Introduction to VTP (VLAN Trunking Protocol)

VLAN Trunk Protocol (VTP) reduces administration in a switched network. When you configure a new VLAN on one VTP server, the VLAN is distributed through all switches in the domain. This reduces the need to configure the same VLAN everywhere. VTP is a Cisco-proprietary protocol that is available on most of the Cisco Catalyst series products.

VTP Modes

You can configure a switch to operate in any one of these VTP modes:

Server—In VTP server mode, you can create, modify, and delete VLANs and specify other configuration parameters, such as VTP version and VTP pruning, for the entire VTP domain. VTP servers advertise their VLAN configuration to other switches in the same VTP domain and synchronize their VLAN configuration with other switches based on advertisements received over trunk links. VTP server is the default mode.

Client—VTP clients behave the same way as VTP servers, but you cannot create, change, or delete VLANs on a VTP client.

Transparent—VTP transparent switches do not participate in VTP. A VTP transparent switch does not advertise its VLAN configuration and does not synchronize its VLAN configuration based on received advertisements, but transparent switches do forward VTP advertisements that they receive out their trunk ports in VTP Version 2.

Off (configurable only in CatOS switches)—In the three described modes, VTP advertisements are received and transmitted as soon as the switch enters the management domain state. In the VTP off mode, switches behave the same as in VTP transparent mode with the exception that VTP advertisements are not forwarded.

VTP Configuration Guidelines

  • VTP defaults for the Cisco Catalyst switch:
  • VTP domain name: None
  • VTP mode: Server mode
  • VTP pruning: Enabled or disabled (model specific)
  • VTP password: Null
  • VTP version: Version 2
1. A new switch can automatically become part of a domain once it receives an advertisement from a server
2. A VTP client can overwrite a VTP server database if the client has a higher revision number

3. A domain name cannot be removed after it is assigned; it can only be reassigned

Important! When you connect new switch to the network make sure that his revision number is set 0. if the new switch revision number is greater than the server revision number all the VTP clients switch will update their VLAN database from the new switch. it can cause a wipe of all your VLANs in your network!

Client Configuration Revision
Server configuration Revision

So how can I reset the new switch revision number to zero?

it’s easy just change the VTP MODE in the new switch from server to a transpernt mode and back to client mode.

What is VTP Pruning?

  • VTP pruning is disabled by default in Cisco switches. VTP pruning helps to send broadcasts only to those trunk links that actually needs the information. For example, if switch A does not have a port configured for VLAN 7, and broadcast is sent throughout VLAN 7, that broadcast or traffic will not pass through the trunk link to switch A

Configure VTP

Author: Meni T.

IT Infrastructure Manager

3 thoughts on “Introduction to VTP (VLAN Trunking Protocol)”

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