VLAN Trunking Protocol (VTP) Overview and Configuration

vtp topology

It’s time to take a look at VLAN trunking protocol ( VTP ). VTP is a protocol that provides VLAN configuration to spread to the whole network. Using the Layer – 2 frames, VTP provides us to change VLAN names, manage VLANs, adding or deletin VLANs etc.


vtp topology


First , all switches has a revision number of 0. When you add new VLANs revision number increases one. For example when you create VLAN 10 , revision number is 1 , when you create VLAN 20 too, revision number is 2 anymore. But what if we hard code a VTP revision number and plug that switch in the network ( As you can see in the figure , rev : 1302 ). Answer is that : All other switches change their VLAN databases according to the new switch.



VLAN information can be changed. ( You can add or remove VLANs )

Sends and receives VTP update.

Can save VLAN config.


VLAN information can’t be changed. ( You can’t add or remove VLANs )

Sends and receives VTP update

Can’t save VLAN config.


VTP updates are forwarded.VLAN information can be changed. ( You can add or remove VLANs )

VTP advertisement isn’t accepted.

Can save VLAN config.


*VTP pruning provides that unnecessary traffic is blocked over the trunk links.

*Works only with VTP server mode.


Normally if a client makes broadcast which is in switch 1 and green vlan, that traffic goes to switch 3 too even if there is no green vlan created on it. This is actually what pruning does ! Pruning avoids this to happen. ( VTP Pruning is not active defaultly )


1- VTP status is verified :

SWITCH_A#show vtp status
vtp version 2
config revision : 0 (There's no VLAN database or didn't receive any VTP updates)
Number of existing VLAN:5
VTP operationg mode : Server
VTP domain name : ( If you plug a new switch which has a domain name, this switch updates itselfs with that domain name and password. That's a dangerous situation. So if you don't use a port as a trunk, put it swiftly in the access mode ! )

2- VTP domain name is given.
SWITCH_A(conf)#VTP domain name APPLE( Please pay attention that domain name is case sensitive ! ); As soon as you do this, domain name of switch B and switch C turns to "APPLE".

Let’s verify something too…

SWITCH_A(conf)#VLAN 10(exit)
SWITCH_A(config)#VLAN 20(exit)
SWITCH_A(config)#VLAN 30(exit)
SWITCH_B(config)#VTP mode client
SWITCH_C(config)#VTP mode client

After creating those vlans let’s verify the config revision number of SWITCH_A

SWITCH_A#show vtp status
Config revision : 3 

(VLAN 10-20 and 30 are added to the other switches databases too because SWITCH_A is server , others are client)

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