VTP vlan.dat question

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With my TestOut LabSim CCNA training software, in one video the trainer says that vlan.dat is stored in NVRAM only on the VTP Server but not with the VTP Client.

Cisco ICND2 Exam guide says that vlan.dat is stored in Flash on both the VTP Server and Client. Why the inconsistency, has something changed? who is right, the book or my video training? Ok, I know this will not be a big thing for my ICND2 exam (Aug 26) but I would still like to have consistency in my understanding of things.

Thanks,
Nick.

 

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According to Cisco themselves:

 

Thanks for the update. This must be new? my ICND2 book (Wendell) bangs on about vlan.dat and Flash memory( Sever and Client). The Cisco text you've pasted does not even mention vlan.dat or Flash.

Nick.

 

I don't think that's a new thing. The 3750 is a new switch... but the ICND2 is a new book as well. As far as which source is correct... as good as Wendell Odom is, I'd trust Cisco's own site. Perhaps he meant to say NVRAM and thought/typed "Flash". That sort of thing happens all the time to us writers - more often than we'd like.

Besides... Flash is used to store IOS images. You can also store a backup copy of your config there.

I'm guessing that vlan.dat is where that VLAN info is stored.

 

OK, thanks again. I'll go with Cisco on this as well.

Nick.

 

Just found the following info in the "ICND2 Third Edition Steve McQuerry" book:

"...VTP clients that run Cisco Catalyst operating systems do not save the VLANs to NVRAM.
When the switch is reloaded, the VLANs are not retained, and the revision number is zero.
However, Cisco IOS VTP clients save VLANs to the vlan.dat file in flash memory, retaining
the VLAN table and revision number..."

Perhaps that explains it?
Nick.

 

But why would a VTP client retain information that can't even be configured on it? Why not just hold it in RAM, and resynch at reboot? This is how I've always thought it works, but I could be wrong.

If it IS necessary... then why doesn't the VTP client just save it in NVRAM like VTP servers do? Makes no sense to me...

 

well there is a command which adds something interesting to the topic

delete flash:vlan.dat

that i have seen in lots 3 of training materials, and have been instructed that all information re vlan's will still be kept even if you erase the configs, but dont erase this file.

Just googled this command and more info

http://www.mcmcse.com/cisco/guides/vlandat.shtml

and http://www.thebryantadvantage.com/C...ng Configurations On Routers And Switches.htm

Although both sites are pretty similar

Now id imagine, that because with VTP any changes that are made on a VTP server it has to increment the revision number of the Vlan database and then send an update to the VTP clients and servers to notify.
The update then occurs in a way that sounds like a file being transferred, According to Jeremy Ciora it "first flushes the Vlan info", and then transfers the new vlan information over a trunk, it would make sense for it to be in the form of a file (as i doubt it could execute commands on a different switch).

 

Doesn't make sense at all... it's no different than routing information is transferred: as data. And if it made sense to transfer it in the form of a file... why isn't it stored similarly (as a file) on VTP servers?

Why don't you create a VTP server and VTP client and see if the file appears in your Flash?

 

My understanding is that VTP servers and clients both store the data in vlan.dat

The exception is a switch in transparent mode, which stores the vlan info in the running config

When I cleaned down my lab, there was a VLAN.dat file on the VTP clients that I had to delete

 

You can believe your understanding, or you can believe Cisco's Web site. You might be right... then again, I haven't often seen them wrong. Just sayin'.

One thing you might consider is this: changing a switch from VTP client mode to VTP server mode might not delete the vlan.dat file from flash... making you mistakenly believe that a VTP server stores the information there as well.