VTP Mode from Client to Server

[ahmad82pkn]

Hi i have a production network. My Core1 is down that was VTP server.

Now i want to make my Core 2 (that is currently VTP client) to ack as VTP server.

if i simply change the mode to VTP server.

Will it cause any issue on live network?            any experiences?

[JohnTylerPearce · Accepted solution]

The VLANs learned from the VTP Server are held in vlan.dat.  If you configure 'vtp mode server' on this

client, then it should propaget information to the other switches in the VTP domain, as long as it has the

highest revision number and the onl VTP server in the VTP domain.

[ahmad82pkn]

Thanx. finally i had no option and your answer was helpful . i changed my Core2 to VTP Server.

and all is good. Revision number remain same ( ii thought it might change to 0 and then again i will need to manually increase it , but that wasnt required ) .

Hence proved changing VTP mode from Client to Server will have no issues and to have it working Server, its Rev number should be greater or equal to any other switch in switching domain.

[JohnTylerPearce]

I'm glad I could help you out. Have a good weekend!

[Joseph W. Doherty]

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The  Author of this posting offers the information contained within this  posting without consideration and with the reader's understanding that  there's no implied or expressed suitability or fitness for any purpose.  Information provided is for informational purposes only and should not  be construed as rendering professional advice of any kind. Usage of this  posting's information is solely at reader's own risk.

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Posting

Actually, VTP server or client both distribute the VLAN database.  Switching from client to server or the converse doesn't impact the distribution or the VLAN database.  The only real difference between them is whether you're allowed to configure VLAN changes on the device.

PS:

If you wondering why have server and client, consider what might happen if you and I make VLAN changes on two different VTP server mode devices at about the same time.  So it's good practice to only have one device in server mode.  If you lose that device, you just select any other client mode device and set it to server mode.

[glen.grant]

  Best practice is to have a couple of vtp servers on your network, specially if you don't regularly backup your vlan.dat file from your vtp server.

[Joseph W. Doherty]

Disclaimer

The   Author of this posting offers the information contained within this   posting without consideration and with the reader's understanding that   there's no implied or expressed suitability or fitness for any purpose.   Information provided is for informational purposes only and should not   be construed as rendering professional advice of any kind. Usage of  this  posting's information is solely at reader's own risk.

Liability Disclaimer

In   no event shall Author be liable for any damages whatsoever (including,   without limitation, damages for loss of use, data or profit) arising  out  of the use or inability to use the posting's information even if  Author  has been advised of the possibility of such damage.

Posting

I would council against such practice, because having more than one VTP server mode may allow a "race condition" update (and every VTP client has a copy of the VLAN database).  It's unlikely, but when or if it happens, adds "fuel to the fire" that VTP is "bad" and shouldn't be used.

I had worked in an environment where someone added a VTP client mode, yes client mode, switch to the production network, and it nicely reset the whole prod L2 VTP.  So, of course, management insisted that VTP be deactivated so that couldn't happen again.

At my current employer, we haven't yet had that happen, but "just to be safe", we're deactivating the VTP "virus".  Also, of course, VTP deactivation makes new joy for VLAN management across multiple switches.

[glen.grant]

    I agree if you have people who don't understand how vtp works it's not a good idea but  we ran a big install  with 2 vtp servers with 80 vlans for 15 years without an issue.  If you don't understand how vtp works and even vtp clients can update the whole vtp domain if it happens to have a higher revision number you should not use it  or if you have no control on who is adding things to your network you also should not use it .   The reason we had 2 servers is if you lose one of the servers you have a backup which has same revision number as the vtp domain. You can then replace the broken vtp server , check the replacement is lower and it should just learn the revision number when it is inserted into the network, and it does work as we handled a hardware upgrade this way and it worked perfectly .

[Joseph W. Doherty]

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

The reason we had 2 servers is if you lose one of the servers you have a backup which has same revision number as the vtp domain.

My understanding is, every VTP client also "backs up" the VLAN database.

You can then replace the broken vtp server , check the replacement is lower and it should just learn the revision number when it is inserted into the network, and it does work as we handled a hardware upgrade this way and it worked perfectly . 

I would expect it to work exactly as you described; perfectly.  However, again my understanding of VTP (until you get to version 3), you could have accomplished the same without even an active VTP server.  In fact, if the failed device was the VTP server, the new device could be defined and added as a VTP server while all other devices were VTP clients.  Also while waiting to replace the failed device, you can "promote" any VTP client to server mode to allow VLAN configuration changes.

Again, once you have more than one VTP server, you expose yourself to a VTP "race condition" update.  This is very unlikely, especially if you do take care making VLAN changes.  (An example being your exposure of having two VTP servers for 15 years, but without an incident.)  But if you're going to go to the trouble of having VTP server vs. client mode devices (I've worked with VTP where all devices were server mode too, without incident), why not take full advantage of avoiding this possible error?  I.e. only allow one device that allows VLAN configuration changes.