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Switch Failure

We recently had a power failure on one of our 4912 Core Switches. This has happened many times in the past, but this time we lost the VLAN information in this switch. Any ideas what would cause this too happen?

Hall of Fame Super Bronze

Re: Switch Failure

Vlan information is held on a file called vlan.dat stored in flash.

If this file becomes corrupted, the Vlan information will be lost. Same behavior can be seen with IOS file corruption.

Perhaps the file was being accessed during the power failure, causing the corruption.

Do you have a VTP Server/Client model ? Was this a VTP server or client ?

New Member

Re: Switch Failure

Thank You

The switch was setup with VTP Client. We do nott use VTP, so I made it transparent.

Hall of Fame Super Bronze

Re: Switch Failure

The switch was changed from VTP Client to VTP transparent ?

When the switch runs in VTP transparent, the Vlan information is stored in the running-configuration, did you verify this information was there before the power outage ?

Perhaps the configuration was there but not written to NVRAM. Any changes not saved to NVRAM, will be lost after a reload.

Cisco Employee

Re: Switch Failure


I believe this switch is working as VTP client and when it got reloaded it was not able to contact VTP server and thus there was a loss in vlan information.

If this is a VTP server then vlan information sould have got saved in nvram and had not lost the vlan configuration after reload until and unless as Edison pointed there can be a corruption in vlan.dat file which is a rare chance.

Please point some more inputs what is the scenarios and "sh vtp status" from the switch.




Re: Switch Failure

We have seen this more than once on all the cat4000 series devices like the 4000,2980,2948's. Don't know why this happens. Never have seen it on a catos 6500 box . We have seen it on a simple reload where we had upgraded the code but it loses some of the vlan info. For some reason the 4000 series seems to be susceptible to this.

New Member

Re: Switch Failure

On certain of the older stackables, the VLAN database is kept in just a plain text file on the flash filesystem.

Often, if you did a code upgrade the good old-fashioned way and erased the flash without writing mem and going into the VLAN db config from the exec level, you can lose all your VLAN information.

If you had made changes to the VLAN db and didn't write them, or to the config and did not write it, when the power goes out you can lose the data as well.

When the switch boots, if the VTP domain name and VTP mode in the startup-config and vlan.dat files do not match, the switch uses the configuration in the vlan.dat file.

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