Preventing The Forwarding Of Dynamically Learned Stations - Cisco Catalyst 3550 series Software Configuration Manual

Chapter 36 Configuring Fallback Bridging
This example shows how to create bridge group 10, to specify that the VLAN-bridge STP runs in the
bridge group, to define an interface as a routed port, and to assign the interface to the bridge group:
Switch(config)# bridge 10 protocol vlan-bridge
Switch(config)# interface gigabitethernet0/1
Switch(config-if)# no switchport
Switch(config-if)# no shutdown
Switch(config-if)# bridge-group 10
This example shows how to create bridge group 10 and to specify that the VLAN-bridge STP runs in the
bridge group. It defines an interface as an SVI and assigns this interface to VLAN 2 and to the bridge
group:
Switch(config)# bridge 10 protocol vlan-bridge
Switch(config)# vlan 2
Switch(config-vlan)# exit
Switch(config)# interface vlan2
Switch(config-if)# exit
Switch(config)# interface gigabitethernet0/2
Switch(config-if)# switchport mode access
Switch(config-if)# switchport access vlan 2
Switch(config-if)# no switchport
Switch(config-if)# no shutdown
Switch(config-if)# bridge-group 10

Preventing the Forwarding of Dynamically Learned Stations

By default, the switch forwards any frames for stations that it has dynamically learned. By disabling this
activity, the switch only forwards frames whose addresses have been statically configured into the
forwarding cache.
Beginning in privileged EXEC mode, follow these steps to prevent the switch from forwarding frames
for stations that it has dynamically learned:
Command
Step 1
configure terminal
Step 2
no bridge bridge-group acquire
Step 3 end
Step 4
show running-config
Step 5 copy running-config startup-config
To cause the switch to forward frames to stations that it has dynamically learned, use the bridge
bridge-group acquire global configuration command.
78-11194-09
Purpose
Enter global configuration mode.
Enable the switch to stop forwarding any frames for stations that it has
dynamically learned through the discovery process and to limit frame
forwarding to statically configured stations.
The switch filters all frames except those whose destined-to addresses
have been statically configured into the forwarding cache. To configure
a static address, use the bridge bridge-group address mac-address
{forward | discard} global configuration command.
For bridge-group, specify the bridge group number. The range is 1
to 255.
Return to privileged EXEC mode.
Verify your entry.
(Optional) Save your entry in the configuration file.
Catalyst 3550 Multilayer Switch Software Configuration Guide
Configuring Fallback Bridging
36-5