Hello Chris
Initially, a switch will have the following default parameters for VTP:
- VTP operating mode: Server
- VTP Domain Name: Null
In such a case, VTP is active, but switches will not actively create any VTP associations with any other switches simply because the domain has not been configured. When all switches have a domain of NULL, it is as if VTP is not functioning.
However, this can still be a dangerous situation, because if a rogue switch is added which has a VTP domain configured, it will start to send VTP messages, and any switch on the network that still has a NULL domain, will automatically adopt that domain as well.
You can’t disable VTP as a feature, but you can ensure that a switch never participates in any VTP domain that may appear on the network by simply changing the VTP mode to transparent like so:
Switch(config)#vtp mode transparent
This ensures that any VTP messages received will be ignored.
I hope this has been helpful!
Laz