vtp domain mismatch

alliasneo

Hey guys,

Just working on some VTP commands and I have set just one switch to a VTP server and am changing everything on here so it feeds down to the other switches. Whenever I add a vlan it all works ok it updates the config revision number and add the vlans to the other switches but whenever I change the domain name I get:

00:05:50 %DTP-5-DOMAINMISMATCH: Unable to perform trunk negotiation on port Fa0/1 because of VTP domain mismatch.

Is this true of VTP and I would have to manually change the domain name on each switch or have I not configured something?

SharkDiver

You would definitely have to change the domain name manually. That is how the switches know whether or not they are supposed to share information with each other. If you change the domain name, you have told them to be in separate VTP groups and they will no longer share info.

dtlokee

The error message you are receiving is related to Dynamic Trunking Protocol (DTP) basically stating that it can't negotiate a trunk because the neighboring switch is in a different VTP domain. Generally it is a bad practice to allow trunks to dynamically negotiate and you can resolve the error in a few ways:

1. Correct the VTP domain name on the neighboring switch so it matches, to be safe I would recommend setting it to VTP transparent to reset the revision number to 0 before adding it to the domain then set it back to server or client depending on your design.
2. Disable DTP with the "switchport nonegotiate"
3. Hard code the interface as trunk by setting the encapsulation mode (if the switch supports dot1q and ISL) and "switchport mode trunk"

MrXpert

those domain mismatch messages can be annoying but I tend to intentionally set them up so that I get domain mismatch messages just to help my understanding. I usually then correct it by verifying ports are manually configured to trunk and also make sure that I use the switchport nonegotiate command. You can verify both of these by using the "Show interface {number here} switchport" command. It will tell you the admin and operational modes as well as whether DTP is turned on or off.
If it is a transparent switch I am getting the error on and the domain is different then this gets rid of those messages. Alternatively I make sure all switches are in the same case sensitive domain.

alliasneo

thats great. As soon as I manually go in and change the domain names over it all works perfectly. Thanks everyone