How VTP Pruning works

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VTP pruning function use by reducing unnecessary flooded traffic, such as broadcast, multicast, unknown, and flooded unicast packets. VTP pruning save and increases available bandwidth by restricting flooded traffic to those trunk links that the traffic must use to access the appropriate network devices. By default, VTP pruning is disabled. VTP pruning does not prune traffic from VLANs that are pruning-ineligible.

What VTP Pruning does,

   

• VLAN 1(default) is always pruning-ineligible, meaning traffic from VLAN 1 cannot be pruned in any situation.
  
• Pruning eligibility is based only on the VLANs that need the given broadcast information across the trunks. It is not related with the number of ports assigned to that VLAN.
• VTP Pruning does not change, add, or delete the VLANs in a VTP domain, it simply reduces the broadcast and multicast traffic.
• VTP version 2 and VTP version 1 are not interoperable on network devices in the same
  VTP domain. Every network device in the VTP domain must use the same VTP version.
  Do not enable VTP version 2 unless every network device in the VTP domain supports
  version 2.   

 

 Reference:http://www.cisco.com/univercd/cc/td/doc/product/lan/cat5000/rel_4_2/config/vlans.htm#xtocid79802