Blade ICE G8124 Manuale Utente

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  Chapter 5: Access Control Lists

BMD00220, October 2010

The G8124 provides filters that can limit the number of the following packet types transmitted by 
switch ports: 

Broadcast packets

Multicast packets

Unknown unicast packets (destination lookup failure)

Excessive transmission of broadcast or multicast traffic can result in a broadcast storm. A broadcast 
storm can overwhelm your network with constant broadcast or multicast traffic, and degrade 
network performance. Common symptoms of a broadcast storm are slow network response times 
and network operations timing out. 

Unicast packets whose destination MAC address is not in the Forwarding Database are 
unknown unicasts. When an unknown unicast is encountered, the switch handles it like a broadcast 
packet and floods it to all other ports in the VLAN (broadcast domain). A high rate of unknown 
unicast traffic can have the same negative effects as a broadcast storm. 

Configure broadcast filters on each port that requires broadcast storm control. Set a threshold that 
defines the total number of broadcast packets transmitted (100-10000), in Megabits per second. 
When the threshold is reached, no more packets of the specified type are transmitted.

Up to nine storm filters can be configured on the G8124.

To filter broadcast packets on a port, use the following commands: 

To filter multicast packets on a port, use the following commands: 

To filter unknown unicast packets on a port, use the following commands: 

RS G8124(config)# interface port 1

RS G8124(config-if)# broadcast-threshold

RS G8124(config-if)# multicast-threshold

RS G8124(config-if)# dest-lookup-threshold

RS G8124(config-if)# exit