How to Configure VTP pruning

Unanswered Question
May 11th, 2009

Hi I wish to config vtp pruning but only on some trunks. i have 70 vlans and only want vlans 1,42 and 666 active. Please can some confirm this is the correct method:

Core switch:

switchport trunk pruning vlan add 1,42,666

Does this by default stop all other vlans?

Access switch:

Do i do any configuration on this?

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network_team Mon, 05/11/2009 - 05:20


Thanks for this just to confirm this command is all i need to allow the vlans mentioned. I do not wish to enable pruning on a global level and only want to allow the once stated.

Can you also confirm the command is as i believe: allowing the access for the vlans?

Jon Marshall Mon, 05/11/2009 - 05:28

Vlan pruning is a global setting. And if you only want to allow certain vlans on certain trunk links then vlan pruning is not the correct approach.

To control which vlans are allowed on the trunk link you should use the "switchport trunk allowed ..." command on both ends of the trunk -


network_team Mon, 05/11/2009 - 05:38


Do i need to apply this command:

switchport trunk allowed 1,44,666

On both sides of the trunk i.e the core and access?

I assum restricting vlans this way

still improve the network performance ?

Jon Marshall Mon, 05/11/2009 - 05:46

It depends on what is allowed on the trunk already. Using the switchport allowed vlan add command only adds to the existing list so assuming all vlans are allowed you need to remove most vlans from the link.

switchport trunk allowed vlan remove 2-43,45-665,667-1005

on both ends of link.

Note you can check which vlans are allowed by doing "sh interface trunk". I would recommend making the change out of core production hours.

The other way to do it -

switchport trunk allowed vlan remove all

switchport trunk allowed vlan add 1,44,666

again you definitely need to do this out of hours.


network_team Mon, 05/11/2009 - 06:31

Hi please review the below i entered:

switchport trunk allowed vlan remove 2-43,45-665,667-1005

on both ends of the core and switch

switchport trunk encapsulation dot1q

switchport trunk allowed vlan1,44,666,1006-4094

switchport mode trunk

Port Mode Encapsulation Status Native vlan

Fa2/0/48 auto n-802.1q trunking 1

Port Vlans allowed on trunk

Fa2/0/48 1,44,666,1006-4094

Port Vlans allowed and active in management domain

Fa2/0/48 1

Port Vlans in spanning tree forwarding state and not pruned

Fa2/0/48 1

the remove all does not work. does the above look correct?

Jon Marshall Mon, 05/11/2009 - 06:40

"Port Vlans allowed on trunk

Fa2/0/48 1,44,666,1006-4094"

Okay, you also have extended vlans on your trunks so

switchport trunk allowed vlan remove 1006-4094

then only vlans 1,44,666 should be left which is what you want.

Note that according to the output -

Port Vlans in spanning tree forwarding state and not pruned

Fa2/0/48 1

you don't actually have a vlan 44 or 666 at the moment.


network_team Mon, 05/11/2009 - 06:51

Excellent thanks i am on a test lab just checking what performace issue i may have when adding and taking away vlan's. Are you aware if this change could riple the whole network or just the connection from point to point trunk to trunk?

Jon Marshall Mon, 05/11/2009 - 07:11

I don't have a lab to test with but removing vlans from trunks could well have a knock on effect to STP and cause recalculations, hence the reason i suggest out of hours.


network_team Mon, 05/11/2009 - 07:14

This could cause me a slight problem as we make vlan changes on a daily basis and need to do this during working hours. Would pruning provide me with the function on applying changes during the day. I would like to have some kind of control and not let this be a automated thing?


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