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New Member

VTP question

guys just a quick one regarding VTP....onloy server generate vtp advertisments so if i have a swicth which is in transparent mode.....and has a higher revision no and i attached that switch to exsisting network...will it overwrites the vlans as it has higher version......seconly when client reseacive vtp adv it doesnt update vlan.dat or nvram but transparent what is the purpose of that....why we use client and transparent can someone explain plz.....thirdly there can be more then one vtp server in the environment what is the use of having two VTP servers??? guys just wanted to get my head around regaridng VTP?????? like i m very confuse that when transparent brige recieve vtp adv it saves in its vlan.dat but doesnt upodate while client do the opposite thing what is the point of saving somehting but not updating....thanks

Cisco Employee

Re: VTP question

Hi Buddy,

If the switch is in transparent mode it will not generate the advertisements and will not update the vlan.dat even if it has higher revision number. The switch which is either a vtp client or a vtp server with higher revision number will update the vlan.dat on other switches.

When client receives a vlan.dat it always updates in vlan database. The purpose of VTP client mode is to have the switches only to accept the vlan database without modiying/creation or deletion capabilities.

The purpose of transparent mode is to silently relay the vlan database to the other client switches without updating its own database. For example

Switch A,B and C are trunked to each other. Switch A is Server and has few user vlans for marketing and sales. Switch C is the client and needs the same vlans. The connecitivity is like Switch A---> Switch C---> Switch B. Switch B belongs to Engineering department and needs its own set of vlan. In this case Switch B will be configured as transparent switch and it will relay the Vlan database info from Switch A to C.

The purpose of two VTP servers is for the redundancy and in case if one switch goes out the other backs it up and we wont have any vlan database overwriting or corruption issues over the network.


-amit singh

New Member

Re: VTP question

Hi amit

thanks for your reply but i guess onr correction....even in client mode the switch doesnt generate vtp adv i just saw it in ccie book by odel and narren mehta....according to the book transparent update its valn.dat but pass it on while client doesnt store or update vlan.dat??? i m seriusly confuse

Re: VTP question


yes the client can even update the revision number of server if it is having old info.

in transparent the update recieved from any switch wether a server or client are forwarded but they are not utilized to update their local info.



New Member

Re: VTP question

Thanks amit for the valuable information, so basically if a switch is added to existing domain (client or server mode)with > config rev number than the vlan information (vlan.dat file) will override existing configurations.

I am correct in assuming that to resolve this problam then I can take the switch out of the domain , then on a switch running (server mode) reapply the vlan information

switchport trunk encap dot1q

switchport mode trunk

switchport trunk allowed vlans (put vlans here)

Then I can go to the other switch and reapply to domain with updated configuration revision number to where all switches in the test domain have config rev #10 for example. Thanks and have a great day

Re: VTP question

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