VTP (VLAN Trunking Protocol) is a Cisco proprietary protocol used by Cisco switches to exchange VLAN information. With VTP, you can synchronize VLAN information (such as VLAN ID or VLAN name) with switches inside the same VTP domain. A VTP domain is a set of trunked switches with the matching VTP settings (the domain name, password and VTP version). All switches inside the same VTP domain share their VLAN information with each other.
To better understand the true value of VTP, consider an example network with 100 switches. Without VTP, if you want to create a VLAN on each switch, you would have to manually enter VLAN configuration commands on every switch! VTP enables you to create the VLAN only on a single switch. That switch can then propagate information about the VLAN to every other switch on the network and cause other switches to create it. Likewise, if you want to delete a VLAN, you only need to delete it on one switch, and the change is automatically propagated to every other switch inside the same VTP domain.
The following network topology explains the concept more thoroughly:
On SW1, we have created a new VLAN. SW1 sends a VTP update about the new VLAN to SW2, which in turn sends its VTP update to SW3. These updates will cause SW2 and SW3 to create the same VLAN. You can see how this simplifies network administration – the engineer only had to log in and create the VLAN on the first switch. Other switches have created the same VLAN automatically.
Three VTP versions are available – V1, V2, and V3. The first two versions are similar except that V2 adds support for token ring VLANs. V3 adds the following features:
- enhanced authentication
- support for extended VLANs (1006 to 4094). VTP versions 1 and 2 can propagate only VLANs 1 to 1005.
- support for private VLAN
- VTP primary server and VTP secondary servers
- VTP mode off that disables VTP
- backward compatibility with VTP V1 and V2
- the ability to be configured on a per-port basis
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