VLAN Trunking Protocol (VTP), like DTP, is a proprietary protocol for Cisco switches. The purpose of VTP is to make VLAN configuration easier by synchronizing VLAN configuration information throughout a VLAN domain. This is done by designating one switch as the VTP server, and letting it handle the addition, deletion, and renaming of VLANs throughout the domain.

The three available modes in a VTP domain are as follows:

• Server: This is the default mode. When changes are made on a VTP server, the changes propagate to all other switches on the domain. The VTP server is also responsible for creating VTP advertisements, which make this propagation possible.
• Transparent: If a switch is in transparent mode, changes made to the configuration will affect only that one switch. Transparent switches cannot create VTP advertisements, but they can forward VTP advertisements.
• Client: Switches in client mode cannot make any changes to the configuration, but they can send VLAN information in their databases to other switches. They can also forward VTP advertisements to other switches.

Obviously, the larger your network gets, the greater the potential is for VTP to make your life easier, since instead of configuring dozens or even hundreds of switches, you will only have to configure a single switch. In addition, VTP has a feature called VTP pruning, which forwards broadcast and unknown unicast messages to switches only if the switch has ports for the VLAN on which the broadcast/unicast messages are being sent. This makes for more efficient use of trunk bandwidth.

Configuring VTP requires only a few additional commands. Since we are making changes for the entire switch and not just a port or range of ports, we can use global configuration mode:

1. First, enter global configuration mode:

Switch# configure terminal

2. Next, set the switch as a VTP server, with the following command:

Switch (config)# vtp mode server

3. You can also put the switch in client mode or transparent mode:

Switch (config)# vtp mode client
Switch (config)# vtp mode transparent

4. To set the domain name, use this command:

Switch (config)# vtp domain <domain_name>

Here, <domain_name> is the domain name to which you want to set  the domain.

5. You can set a password with the following command:

Switch (config)# vtp password <password>

6. To set the VTP domain to VTP version two, type the following (the current version is version three):

Switch (config)# vtp v2-mode

7. Finally, to enable pruning, use this command:

Switch (config)# vtp pruning

The remainder of the configuration is identical to the steps outlined earlier. You must configure both the access ports and trunk ports, create the VLANs, and assign ports to them. By using VTP, however, configuration will be much easier, and it will be easier to make changes when necessary.