Lectures on LAN Switching - Part 11

VLAN Trunk Protocol (VTP)

Before we go any further, let's discuss a feature that will help us manage VLANs in an ever expanding LAN network - VLAN Trunk Protocol, or simply, VTP.

This is one of my favorite interview questions before when I'm still conducting applicant interviews. Most will answer that it has something to do with Trunk configuration and management, rather than with VLANs. But that's just until they get smarter. =P

Moving forward, just imagine configuring and managing a new network with around 100 Catalyst Switches. To complicate the configuration a bit, every Switch needs to be configured with 100 VLANs. Imagine doing that repetitively on all 100 Switches. Hard right? =)

Isn't it more productive if I can just automatically replicate any VLAN configuration I make on one Switch to the other 99 Switches? Well, that's the main beauty of VLAN Trunk Protocol. VTP minimizes the administration overhead in Switches, particularly in configuring and managing VLANs across a Switched network.

You just need to configure at least one Switch as a VTP server, and the VLANs present on a VLAN Database will be replicated through all other Switches in the same VTP Domain. This will significantly reduce the time spent configuring VLANs on all your Switches. One downside though, VTP is a Cisco-proprietary protocol. You can only expect in on Cisco Catalyst Switches, and not anywhere else.

You may ask what the 'Trunk' in VTP is all about if this is only about VLAN management. Apparently, VTP will only work through Trunk connections. Any links that is only passing traffic from a single VLAN won't be able to pass through VTP advertisements.