Configure VTP domain and password

[johnlloyd_13]

hi,

i'm in the midst of standardizing our switch fabric.

i haven't touched LAN switch for some time and got a bit rusty.

my question, is configuring VTP domain name and password will cause STP re-calcaulation/short outage?

i audited some switch don't have VTP domain name and passwords and would like to add them.

i would like to lab soon but we have a mix of old and new switch so it might take some time to do it.

[dejan_jov1]

Hi,

VTP is used so that we have consistency of VLAN information across VTP domain. That means if you add a switch to an existing VTP domain the switch will just be configured with VLANs from VTP server. I don't see any reasons why would the STP recalculate itself.

[johnlloyd_13]

now you've mentioned it, i now recall VTP is for VLAN database replication.

to re-phrase my question, so it's safe to configure the VTP domain and password on the current L2 topology?

do they need to be same VTP role (server, client, transparent)?

[dejan_jov1]

I found this document, it could help:

http://www.cisco.com/c/en/us/support/docs/lan-switching/vtp/81682-vtp-migration.html

You should be careful when adding a switch to VTP domain, if the revision nummber on new switch is higher than on VTP server it will overwrite the VLAN database (even if added ass client!)

You should see who is the Server in domain and to be shure that revision number on new switch is lower than on VTP server and to add the VLANs on VTP server. (if you have VLANs on new switch that don't exist on VTP server). You should add new switch as client.

[johnlloyd_13]

i'm not adding a new switch into the network.

my original question is regarding VTP domain and password to be configured on the current switches in the topology. so is it safe or not to add these commands?

[dejan_jov1]

Configure one Switch as VTP server with password and domain command (choose a core switch) and make shure that you have all Vlans on it. Add one after another switch to VTP domain as client (also with domain and password) and as you add them make shure that the revision number is lower than on VTP server.

[paul driver]

Hello John
Yes it will be safe to do so - however please note doing this will make those switches able to receive valid vtp advertisements from the vtp server which will overwrite lower vtp revison numbered switches.

I would suggest before you make the changes on the switches in question change their vtp mode to transparent and back to client just incase they have a higher revision number than the current  valid vtp server of the domain.( refers vtp version 1-2 only)

res
Paul

[johnlloyd_13]

hi paul,

thanks for diving in and for the tip!

i need to be careful with these changes although it looks simple, it could be deadly. i don't want to blow up any switch network and cause any outage.

what if the switches are all VTP server, does it make any difference or do i disregard the VTP revision number?

once i get all info i need, i'll lab this up before making changes on our switch network.

[paul driver]

Hello John

what if the switches are all VTP server, does it make any difference or do i disregard the VTP revision number?

The revision number is the key - if the switches you want to add to the domain have a higher revision number (either in Server OR client mode) then your current active vtp primary server and all its clients will get overwritten. (only refers to vtp version1/2 )

So as a precaution just simply change the vtp mode of the switches you want to add to the domain to transparent and then back to either client of server ( I would suggest client) and this will reset the revision number to 0

One more thing vtp ver 1 & 2 dont work with each other on switches in the same VTP domain. So before your change just make sure they are all running the same ver number.

res
Paul

[johnlloyd_13]

thanks for your inputs!

guess i'll lab this up some few scenarios before making changes.

[Joseph W. Doherty]

VTP, itself, doesn't interact with STP.  However, it's possible to make VLANs known or unknown to a switch, via VTP, and if you do that, you could impact the L2 topology and impact STP.  (You can also drop hosts from your topology too.)

BTW, with VTP versions 1 or 2, the only difference between a "server" and a "client", the former allows you to make configuration changes.  "Under the covers" they operate alike.  V3 VTP is  different.

Also BTW, with VTP versions 1 or 2, switches with a NULL domain can flip to a named VTP domain without your setting it.  VTP passwords, though, require manual configuration.