Cisco Certification Exam Review:

VLAN Trunking Protocol (VTP)

By Chris Bryant, CCIE #12933

You recall from your CCNA studies that VTP allows a network's switches to have a consistent view of the VLANs in the network. Other VTP fun facts:

VTP is a Cisco-proprietary messaging protocol.

VTP runs at Layer 2 of the OSI model.

VTP is a multicast protocol (destination 01-00-0C-CC-CC-CC, the same used by CDP).

A switch can be in only one VTP domain.

Once you get VTP up and running, it can run for a very long time with no additional configuration, but every once in a while you can run into trouble getting started.

In my experience, VTP problems really come down to two things: password and mode misconfigurations. I'm not big on using VTP passwords, since they're about as non-secure as it gets:

SwC#show vtp password
VTP Password: CCIE

But if you didn't know how to find a VTP password, now you do! You recall from your CCNA studies that we've got three different VTP modes - server, client, and transparent - and that VLANs cannot be created on a VTP client. The switch tells us that, but Cisco exams probably will not. : )

SwC(config)#vlan 100
VTP VLAN configuration not allowed when device is in CLIENT mode.

To your success,

Chris Bryant

CCIE #12933

chris@thebryantadvantage.com