large number of broadcast, unicast, or multicast packets are received on a port. Forwarding these packets can cause the network to slow down or to time out. Storm control is configured for the switch as a whole but operates on a per-port basis. By default, storm control is disabled. Storm control uses high and low thresholds to block and then restore the forwarding of broadcast, unicast, or multicast packets. You can also set the switch to shut down the port when the rising threshold is reached. The rising threshold is the number of packets that a switch port can receive before forwarding is blocked. The falling threshold is the number of packets below which the switch resumes normal forwarding. In general, the higher the threshold, the less effective the protection against broadcast storms. The maximum half-duplex transmission on a 100BASE-T link is 148,000 packets per second, but you can enter a threshold of up to 4294967295 broadcast packets per second. Beginning in privileged EXEC mode, follow these steps to enable broadcast-storm control. (To enable storm control on multicast packets, use the port storm-control multicast command. To enable storm control on unicast packets, use the port storm-control unicast command.) Step 1 Step 2 Step 3 Step 4 Step 5 Step 6 Command Purpose configure terminal Enter global configuration mode. interface interface Enter interface configuration mode, and enter the port to configure. port storm-control broadcast [threshold {rising rising-number falling falling-number}] Enter the rising and falling thresholds for broadcast packets. Make sure the rising threshold is greater than the falling threshold. port storm-control trap Generate an SNMP trap when the traffic on the port crosses the rising or falling threshold. end Return to privileged EXEC mode. show port storm-control [interface] Verify your entries. Catalyst 2900 Series XL and Catalyst 3500 Series XL Software Configuration Guide 7-4 78-6511-08