what is the purpose of the vlan.dat file on a catalyst 3750?

[craig5571]

Hi,

I would like to know the purpose of the vlan.dat file on a catalyst 3750? the reason I am asking this question is because, I used Ciscoworks lms 2.5 to upgrade a catalyst 3750's IOS. and after the upgrade the switch couldn't be pinged. the IOS upgrade worked perfectly otherwise. What I found out was that the vtp domain statement wasn't in the config and when I added it to the config, everything started working. I looked at a copy of the config before the upgrade and the vtp statement wasn't there. before the upgrade I completely erased the flash on the 3750 ( I did this because ciscoworks gets an error if it doesn't find the IOS in the root directory). What I'm thinking is, I erased the vlan.dat file. and since the VTP domain statement wasn't there and the vlan.dat file wasn't there , thats why I couldn't ping it.

So my question is this, what is the function of the vlan.dat file on a catalyst 3750?

Is there a similar file on a set based switch? ( I know the 3750 is IOS based)

Am I correct in thinking that the VTP domain statement just lets you get the VLAN.dat file and once you have that file on your flash. that the switch will function properly even without the vtp domain statement in the config

thanks

[amit-singh]

Hi,

Vlan.dat file is the file which have your Vlan database. The Vlans defined on the switch locally or via VTP server gets to the vlan database. I dont think this is the problem with the vlan.dat file.

I think what would have happened is that you completely erased the flash and the config.text file also got erased which contains the config of the switch.You did the IOS upgrade and reloaded the switch without saving the changes and you were unable to ping the switch as the config got erased. You again loaded the config on the switch and it got all the necessary info back and was reachable.

On the set based switch the file resides on the nvram and you will not be able to read the contents of nvram.

Let me know if it happened in teh same way or not.

regards,

-amit singh

[craig5571]

Amit,

Yes I did completely erase the flash, but ciscoworks backed up the running config as it was and used that. After the upgrade, the config was still there, I didn't put it back,(which means ciscoworks restored it and didn't use a blank config) the only thing I added was the vtp domain statement. and that statement wasn't in the original config.

I'm just wondering how the switch was working before without the VTP domain statement. I'm looking at the config before the upgrade and the VTP domain statement isn't in the config as it was before the upgrade, but I know for a fact it had all the vlan information and was working fine.

can a vlan.dat file be copied from one switch to another switch, or is the file specific to a certain switch? for example if someone move the vlan.dat file from a different switch but same VTP domain.

[amit-singh]

Craig,

Did you check the port assignment of the host from which you were trying to ping the switch. Let me know on which Vlan your PC was and which IP you were pinging before making the changes to the VTP domain name.

I think you can copy the Vlan.dat from one switch to another but I havenot tried myself practically.

regards,

-amit singh

[craig5571]

I tried pinging while I was logged into the console port of the switch, and I couldn't even ping anything on my own subnet. then someone pointed out that the vtp domain statement was missing and they added it. and POOF, everything was working.

when I was trying to ping it from my desk ( the switch is only 2 cubicles over) I was in a different vlan than the switch was in.

the switch was connected to the rest of the network through fa2/0/1. it was trunking with dot1q,

Just wanted to mention, this wasn't a production switch, it was just being used for testing at the time. (IOS deployment from ciscoworks LMS 2.5)

[glen.grant]

This is the correct behavior , if you are trunking then the vtp domain names must match on both ends in order for the trunk to work . We have seen this even in transparent mode on the 4506's and 2950's that we use . Also cisco recomends just using the command line now to populate the vlan database . Certain commands like the vtp domain name and such then get populated into the database . Unless you specifically delete the vlan.dat file the info in there should not change unless you make specific changes to it . If you indeed erase the vlan.dat file then your vtp domain names would not match and the trunk would not form .

[Kevin Dorrell]

I don't know about the 3750, but I have noticed some behaviour recently on a 4500. I know the acrhitectures are different, but I wonder ...

It used to be that default VTP mode was server, and the domain name was blank. But when you plugged a completely new switch into a network, it would latch onto the first VTP advertisment it saw, and made that the domain name. So it would join the domain seamlessly.

But I saw some different behaviour recently with a very recent IOS: instead, it defaulted to VTP transparent mode, again with a blank domain name. And it did not join the domain of its own accord.

I wonder whether you were observing something similar?

Kevin Dorrell

Luxembourg

[ankurbhasin]

Hi Criag,

What Amit is saying could be a possibility but what I think as you updated in you notes that as you added the VTP domain everything started wokring fine. This could be related to VTP related problem. Does your switch earlier working as client or server?

