Switching – VTP

Hello dear readers,
In the past article we’ve talked about the role and functionality of VLANs and network trunks. In today’s post we will talk about a feature that was invented in order to make VLAN administration much easier, VTP (VLAN Trunking Protocol). If you are a network Administrator in a mid to large network, you will probably encounter a lot of VLAN problems. Usually, big companies have a lot of configured VLANs and they tend to change them frequently. Imagine what would happen if you’d have to configure 100 switches with 30 VLANs each, the process would take a very long time. VTP is a a protocol that allows switches to propagate VLAN information throughout the network. The mechanism of VTP is quite simple, a VTP server switch is configured by Administrators and any VLAN information configured here is automatically sent to all VTP-enabled switches in the network. Other switches except the VTP server are configured as clients and they are the ones that receive VLAN information from the server. Every VLAN change (creation, modification, deletion) is notified by the VTP server. The benefits of using VTP are visible from the start: you configure VLANs from a single point of administration, VLAN information is automatically propagated without the Administrator’s intervention, makes VLAN monitoring easier and all switches share the same VLAN information.
Before showing you how to configure VTP on a Cisco switch, I want to explain the main elements of the VLAN Trunking Protocol:
There are three VTP Modes:
VTP Domain: this element describes the network devices that are part of the same VLAN configuration. All switches configured with the same VTP domain will share the same VLAN information.
VTP Client: a switch that is configured to receive the VTP server’s VLAN information. A VTP client will not be able to modify any VLAN configuration.
VTP Transparent: a switch that will receive and forward VLAN information but it will not participate in the VTP operation. Any VLAN configuration made on a VTP Transparent switch will not be propagated to other network devices.
VTP Messages: information exchanged between switches.
VTP Pruning: mechanism for controlling VTP traffic.
There are some steps that you need to take in order to configure VTP in a network. When you first configure a Cisco switch, it will be automatically selected as a server switch if no other server is configured as so. To verify the VTP mode of a switch , type show vtp status from the privilege exec mode:

show vtp status
In this image you can see the VTP version (here is 2), the revision number which is an item that counts the number of VTP changes that have been made in the network, the VTP operating mode which in this case is Server. The domain name is not configured yet, but we will do that in a minute.
   To configure VTP on a Cisco switch, you will have to take the following steps:
  First, enter the global configuration mode and type in, vtp ? to see the available commands:
vlan trunking protocol
   We must then configure the VTP domain as follows:
vtp domain
In this example, I’ve configured the VTP domain with the network name. All devices that are part of the same network must use the same VTP domain name. Next, we will configure the VTP mode from the following modes: server, client or transparent. We’ve talked about the earlier:
vtp domain
I’ve configured the switch to be in the SERVER mode, all other switches in the network must be either in the client or in the transparent mode. I will select the VTP version to be 2 by typing vtp version 2:
vtp version
In the end I will set the VTP password using the vtp password [string] command:
vtp password
To verify your VTP configuration, type show vtp status:
vtp status
You can now see that all features have been changed according to our configuration commands. A client from this network would be configured using the following commands:
vtp domain network / vtp mode client / vtp version 2 and vtp password admin
vtp configuration
   These are all the commands that you need to configure on a Cisco switch in order to enable VTP. As you can see, it is pretty simple to enable this cool feature on a networking device. Remember that any VLAN configured on the VTP-server switch, will be propagated to all VTP-client or VTP-transparent enabled switches. I will post a video tutorial in a future article in which you will better understand how to configure VTP on Cisco devices.
  I hope you will enjoy this article, stay tuned for more to come. Comment and share this post and enjoy a wonderful day.

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