VTP domain mismatch

[tedauction]

Hello, we had a trunk go down with the following error log:

 %DTP-5-DOMAINMISMATCH: Unable to perform trunk negotiation on port Gi0/25 because of VTP domain mismatch.

The reason for this was a change of VTP domain name on one switch.

The thing I cannot understand is that both switches had VTP mode transparent before making this change.

I am now thinking that this was due to one switch not having the command 'switchport mode trunk' explicity defined on it's trunk interface, therefore even though VTP was in transparent mode on both switch sides of the trunk, the lack of 'switchport mode trunk' on one side still caused the trunk to fail when the VTP domain name was changed on the opposite side.

Do you agree with this ?

Thank you kindly.

[cofee · Accepted solution]

Please read this blog for clear explanation.

http://packetlife.net/blog/2008/sep/30/disabling-dynamic-trunking-protocol-dtp/

[Demla.jatin1]

The very first thing you should do is to check the whether the port is in access or trunk mode by using the command show interfaces switchport, and please make sure that the port is not in the dynamic auto mode because this way it will not negotiate the trunking if even the other port is trunk port.

The next thing you can do is make it trunk port specifically or you can configure the command

switchport mode dynamic desirable, this command will make sure that this port can negotiate with the trunk ports now.

"Do you agree with this? " and yes i totally agree with your opinion as well.

** Please rate the answer its helpful **

[Julio E. Moisa]

Hi

That is correct and make sense when Trunking negotiation is enabled, this link could be useful to get more details. You could configure switchport nonegotiate under the trunk interface. 

https://supportforums.cisco.com/document/14571/dtp-5-domainmismatch-error-message-displayed-logs-cisco-catalyst-switches

Hope it is useful

:-)

[Joseph W. Doherty · Accepted solution]

VTP transparent mode doesn't completely turn off VTP, it's just that device won't use the VTP VLAN database.  With the right conditions, VTP transparent mode can forward the VTP VLAN database.  So, VTP transparent mode complaining about a VTP domain can make sense.

On the other hand, if you have a device that supports VTP off mode, and that's what's active, I wouldn't expect it to complain about a VTP domain mismatch.