Deleting the VLAN Database from a Cisco Switch (IOS or Nexus)

If you have your own Cisco switch equipment at your home lab or at your work environment you might have encountered the situation that you want to completely erase the whole switch configuration including any VLANs that are already configured on the switch (usually the vlan.dat file).

On a Cisco switch, erasing the switch startup configuration is one thing and erasing the VLANs that exist on the switch is another thing.

The VLAN information is stored in a file with name “vlan.dat” which exists in the flash storage of the switch. If you run “show flash” command you will see this file. This is also called the VLAN Database.

It is a good practice to completely erase everything on a switch (both switch configuration and switch Vlans) before using the switch in another part of your network. This is important in order to avoid any network conflicts because of any old configuration settings that are already configured on the switch.

Now let us see how to delete the configuration and Vlans from a Cisco switch.

Regular Cisco IOS Switches

1) Deleting the switch configuration

This is the easy part. It’s the same as deleting the configuration from any other Cisco network IOS device. Basically you need to delete the “startup-configuration” and then reboot the switch.

Switch#erase startup-config

Erasing the nvram filesystem will remove all configuration files! Continue?

[confirm]

[OK]

Erase of nvram: complete

Switch#reload

2) Deleting the switch Vlans

The strange part is that after deleting the switch configuration you will notice that the Vlans are still there.

Switch#show vlan brief

2   VLAN0002                         active
3   VLAN0003                         active
4   VLAN0004                         active

By executing the command “show vlan brief” you can see that there are 3 vlans configured on the switch. These vlans are stored in a file in flash memory called “vlan.dat” as we mentioned at the beginning of this article. You can see this file if you read what is stored in the flash:

Switch#show flash:

Directory of flash:/

1  -rw-     4414921          <no date>  c2960-lanbase-mz.122-25.FX.bin

2  -rw-         616          <no date>  vlan.dat

64016384 bytes total (59600847 bytes free)

As you can see from output above, the file “vlan.dat” is stored in flash. You have to delete this file in order to completely erase all vlans on the switch.

Switch#delete vlan.dat

Delete filename [vlan.dat]?

Delete flash:/vlan.dat? [confirm]

Note:

Depending on the Switch version, you might need to use command “delete flash:vlan.dat” instead of the above.

Switch#sh flash

Directory of flash:/

1  -rw-     4414921          <no date>  c2960-lanbase-mz.122-25.FX.bin

64016384 bytes total (59601463 bytes free)

Switch#reload

After executing the command “delete vlan.dat” just hit enter twice and it will be gone. Then you have to reload the switch.

Cisco Nexus Switches (NX-OS)

For Cisco Nexus Switches (running NX-OS software) the situation is different. Normally the VLANs configured on the switch are stored inside the running-configuration of the device and there is no vlan.dat file in the flash.

So basically by erasing the startup-config and then rebooting, it will normally delete also the VLANs.

Use the command “write erase” and then reboot the device.