VTP Vlan question

[Yannick Vranckx]

Dear,

This question has been bugging my mind lately, say you configure a switch to put it inside a VTP domain. Let's say the access vlan has to be 8 and voice 10.

If you preconfigure the ports the switch will auto create the vlan locally to the switch, but when you put in a VTP domain as a client, will it overrride the VLAN's you created.

Since if you already made the ports a member of vlan 8, and vlan 8 also exists in the VTP domain you will insert the switch in, will it just override your switch settings?

Kr,

[Joseph W. Doherty]

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Posting

I believe VTP won't override the actual port VLAN setting, but it should override the switch's previously defined VLANs.

In your example, the ports in VLAN 8 would still be in VLAN 8 as it's also defined to the VTP domain, but suppose VLAN 8 wasn't.  In that case, your VLAN 8 ports wouldn't extend across any trunks, and they might no longer function as a VLAN within the switch itself.

[devils_advocate]

As soon as you put your switch in VTP Client mode, it will overwrite the previously created Vlans with the ones from the VTP Server.

If ports on the switch are already in those Vlans, they will remain there.

It will not cause the switch any issues unless the VTP server does not have a Vlan which the Client switch has ports that are a member of.

[paul driver]

Hello

Just to be clear - A VTP client CAN overwrite a VTP server if the revision number is higher then that of the current VTP server

The best to make sure such a thing doesn't happen it to change the vtp mode to transparent and back to client before connecting up as this will reset the revision number to a zero value - Unless you network using vtp ver 3 that is?


res

Paul

 

[Yannick Vranckx]

Paul,

Thanks this is some valuable information, i knew there was something i had to take care of. The staging switches come straight out of the box. But i knew in the back of my head there was something with that.

Got it quite clear, i can prepare a switch with putting ports already in access vlan's and voice vlans, but it to transparent mode. When plugging into the network i check the revision is set to 0 and safely make it a client and the VTP will override my local vlan's, since i'll be matching the access vlans that are already existent in the VTP.

[paul driver]

Hello

Yes and as other have stated, the "new" switch will receive all the other vlans already created in the vtp domain this "new" switch is to be  attached too.

(note for a new switch:
I guess the revision will be low any way as to not override the current vtp domain but its worth while getting into the habit of changing the vtp mode to transparent back to client before connecting it to the network

note for a old relocated switch:
you have the option also to delete the config.text and  vlan.dat file in the flash and reboot the switch, this will delete the exiting config of the switch and its vlan database and after reload it will come back to a default configuration (vtp database included)

Lastly if your using vtp ver3, The inbuilt security of this version negates the possibility of overriding the vtp database

res

Paul