VTP server : advertising a vlan that should not be on the trunk

Question

On a vtp server, when configuring the trunks, I am not allowing a certain vlan on that trunk.

However it still gets advertised by the vtp server. It cannot be used, but I am wondering if there is a way to configure the vtp server to not advertise that vlan on that trunk ?

Answer 1

The purpose of VTP is to ensure the VLAN database on all devices in that VTP domain is the same.

There's no way to limit which VLANs a VTP server advertises to its clients, and that could be undesirable anyway. Consider these three switches connected via trunk links:

SwitchA == SwitchB == SwitchC

SwitchA is your VTP Server and switches B & C are VTP Clients. You may not want VLAN 10 to be propagated from SwitchA to SwitchB, but you may still wish to use VLAN 10 on SwitchC. If you were somehow able to stop VLAN 10 being sent to SwitchB it would be subsequently not advertised to SwitchC and not available for use.

Answer 2

To do this, you would configure VTP Pruning. It's worth noting that VTP seems to be going out of style due to the risk of misconfiguration resulting in massive outages. It's much safe to not run VTP at all by configuring all switches to be in transparent mode.

Answer 3

VTP pruning is used to restrict flooded traffic to trunk ports that must be used to reach the destination (trunks that link switches that have ports that are members of the same VLAN).

Restricting trunk links to certain VLAN's affects VLAN client traffic for the restricted VLAN's, not VTP traffic. I don't think what you're looking to do is possible.

Answer 4

In short, no.

A VTP server will advertise all VLANs configured on the switch via VTP in an attempt to maintain a synchronized VLAN database on all switches in the particular VTP management domain.

VTP pruning allows a switch to dynamically indicate to a remote switch on the other side of a trunk that the traffic within a [inactive] VLAN not be forwarded across a trunk -- based upon whether or not a switch has ports currently active within the VLAN. Note that this does not remove the VLAN from the VTP management domain, just makes the VLAN inactive, hence pruned on the trunk.

You can see the difference between the management domain and not pruned VLAN's within the management domain the following command.

show interfaces trunk