Each switch can use one of four different VTP modes:
- VTP client mode – a switch using this mode can’t change its VLAN configuration. That means that a VTP client switch cannot create or delete VLANs. However, received VTP updates are processed and forwarded.
- VTP server mode – a switch using this mode can create and delete VLANs. A VTP server switch will propagate VLAN changes. This is the default mode for Cisco switches.
- VTP transparent mode – a switch using this mode doesn’t share its VLAN database, but it forwards received VTP advertisements. You can create and delete VLANs on a VTP transparent switch, but these changes will not be sent to other switches.
- VTP mode off – similar to VTP transparent mode, with a difference that a switch using this mode will not forward received VTP updates. This command is supported only in VTP V3.
As mentioned above, all switches are configured as VTP servers by default. This is fine in smaller networks without too many VLANs and VLAN changes, since all VLAN information can easily be stored in each switch’s NVRAM. However, in larger networks, it is recommended to specify a couple of higher-quality switches to serve as VTP servers. All other switches in the network should be set up as VTP clients.
Consider the following example:
We have a simple network of three switches. SW1 is configured as VTP server. After the VLAN 5 is created on SW1, this switch will notify the connected switch (SW2) about the created VLAN. SW2 will receive the update but, since it uses the VTP transparent mode, it will not create this VLAN in its configuration. However, it will forward the VTP update to SW3. Since SW3 is configured as VTP client, it will process the update and create VLAN 5.