We’ve already learned that using VTP makes it is possible to make configuration changes on one or more switches and have those changes automatically advertised to all the other switches in the same VTP domain. In a typical network some switches are configured as VTP servers and other switches are configured as VTP clients. A VLAN created on a VTP server switch is automatically advertised to all switches inside the same VTP domain.
To exchange VTP messages, five requirements must be met:
1. a switch has to be configured as either a VTP server or VTP client
2. the VTP domain name has to be the same on both switches
3. if present, the VTP domain password has to be the same
4. VTP versions have to match
5. the link between the switches has to be a trunk link
Consider the following example network:
We have a network of three switches connected via trunk links. On SW1, we will configure the VTP domain name using the vtp domain NAME command and VTP password using the vtp password PASSWORD commands:
SW2 and SW3 will create the VLAN 30 automatically. We can use the show vlan command on both switches to verify this:
To display the VTP configuration information, we can use the show vtp status command:
The most important field listed in the output above is the Configuration Revision number. This number indicates the level of revision for a VTP packet. Each device tracks the VTP configuration revision number that is assigned to it. This information is used in order to determine whether the received information is more recent than the current version.
Each time you make a VLAN change on a VTP server, the configuration revision number is incremented by one and a VTP advertisement is sent. The switch that receives a VTP packet compares the configuration revision to its own revision. If the configuration revision number in the received VTP advertisement is higher than its own revision number, the switch will overwrite its VLAN configurations with the new information that is being advertised.