VLAN Trunking Protocol (VTP)

 

VTP Part 1

Pruning:

Pruning eligible list :- VLANs that are assigned in the pruning eligible list are "eligible" to be pruned. i.e. you're saying, prune (or remove) VLANs that NOT requested by other switches when trunked.
When you remove a VLAN from the "prune eligible" list, you're saying that VLAN(s) should not be pruned. i.e. the VLAN(s) are to be present on the trunk all the time.

Configuration:
You configure this on the trunk ports on a L2/3 switch;
SW1(config)#int range g1/0/13 - 21
SW1(config-if-range)#switchport trunk pruning vlan 2-6,8-1001
The second line adds VLANs 2-1001 in the prune eligible list except VLAN 7.

Verification
SW1#sh int trunk | in pruned
Port        Vlans in spanning tree forwarding state and not pruned
SW1#sh int trunk | b pruned
Port        Vlans in spanning tree forwarding state and not pruned
Gi1/0/13    1,5,7-10,22,43,58,67,79,146
Gi1/0/14    1,7
Gi1/0/15    1,7
Gi1/0/16    5,9,43,79
Gi1/0/17    none
Gi1/0/18    none
Gi1/0/19    1,10,146
Gi1/0/20    none
Gi1/0/21    none

Variations of pruning:

SW1(config-if-range)#switchport trunk pruning vlan ?
WORD    VLAN IDs of the allowed VLANs when this port is in trunking mode
  add     add VLANs to the current list
  except  all VLANs except the following
  none    no VLANs
  remove  remove VLANs from the current list