Broadcast Storm Control | 104351Broadcast Storm ControlBroadcast Storm Control is supported on platforms: c e sThis chapter contains the following configuration topics:• Layer 3 Broadcast Storm Control on page 1044• Layer 2 Broadcast Storm Control on page 1045• Multicast Storm Control on page 1046Storm Control OverviewFTOS Storm Control is a preventative measure against unexpectedly high rates of broadcast or multicastpackets; these traffic bursts are called storms. If the rate of these packets on ingress or egress exceeds auser-defined threshold, FTOS, when configured, can suppress forwarding for these packets until the packetrate falls back to the configured limit.Situations that Can Lead to Packet Storms• Layer 2 Broadcasts—A switch might not have an entry in its MAC address table that matches apacket’s destination MAC. In this case, the switch floods the packet on the VLAN. These packets arecalled unknown-packets; they cause unnecessary extra traffic and can reduce network performance.• Layer 3 Broadcast Packets—There are two types of Layer 3 broadcast packets: the all-hostsbroadcast, the IP address of which is 255.255.255.255, and the subnet broadcast address, the address ofwhich has the host portion of the address set to all ones; for example, 10.11.1.255/24 is the broadcastaddress for the 10.11.1.0 network. Some protocols utilize broadcasts more than others and so stormcontrol might be useful to prevent congestion.• Multicast Packets—Multicast packets are packets that use a special range of MAC and IP addressesto send packets to a group of hosts, rather than a single host. Some multicast applications can causeexcessive bandwidth consumption, and storm control can be used (in conjunction with IGMPSnooping) to limit multicast traffic.
