VTP in brief

VTP is a Cisco proprietary protocol used in switching environment to reduce the administrative overhead of managing VLANs configuration.Lets explore how VTP can reduce VLAN management tasks by the following example:

Assuming that you have o­nly three switches in your network and you need to configure 3 VLANs with each switch is having members in each VLAN

without VTP: you need to configure the three VLANs with all parameters o­n each of the three switches.(i.e. tripling the configuration tasks)

with VTP: you need to configure all VLANs with all parameters o­nly o­nce o­n o­ne of the switches and all these information will be propagated throughout the domain.

VTP operation logic:

1- VTP mode must be configured o­n each switch to be o­ne of the following.

• Server – In this mode you can add, delete and modify VLANs. You can also set other configuration options.
• Client – you cannot create, change, or delete VLANs o­n the local device. Switches in this mode will sychronize its VLAN configuration based o­n received messages.
• Transparent – A VTP transparent switch will not advertise its VLAN configuration and does not synchronize its VLAN configuration based o­n received messages. VLANS can be created, changed or deleted when in transparent mode. In VTP version 2, transparent switches do forward VTP messages that they receive out their trunk ports.

vtp mode [server | client | transparent] is used in the global configuration mode to set the VTP mode.

2- VTP domain must match o­n all switches participating in the same domain. The switch will o­nly accept advertisement messages from the same domain.

vtp domain [name] is used to set the VTP domain o­n the switch.

3- VTP password must match o­n all switches in the same domain if authentication is used.

vtp password [password] is used to enable password authentication in the VTP domain.

4- VTP messages propagate o­nly over trunk links, so at least o­ne trunk must be up between two switches.

5- Start making all creation, modification and deletion of VLANs o­n o­ne of the siwtches in the server mode.

Known issues:

• VTP version must match within the same domain.
• Revision number must be reset or at least make sure it is lower the the current revision number in the domain before inserting a new switch.

Check out this link for a flash animation explaining VTP concepts in more details VTP flash animation.

More o­n VTP configuration to come in the How-to section.