Does VTP need an untagged VLAN to function?

chris · ‎02-08-2010

I have a trunk link between a 6509 and 3750, no native vlan is set on the interface.

Only one vlan is allowed on the trunk - switchport trunk allowed vlan 300.

One switch is VTP server one is to be client.

Will VTP communicate between the 2 switches if so how?

I have also read you cannot remove Vlan 1 from the TRUNK, the output from show in trunk appears to tell me i have removed VLAN 1.

I have tried looking for docs on VTP and native vlan but can't find any relevent to my question.

Thanks

glen.grant · ‎02-08-2010

If no native is specified then it is vlan 1 by default . Vlan 1 does not have to be allowed across the trunk inorder things like cdp ,vtp etc to work .Vlan 1 will just not carry any data on vlan 1 Just match what is allowed across the trunk on both sides..

Jon Marshall · ‎02-08-2010

chris@icl.net

I have a trunk link between a 6509 and 3750, no native vlan is set on the interface.

Only one vlan is allowed on the trunk - switchport trunk allowed vlan 300.

One switch is VTP server one is to be client.

Will VTP communicate between the 2 switches if so how?

I have also read you cannot remove Vlan 1 from the TRUNK, the output from show in trunk appears to tell me i have removed VLAN 1.

I have tried looking for docs on VTP and native vlan but can't find any relevent to my question.

Thanks

The simple answer is no, VTP does not require an untagged vlan to work. As Glen says the default native vlan ie. the untagged vlan, is vlan 1. You can remove vlan 1 from a trunk and it is still used to transmit control protocols CDP/VTP/PaGP. So if you change the native vlan from vlan 1 then all VTP traffic being sent on vlan 1 will be tagged. If you leave the native vlan as is then VTP traffic will be untagged.

You can clear the native vlan from both ends of a trunk link whether it is vlan 1 or another vlan and VTP will still work.

Jon