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Enabling VTP Prunning

Posted on 2014-10-26
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Last Modified: 2014-10-26
I am trying to undersand how VTP pruning works when enabled at the configuration level.
I have Enabled VTP Prunning at the Global Configuration, then assigned some interfaces on Switch1 and Switch2 to different vlans.

However there is Vlan on SW1 that has no ports assigned to it is still showing on SW2 and vice versa

Here VLan 33 has no interfaces assigned to it and it still showing in SW1
SW1#sh vlan br

VLAN Name                             Status    Ports
---- -------------------------------- --------- -------------------------------
1    default                          active    Et0/3
10   VLAN0010                         active    
11   VLAN0011                         active    
20   VLAN0020                         active    
33   VLAN0033                         active    
40   VLAN0040                         active    Et0/1, Et0/2
1002 fddi-default                     act/unsup
1003 trcrf-default                    act/unsup
1004 fddinet-default                  act/unsup
1005 trbrf-default                    act/unsup
SW1#

Here Vlan 40, has no interfaces assigned to it , but is showing :
SW2#sh vlan brief

VLAN Name                             Status    Ports
---- -------------------------------- --------- -------------------------------
1    default                          active    Et0/2, Et0/3
10   VLAN0010                         active    
11   VLAN0011                         active    
20   VLAN0020                         active    
33   VLAN0033                         active    Et0/1
40   VLAN0040                         active    
1002 fddi-default                     act/unsup
1003 trcrf-default                    act/unsup
1004 fddinet-default                  act/unsup
1005 trbrf-default                    act/unsup
SW2#
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Question by:jskfan
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by:Don Johnston
Don Johnston earned 500 total points
ID: 40405489
Pruning does not delete a VLAN from a switch.  It removed the VLAN from the allowed VLAN list on a trunk.  

So if you issue a "show int trunk" on the remote switch, you should see the VLAN not listed in the "Vlans in spanning tree forwarding state and not pruned" section.
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Author Comment

by:jskfan
ID: 40405536
I see the Output below. What do they mean by:
 Port        Vlans in spanning tree forwarding state and not pruned
Et0/0       1,33


SW1#sh interfaces trunk 

Port        Mode             Encapsulation  Status        Native vlan
Et0/0       on               802.1q         trunking      1

Port        Vlans allowed on trunk
Et0/0       1-4094

Port        Vlans allowed and active in management domain
Et0/0       1,10-11,20,33,40

Port        Vlans in spanning tree forwarding state and not pruned
Et0/0       1,33
SW1#

Open in new window


SW2#sh interfaces trunk

Port        Mode             Encapsulation  Status        Native vlan
Et0/0       on               802.1q         trunking      1

Port        Vlans allowed on trunk
Et0/0       1-4094

Port        Vlans allowed and active in management domain
Et0/0       1,10-11,20,33,40

Port        Vlans in spanning tree forwarding state and not pruned
Et0/0       1,40
SW2#
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Don Johnston earned 500 total points
ID: 40405549
I see the Output below. What do they mean by:
 Port        Vlans in spanning tree forwarding state and not pruned
Et0/0       1,33

The only VLANs able to cross the trunk are VLANs 1 and 33.

Which means 10, 11, 20 and 40 will not be carried over that trunk.
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Author Closing Comment

by:jskfan
ID: 40405577
Excellent!!
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