Default VTP Domain

[daudparvez]

VTP is operative on all CISCO Switches by default. Every CISCO Switch is a member of the default NULL VTP Domain. When a Switch is connected to an existing network, it learns the domain from the VTP Advertisements and configures it.

Now the question is if we haven't configured  VTP Domain on any of the switch and all switches are members of the default NULL VTP Domain, then will VTP be functional, wethere VTP messages be sent, recieved and acted upon?

And one more question, can we disable VTP or not?

Best Regards,

Daud Parvez.

[Peter Paluch]

Daud,

If I remember correctly (and I hope other friends here will correct me if I am wrong!), there are no VTP messages sent from switches if their VTP domain is empty (i.e. NULL). As soon as you configure one switch to a non-NULL VTP domain name, however, it will propagate this name to all other switches whose name is still NULL. As a consequence, in a clean network with all switches having the VTP domain empty and trunks properly configured, renaming the VTP domain on a single switch will cause all switches to adopt this new domain name.

This will happen only once when the original VTP domain name was NULL. Afterwards, new domain name changes have effect only on the switch that is currently modified manually.

With VTPv1 or VTPv2, there is no option of turning VTP off. You could set the device to VTP Transparent mode which would prevent it from actually participating in VTP, and if you additionally set the transparent device to a different domain name, it will not even pass VTP packets.

In VTPv3, there actually is an option of deactivating the VTP, either on global or on a per-port basis.

Best regards,

Peter