The VLAN pruning feature prevents Cisco’s VTP (VLAN Trunking Protocol) from sending VLAN broadcasts (over trunks) to switches within the topology which do not have the particular VLAN configured.
The prerequisite for this feature to work is that all switches within the network topology must:
-Have VTP enabled
-Must be in ‘Server Mode’.
Only if the switches are in ‘Server Mode’ are they able to send VLAN update changes to other switches within the network to inform the addition and deletion of VLANs. These updates then allow the VLAN pruning to take place.