VTP clarifications

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Aug 15th, 2007
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hi guys,

i want to clarify these. Based on the cisco flash site on vtp, when u reboot a vtp client it will loose all the vlan info and the rev. # is set to zero. But i tried it out on our laboratory and doesnt work, i tried rebooting the client on a separate network but still has the vlan info.


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purohit_810 Wed, 08/15/2007 - 19:09
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Is your Switch is in Server mode or client mode?

Switch by default comes with Server mode.

If it is in server it will store configuration VTP into its' CONFIG.TXT file otherwise it will not.


Dharmesh Purohit

jeffbriones Wed, 08/15/2007 - 19:11
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The switch is in VTP client mode. I tried rebooting it and all the info i got from the VTP server is still on it. The site specified that the vlan info will not stay on the nvram thats why after reboot all the vlan info are erased.

guruprasadr Wed, 08/15/2007 - 21:25
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In an VTP Environment all VLANs, VTP Information will be stored only in the NVRAM of Switch operating in SERVER Mode.

Whereas the Switches in Client Mode will receive the VTP Information based on Revision Numbers after adding in the VTP Domain.


Best Regards,

Guru Prasad R

Edison Ortiz Thu, 08/16/2007 - 04:17
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Very interesting. What type of switch are we dealing with ? IOS Version ?

Can you please post the output from

show vtp status


show vlan ?


kristofspriet Thu, 08/16/2007 - 04:35
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If you go the the vlan database. And do a show vlan when your switch is not connected to the vtp server and the vlans are still there. Then the vlans must have been created manualy and you should delete them in de vlan database.

tromer Thu, 08/16/2007 - 10:07
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So your client isn't still connected to the VTP server? I was thinking it was re-adding the vlans on the reboot if it could still talk to the server...

ilya.varlashkin Thu, 08/16/2007 - 11:00
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Even in client mode switch writes vlan.dat file, which is preserved across reboots. It's because of this fact one should be careful about revision even when bring VTP-client to new network. Regardless of mode higher revision wins, so you can wipe out VLAN data of your production network even from client.

When you disconnect switch from the network it continues to use vlan.dat:

XS4>sh vlan summ

Number of existing VLANs : 40

Number of existing VTP VLANs : 40

Number of existing extended VLANs : 0

XS4>sh vtp status | i ode

VTP Operating Mode : Client

VTP Pruning Mode : Disabled

VTP V2 Mode : Enabled

XS4>sh vlan summ

Number of existing VLANs : 40

Number of existing VTP VLANs : 40

Number of existing extended VLANs : 0

XS4>sh ver | i time

XS4 uptime is 2 minutes

XS4>sh vtp counters

VTP statistics:

Summary advertisements received : 0

Subset advertisements received : 0

Request advertisements received : 0


So after reboot your swicth also has vlan info from vlan.dat.


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