VTP configuration

We’ve already learned that using VTP makes it is possible to make configuration changes on one or more switches and have those changes automatically advertised to all the other switches in the same VTP domain. In a typical network some switches are configured as VTP servers and other switches are configured as VTP clients. A VLAN created on a VTP server switch is automatically advertised to all switches inside the same VTP domain.

NOTE
With VTP V1 and V2 it is not possible to completely disable VTP on Cisco switches; the best you can do is to place the switch in the VTP transparent mode. VTP V3 adds the mode off option which effectively disables VTP. This article describes the configuration of VTP V1 or V2.

To exchange VTP messages, five requirements must be met:

1. a switch has to be configured as either a VTP server or VTP client
2. the VTP domain name has to be the same on both switches
3. if present, the VTP domain password has to be the same
4. VTP versions have to match
5. the link between the switches has to be a trunk link

Consider the following example network:

VTP configuration example

We have a network of three switches connected via trunk links. On SW1, we will configure the VTP domain name using the vtp domain NAME command and VTP password using the vtp password PASSWORD commands:

Configure VTP domain and password

NOTE
The default VTP mode on Cisco switches is the server mode, so the command vtp mode server wasn’t necessary in the SW1 configuration pictured above.Now we need to configure SW2 and SW3 as VTP clients. We can do it using the following set of commands:Configure VTP clientVTP client configuration

Now, when we create a new VLAN on SW1, the VTP will be sent to SW2 and SW3 and the new VLAN will be created automatically on SW2 and SW3:

VTP updates

On SW1, we will create a new VLAN:Create new VLAN

SW2 and SW3 will create the VLAN 30 automatically. We can use the show vlan command on both switches to verify this:

SW2:

New VLAN created

SW3:

New VLAN created

To display the VTP configuration information, we can use the show vtp status command:

show vtp status command

The most important field listed in the output above is the Configuration Revision number.  This number indicates the level of revision for a VTP packet. Each device tracks the VTP configuration revision number that is assigned to it. This information is used in order to determine whether the received information is more recent than the current version.

Each time you make a VLAN change on a VTP server, the configuration revision number is incremented by one and a VTP advertisement is sent. The switch that receives a VTP packet compares the configuration revision to its own revision. If the configuration revision number in the received VTP advertisement is higher than its own revision number, the switch will overwrite its VLAN configurations with the new information that is being advertised.

NOTE
It is important to check a new switch’s VTP configuration revision number before adding it to your network. If the revision number on the new switch is higher than the current revision number of other switches on the network, all current VLANs could be deleted!

Prerequisites for 200-301

200-301 is a single exam, consisting of about 120 questions. It covers a wide range of topics, such as routing and switching, security, wireless networking, and even some programming concepts. As with other Cisco certifications, you can take it at any of the Pearson VUE certification centers.

The recommended training program that can be taken at a Cisco academy is called Implementing and Administering Cisco Solutions (CCNA). The successful completion of a training course will get you a training badge.

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