Manual VLAN Pruning

VTP can prune VLANs but only for VLANs 2-1001, this includes VTP version 3 which supports extended-range VLANs. So really the best way to prune VLANs is manually.

Pruning VLANs helps reduces broadcast traffic by preventing and sending unnecessary broadcast, multicast and unicast traffic. (Think unknown unicast flooding). It also can help enhance security by limiting the expose or spread of VLAN traffic from potential attacks and unauthorized access. Pruning can also just optimize bandwidth by ensuring that trunk links only carry the VLANs they need.

Just like if you were gardening, pruning helps remove those unnecessary branches to keep your network/plants in a healthy state.🌱

Pruning VLANs

Remember by default switchport mode trunk allows all VLANs on a trunk interface, pruning VLANs is to use the switchport trunk allowed vlan or switchport trunk remove vlan on a trunk interface. This allows or removes certain VLANs on that trunk interface.

If you are managing a network only you would know what VLANs are and are not needed by looking downstream. If a VLAN is not used downstream in an access or another trunk port then it’s likely safe to prune it from the trunk.