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VTP is a layer 2 protocol that allows to control, create and delete VLANs from a central vtp server. Cisco swithes are in “vtp server mode” by default. In a large network there can be mant swithes and configuring this swithes can be very difficult one by one for VLANs. So VTP help us to configure VLANs in one vtp server and then generate this information to other swithes.

There are three vtp modes:

  • Server Mode
  • Client Mode
  • Transparent Mode


As I mentioned before, VTP Server mode is the default mode for the swithes. You can create, delete and modify VLANs on this mode. VTP Client mode is the passive VTP mode that waits for VLAN information from VTP Server. On this mode you can not make any creation, deletion and modification on VLANs. And the VTP Transparent mode is a special mode that it only creates,deletes and modifies its own VLANs and never change its VLANs by other VTP information coming from VTP Servers. To summarize they do not synchronized. But they can forward VTP information that they get from VTP Server. To configure VTP mode use “vtp mode mode”command.

For VTP information, related swithes must be in the same “VTP domain” with the VTP Server. To configure VTP domain use, “vtp domain domainname” command. It is not necessary but if used, “VTP Passwords” must be the same too. You can configure this by “vtp password password” command

Beside these parameters there is another important parameter called “configuration revision number”. This number is increased after an update on VLANs. The swithes has the bigger number configuration revision number has the latest VLAN information. And so if there are more than one VTP Server, then the most recent one will be change the other one. For this reason me must be very carefull while ading new swithes to the network. If the newly-added switch’s VTP Mode is Server and it has the same required parameters with the VTP server, then there can be a big problem.This can cause all our VLANs deleted.

To check VTP information of a switch, “show vtp status” command will help uslike below:

VTP packets sent over trunk ports on management VLAN VLAN 1. This synchronize the other swithes and saves the VLAN information to tthe NVRAM.So these vLAN information do not go away after reboot.

There are three VTP versions; VTP version 1, VTP version 2 and VTP version 3. Generally used one is VTP version 2. And the VTP version 3 is a new one. The difference of these versions will be explained in another article.You can configure version by “vtp version version” command.

VTP packets are sent every 5 seconds or after a VLAN information change occurs.

One more point is “VTP prunning”. If VTP prunning active in a VTP domain, then if this switch has not any active port on a specific VLAN, the traffic will not go on this specific VLAN. By doing this, unused VLANs do not pass traffic and bandwidth increases. To configure VTP prunning, this must be enabled on all the switches in the VTP domain.By default it is disabled and to enable VTP prunning use “vtp prunning enable”.

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About the Author
Gokhan Kosem is a telecommunation and network engineer. His ambition to IP networks and end-to-end system installation made him to prepare this web-site. By sharing his experiences about various networking protocols beside different system installation experiences and Cisco, Juniper, Alcatel-Lucent devices configurations, he is aimed to be helpful for his collegues in all over the world. He is currently lives in Istanbul, Turkey.

One comment for “VTP (VLAN Trunking Protocol)”

1
Mohamed Rafi

Hello Sir
Mohamed Rafi
I am an IT Engineer, experienced more than five years. I have done different types of network switch specially Cisco. In cisco there possible to use the coding for VTP domain but for Alcatel, You can assist me the coding for the VTP.
I am having Alcatel SRS 6850E-U24X as core switch 1 no. and OS 6450-24 as edge switches 12 nos.
What is the coding for VTP.

Thanks

September 1st, 2014 at 19:36

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