VLAN Trunking Protocol allows switches to share VLAN information dynamically. This way an administrator only needs to change VLAN information on one switch and it will automatically propagate to other switches in the VTP domain. This does not replace the need to assign specific switchports to specific VLANs, but it does reduce the administrative time it would take to configure VLAN changes on all switches in a large network. {loadposition adposition5}In order to implement VTP you need to know how the protocol operates and functions and how to configure it. For VTP to begin functioning the participating switches must be configured with the same VTP domain name. A VTP domain can support only 255 VLANs. Switches running VTP can be configured for three different modes: server, client, and transparent. A switch with VTP enabled is in server mode by default. VTP advertisements are sent every 5 minutes by default, or when there is a change in configuration revision number caused by the addition or deletion of a VLAN on a server.

VTP Modes

Server Mode – In VTP server mode you can create, modify and delete vlans. VLAN information is synchronized with other VTP servers and clients on the VTP domain. You can have multiple VTP servers in the VTP domain and VLAN information is synchronized according to the server with the highest configuration revision number. VLAN information is stored in the the vlan.dat file in NVRAM/Flash memory.

Client Mode – Switches in VTP client mode receive and synchronize VLAN database information from other VTP servers and VTP clients in the VTP domain. A VTP client can update a VTP server if it has a higher configuration revision number. VLAN information is stored in the “Running-Config” or DRAM. If a switch in client mode is restarted then all VLAN information, including the VTP revision number on the switch is lost and must be relearned from the VTP server once the client has restarted.

Transparent Mode – Switches in transparent mode receive updates from other servers and clients but do not participate in the VTP Domain, rather they allow the VTP updates and advertisements, to pass through the switch on to other switches in the VTP domain. Transparent mode switches do not synchronize their VLAN information with other VTP servers and clients, but maintain their own separate VLAN configurations.

Video Tutorial

In this video tutorial, I demonstrate how VTP shares VLAN information by configuring a VTP server and a VTP client, and then connecting them together with a trunk. The demonstration is easy to follow along with, in Packet Tracer. Here are the starter files for Parts 2 and 3: VTP2-begin.zipVTP3-begin.zip

In this tutorial, I cover setting up switches as a VTP server and a VTP client

 In this tutorial, I cover setting up a switch in VTP transparent mode

In this tutorial, I demonstrate how a VTP client can actually change a VTP server if the client has the higher revision number

Author: Dan

Dan teaches computer networking and security classes at Central Oregon Community College.

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