As once you added VTP domain name it might have updated itself with the VTP information from the VTP server in your network and got the vtp.dat file again and have started working.

You are very right saying that if you do not have a domain name it will not receive any updates from the vtp server and will not update vtp.dat file. Once u add the vtp domain name it will get an update from any server with higher revision number in your lan network.

Have a look at this link

http://www.cisco.com/univercd/cc/td/doc/product/lan/cat3750/12119ea1/3750scg/swvtp.htm#1221622

HTH

Ankur

[rakbar]

Craig,

As was stated in other emails the Vlan.dat file contains the your vlan information if you're in VTP client or Server mode. Dependng on the IOS the switch will normally boot with a VTP mode Transparent so you won't have an issue of unintentionally overwriting your VLAN database. The 3750 has a different directory structure. use dir all from a command line and check it out. If you're IP was associated with a vlan as opposed to a "routed port" (no switchport) you most likely lost the IP becuase the vlan.dat file may have been cleared. Just a thought. Good luck.

[craig5571]

I'm not sure which VTP mode the switch was in before the upgrade. It's in client after the upgrade, and before i'm pretty sure it was client, I know it wasn't server.

On our 3750 switches we dont use the routing features or HTTP, we use it strictly as a layer 2 switch with SSH capabilities.

Here is a part of the log from ciscoworks that details what IOS I had before the upgrade and after the upgrade.

Current SYSTEM SW : 12.1(19)EA1d ( File Name : c3750-i5-mz.121-19.EA1d/c3750-i5-mz.121-19.EA1d.bin )

Upgrading SYSTEM SW : 12.2(25)SEB2 ( File Name : c3750-ipbasek9-tar.122-25.SEB2.tar )

Flash Target: flash:c3750-ipbasek9-tar.122-25.SEB2.tar

Flash will be erased before loading new image

[amit-singh]

Hi,

Kevin, what you are saying is absolutely correct about the VTP domain name and VTP updation. I plugged a brand new switch a few days back with a diffrent VTP domian name and it updated itself with the VTP informationm running on my N/W. I was reading a doscument few days back and it says the samething about lugging a new switch in the n/w.

Craig,the problem was that your Vlan.dat file got deleted and all the ports fall back on Vlan 1. Your config still had the ports assigned statically to the differnt vlans. So when you pinged the switch it was not pinging as the ports fallback on the default vlan.The moment you changed the VTP domain name it got all the Vlan info back and it worked after that. I had the same problem few days back and I saw that all the ports were amber at that point of time. I updated the VTP info and it came back fine.

HTH,

-amit singh

[rseiler]

A slight correction, none of the ports actually change vlan membership, the IOS config (config.txt) doesn't change. The state you will be left in without a vlan.dat is:

1) the switch will boot and put all the ports in the configured VLANs per the IOS config

2) since the VLAN database is gone, there are no L2 VLANs except VLAN 1 available on the switch

3) since the VLAN that the port is configured doesn't exist, the port will not forward traffic

4) since the management interface (logical L3 VLAN interface) is probably other than VLAN 1, it will be in a down state since the L2 vlan doesn't exist in the database. This means that the switch will not be able to ping or perform any other layer 3 function because the management vlan logical interface is down

5) it is interesting to note that any ports in VLAN 1 will function fine, including trunks with a native vlan of VLAN 1 from a L2 perspective. Traffic will be forwarded across VLAN 1 if ports are in that vlan even if the management vlan is down

Hope that helps...

[minoc]

Hello all:

I have the same problem, after performing a password recovery on a 2950 switch all ports are amber and no vlan traffic is working.

When checking the VLANS, no vlans shows up, just the default ones. Using the show interface trunk command I see that the trunking is working correct. The switch is on client mode with the correct Domain name.

I tried to fix this by copying a vlan.dat file from another swict (Server) with tftp, it did not work.

Any ideas?.

Regards,

Carlos Roque

[amit-singh]

Hi Carlos,

If trunk is working fine on you switches, then try making a dummy Vlan on your VTP server and have the VTP information flow to this switch which is not having the Vlan info. Please check the VTP revision number also and see that should increase on your rest of the switches and this should get the same number .

HTH,

-amit singh

[minoc]

Hello,

I fixed the problem by setting the vtp password to null, changing the vtp mode to transparent and back to client.

Regards,

Carlos Roque