VTP

VTP allows you to configure VLANs on a central VTP server switch, and other switches (VTP clients) will synchronize their VLAN database to the server.

It is designed for large networks with many VLANs, so that you don't have to configure each VLAN on every switch.

It is rarely used, and it is recommended that you do not use it.

There are three VTP versions: 1, 2, and 3.

There are three VTP modes: server, client, and transparent.

Cisco switches operate in VTP server mode by default.

Servers/Clients

Servers

Can add/modify/delete VLANs.

Store the VLAN database is non-volatile RAM (NVRAM).

Will increase the revision number every time a VLAN is added/modified/deleted.

Will advertise the latest version of the VLAN database on trunk interface, and the VTP clients will synchronize their VLAN database to it.

VTP servers also function as VTP clients.

Therefore, a VTP server will synchronize to another VTP server with a higher revision number.

Clients

Cannot add/modify/delete VLANs.

Do not store the VLAN database in NVRAM. (in VTPv3, they do).

Will synchronize their VLAN database to the server with the highest revision number in their VTP domain.

Will advertise their VLAN database, and forward VTP advertisements to other clients over their trunk ports.

Notes

If a switch with no VTP domain (domain NULL) receives a VTP advertisement with a VTP domain name, it will automatically join that VTP domain.

If a switch receives a VTP advertisement in the same VTP domain with a higher revision number, it will update it's VLAN database to match.

One danger of VTP:

• If you connect an old switch with a higher revision number to your network (and the VTP domain name matches), all switches in the domain will sync their VLAN database to that switch.

Transparent

Does not participate in the VTP domain (does not sync its VLAN database).

Maintains its own VLAN database in NVRAM. It can add/modify/delete VLANs, but they won't be advertised to other switches.

Will forward VTP advertisements that are in the same domain as it.

Changing the VTP domain to an unused domain will reset the revision number to 0.

Changing the VTP mode to transparent will also reset the revision number to 0.

VTP V2 is not much different than VTP V1. The major difference is that VTP V2 introduces support for Token Ring VLANs. If you use Token Ring VLANs, you must enable VTP V2. Otherwise, there is no reason to use VTP V2.