What happens......(VTP Question)

Unanswered Question
Sep 21st, 2007

If you have 2 switches, both in the same VTP domain and both VTP Servers. What happens if you add a VLAN on 1 switch, does it show on the other?

I have this problem too.
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Kevin Dorrell Fri, 09/21/2007 - 07:15

Yes it does, as long as the switches are trunked together, the VTP domain matches, and the VTP password (if any) matches.

Protocol-wise there is no difference between a VTP server and a VTP client. The only operational difference is that the client will not allow you to use the CLI (Command Line Interface) to change the list of VLANs.

Kevin Dorrell


rwamstutz Tue, 09/25/2007 - 11:48

can I change a VTP Server to a VTP Client while in production?

l.mourits Tue, 09/25/2007 - 12:34

Yes, you can, allthough you will have to give it some thoughts, because you should be aware that if you set your last vtp server to client mode all other vtp clients will loose there vtp server (which is bad, as they will loose all vlans). If you still have another vtp server you can safely set the other vtp server to cient mode.



Kevin Dorrell Tue, 09/25/2007 - 19:25

Sorry, I disagree. If you take a VTP server on its own, and change it to a VTP client, will it will lose its VLANs. I don't think it needs a server to be active on the network all the time - only when updating.

As I was saying, the only difference between a server and a client is in the CLI. Note this: a client still transmits advertisments, and can still update the network.

Try this experiment: take a network of two switches, A and B, both VTP srver, and create some VLANs. Remove the link between them, and change switch A to VTP client. Does switch A lose the VLANs? I don't think so.

Then go to switch B, which is still VTP server, and remove half of the VLANs. The VTP revision level goes up. Change switch B to VTP client and then reconnect it to switch A, which is also VTP client. You now have two VTP clients connected together. What has happened to your VLANs? I think switch B will learn the new config from switch A.

Kevin Dorrell


l.mourits Tue, 09/25/2007 - 23:31


I agree with what you say, the thing though is that if all swicthes are VTP clients and one reloads, it will come up and configure itself as VTP server. As long as another client still holds a higher revision number there is nothing wrong, but problems may arise later on. I would always ensure there is at least 1 VTP server in your VTP domain.



paul.matthews Tue, 09/25/2007 - 23:36

why on earth would yo set *all* switches to client mode? If you do that, the network will work, all will have all the vlans, but you won't be able to add/delete vlans.

Normally one would leave core switches as servers, so that VLANs can be added/removed from the servers.

rwamstutz Wed, 09/26/2007 - 04:38

Ok, what if, Both are VTP Servers, and I decided to add a switch to 1 of the switches that is a VTP Server. What happens to the config or the VTP Setting for that switch after a switch is merged to form a stack?

l.mourits Wed, 09/26/2007 - 04:41

If you add a switch, configured for VTP client it will simply receive the vlan info from the VTP server, that is, if the vtp domain matches and the revision is not higher then the vtp server's revision.


rwamstutz Wed, 09/26/2007 - 04:44

What if you add a switch, that is configured as a VTP Server with no domain, to another switch that is configured as a VTP Server for domain1 to form a stack? Which VTP Server takes precedence?

l.mourits Wed, 09/26/2007 - 04:51

I would strongly recommend to avoid having two vtp domains in one switch environment. What is it you are trying to achieve. It souns like transparant mode is the mode to go for you instead of client or server.

rwamstutz Wed, 09/26/2007 - 04:56

yea, I understand that. I am waiting to merge two switches for form a switch stack. I am curious to know what happens to the configs on switch 1 and the configs on switch 2 when they are formed to create a switch stack? does everything reset and new configs need to be loaded?

l.mourits Wed, 09/26/2007 - 05:15

So, basically your question is not aboput vtp but about stacking behavior. In that case I would recommend reading the following:


It boils down to that the elected master will be leading in config, so you will definately loose one of the vtp domains in this case.




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