Will trunked vlan remain up if vtp server fails?

[thessick]

We are trunking vlan 999 from a 6513 vtp server to a 6509. The 6509 is a vtp client and all ports are on vlan 999. If the 6513 vtp server is shut down, will the 999 network continue to function on the 6509?

Thanks

Tom

[glen.grant]

Are there any other vlans on the trunk ? I would think if you make sure the native vlan is 999 on both ends of the trunk it would stay up though the only reason the vtp server is going to go down is if the switch fails , there is no way to shut it down unless you switch the trunk mode to transparent .

[ankurbhasin]

Hi Tom,

Even if your VTP server is not available and your VTP client is up and running you are good to go means your vlan 999 will work on vtp clinet switch but take an instance if your VTP server is not available and bychance your vtp client switch gets rebooted you will loose all vlan config from vlan.dat file on vtp client and you will see only one vlan which is vlan 1 available on your vtp client switch.

HTH

Ankur

[milan.kulik · Accepted solution]

Hi Ankur,

this is a theoretical behaviour.

In real networks even some VTP clients (2900XLs, e.g.), save VLAN info received via VTP to vlan.dat file and keep it after reload (even if VTP server is not available). See "VTP bomb".

To the original question:

VLAN 999 should keep running even when the VTP server failed.

If your VTP client keeps the VLAN ifno saved (either in vlan.dat file or startup config), it should remain even after the VTP client reload.

But generally, it's recommended to configure more (2 at least) VTP servers in your network.

Regards,

Milan

[ankurbhasin]

Hi Milan,

I have tried it many a times in my lab with this scenario and vtp clienst happen to loss the vlan information after reload if VTP server is not available so I thaught y to take a risk. You are right it sis always better to have more than 1 VTP server.

Ankur

[milan.kulik]

Hi Ankur,

which HW have you tested in your lab?

I've just reloaded a C2924-XL running IOS 12.0(5)WC10 configured as a VTP client.

It's not connected anywhre, i.e. VTP server is not available.

But the VLAN info remains available, I can see several VLAN via sh VLAN.

There is also a vlan.dat file on the Flash containing the VLAN info.

VTP revision number is 65.

So definitely there are some switches existing which don't lose VLAN info after reboot even when configured as a VTP client and the VTP server is not available.

Regards,

Milan

[limtohsoon]

Hi all,

As far as I can recall, I have tried to reboot a Catalyst 6509 (hybrid model, i.e. CatOS on Sup, IOS on MSFC) which is a VTP client that had previously synched its VLAN database from a VTP server. The switch was rebooted with all trunk links to the production network removed. It actually lost all VLAN info except the reserved VLANs (i.e. VLAN1, 1002-1005, etc).

I will verify this again if I got the chance.

Thank you.

B.Rgds,

Lim TS

[milan.kulik]

Correct.

CatOS switches have no vlan.dat file on the Flash and don't save VLAN info into their config when configured as a VTP client.

Regards,

Milan