Difference between vty pruning and allowed vlans command

Unanswered Question
Nov 21st, 2007

Is there a difference between vtp pruning and controlling the vlans allowed using the switchport trunk allowed vlan vlan-list?

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cisconoobie Wed, 11/21/2007 - 14:14

VTP pruning removes the unnecessary vlans from the trunk but does not remove the spanning-tree instance that is still running for that vlan.

using the trunk allowed command totally removes it from trunk.

anand.dahiya Wed, 11/21/2007 - 21:58


Well the "switchport trunk valn vlan list" only allowed the trafic for specific vlans that u add to the vlan list in the above commant where as if enable the vtp prunning that only forward the traffic if same vlan exist on both the swith for eg. if one switch is having vlan 2,3,4 and another have vlan 2,5,6 in this scenerio only vlan 2 trafgfic can cross the trunk.


Edison Ortiz Wed, 11/21/2007 - 22:19

They both perform the same task. One is done dynamically (you enable vtp pruning in the entire vtp domain) while the other is a manual process and it's a per switchport configuration.

If you are running vtp transparent mode, you only have one option, that is - you need to do it manual way since you don't have a vtp domain.

Jon Marshall Wed, 11/21/2007 - 23:26


Just to clarify, as one of the other posters pointed out there is a slight difference in that vtp pruning will stop any traffic being sent down a trunk link to a switch which has no ports in that vlan.

Vtp allowed ... defines which vlans are allowed across the trunk so in that sense they are the same. But unlike VTP pruning, when you remove a vlan off the trunk the STP instance for that vlan still runs but not down to the switch that is at the other end of the trunk. So in effect you can control across which switches STP is run per-vlan.



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