It's also probably a good idea to mention to our readers that the Virtual Trunk Protocol is used when connecting multiple LAN switches together to form network backbone. In such networks, because there are usually a lot of network nodes (computers, network devices, etc.), we use VLANs to break the network into smaller logical networks – thus increasing the network security, but also allowing us to better control the resources available to each VLAN.
VLANs require to be configured on each VLAN-aware switch that will participate in the network. This means that if you've got nine different VLANs and 25 switches, you're going to have to configure each of the nine VLANs on all 25 switches – a nightmare for any network engineer!
The other alternative is to use the VTP. VTP in the above case is definitely your best friend, as once configured on the core switches, it will then automatically propagate all VLAN information to all network switches, saving you from the need of their configuration!
Now, regarding the 802.1q encapsulation protocol and its associated VLAN ID's, 1002 thru to 1005 are not reserved by the protocol. In fact, these VLAN ID's are reserved for FDDI and Token Ring and cannot be deleted from the switches system.
I've actually spent quite a bit of time and research on the VLAN/VTP topic and you can obtain a great deal of information and example here.
This was first published in March 2005