Monday, October 20, 2008

VTP and Pruning

I came across the following lab requirement that initially had me puzzled.

SW1 and SW2 are part of the same VTP domain and VTP pruning is enabled - SW1 is in server mode and SW2 is in client mode. SW1 and SW2 are connected via a trunk interface. SW1 has vlan 10 and ports active in this vlan. SW2 has no ports in vlan 10. Ensure SW2 continues to receive unknown unicast, broadcast and multicast traffic for vlan 10 over the trunk link?

Of course with pruning enabled the default behaviour is for vlan 10 traffic to be pruned from the trunk interface. This is the required function of pruning!

VTP pruning is a global command and so changing this is not an option. In fact the solution to this problem is to make use of the 'switchport trunk pruning' interface command. This command takes precedence over the global setting.

Hence to achieve the lab requirement i entered the following command under the trunk interface.

config-if#switchport trunk pruning 2-9,11-1001

To examine the port pruning status use the 'show interface x switchport' command.

SW2#s int fa0/13 switchport | inc Pruning
Pruning VLANs Enabled: 2-9,11-1001

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