Virtual Local Area Network Trunking Protocol or VTP is CISCO proprietary protocol in maintaining configurations on a Virtual Local Area Network’s or VLAN’s by managing and provide consistency and changes throughout the VLANed network. It can add, delete and modify changes or manage the configuration process with ease as well during troubleshooting.
There are three (3) modes that you can configure on a CISCO switch and these are called VTP modes:
Server Mode – this is where your VLAN’s can be configured, created, deleted, and modified. It advertises any VLAN information to other switches that have the same domain name and the best way to select a VTP server is somewhere the center of your network. Be advise that the best practice is to have a unique domain name for your VTP configurations.
Client Mode – This only accepts the VLAN information passed by the server with the same domain name and passed the information to other client VTP switches. The changes of any VLAN information from this mode cannot be change, however you can by configuring it to server mode but this isn’t a good practice.
Transparent Mode – A mode wherein it doesn’t modify its VLAN information from the Server but it only passes the VTP information or advertisements.
The advertisement of VTP is through a trunking protocol 802.1q and it is sent every five (5) minutes, which is called the Summary advertisement, over the default VLAN which includes the configuration revision number, domain name, and other information. It doesn’t include the VLAN information. A Subset advertisement follows when any revision or modification happens and changes on the configuration on the VTP client’s will automatically add its revision number and information to its VLAN Database. Lastly, the Advertisement request message is sent when a trunk is up from a neighboring VTP client switch.
Another VTP concept is VTP Pruning it is using appropriate trunk interfaces or specific trunking interfaces that are only to be used for a specific VLAN to avoid flooded frames, thus minimizing VLAN advertisements.