Turning VTP off with pruning

[jc482065]

Hi,

We are planning to disable legacy config of VTPv2 on a network. Pruning is enabled on the domain. When we attempted to run "VTP mode off" on a switch at the edge of the network, we found that the upstream switch appeared to prune all the VLANs from the link (seen with an output of "show interface Tex/x/x trunk". However, when running VTP in transparent mode on the same switch, it did not lose connection and VLANs were being trunked as normal.

Why does VTP pruning prune VLANs when connected to a "VTP mode off" switch but not a "VTP mode transparent" switch? I thought both did not process VTP frames. We don't want to make a global change to the VTP domain (i.e. turn pruning off) until the edge switches are not running VTP.

[Torbjørn · Accepted solution]

VTP mode transparent is as described "transparent" to the VTP domain. It will not process VTP locally but it will relay VTP between other switches who are in server or client mode. When you put an intermediate switch in "off" mode it will not relay VTP messages, resulting in VLANs being pruned from upstream trunks.

[Joseph W. Doherty]

I'm addition to @Torbjørn describes, as part of your removal of VTP, you can first disable VTP pruning (and manually prune).

[jc482065]

The switch we tested on was not an intermediate switch, it was at the edge of the network but connected upstream to a VTP client. I thought both "transparent" and "off" switches don't send VTP so why does the upstream switch prune on one and not the other?

We don't want to make domain-wide changes.

[Joseph W. Doherty]

Again, as @Torbjørn described, VTP transparent mode should relay VTP.

Don't have a complete description of your two VTP cases, but an issue I bumped into years ago (and if I recall it correctly), VTP pruning was enabled and it pruned off a VLAN being used downstream.  What the issue cause was, an intermediate switch was not using the VLAN, itself, so its upstream switch's VTP pruned the VLAN being used one transit switch away. The other facet that surprised us, VTP pruning was rather slow, recall it took about 30 seconds to prune, so at first everything was operating as expected.

Again, unclear any of above would apply to your observed VTP pruning behavior