Computer Certification

CCNA and CCNP candidates who have their own Cisco home labs often email me about an odd situation that occurs when they erase a switch's configuration. Their startup configuration is gone
as they expect
but the VLAN and VTP information is still there!

Sounds strange
doesn't it? Let's look at an example. On SW1
we run show vlan brief and see in this abbreviated output that there are three additional vlans in use:

SW1#show vlan br


10 VLAN0010 active

20 VLAN0020 active

30 VLAN0030 active

We want to totally erase the router's startup configuration
so we use the write erase command
confirm it
and reload without saving the running config:

SW1#write erase

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

[confirm]

[OK]

Erase of nvram: complete


00:06:00: %SYS-7-NV_BLOCK_INIT: Initalized the geometry of nvram

SW1#reload

System configuration has been modified. Save? [yes/no]: n

Proceed with reload? [confirm]

The router reloads
and after exiting setup mode
we run show vlan brief again. And even though the startup configuration was erased
the vlans are still there!

Switch#show vlan br


10 VLAN0010 active

20 VLAN0020 active

30 VLAN0030 active

The reason is that this vlan and VTP information is actually kept in the VLAN.DAT file in Flash memory
and the contents of Flash are kept on a reload. The file has to be deleted manually.

There's a little trick to deleting this file. The switch will prompt you twice to ask if you really want to get rid of this file. Don't type "y" or "yes"; just accept the defaults by hitting the return key. If you type "y"
the router attempts to delete a file named "y"
as shown here:

Switch#delete vlan.dat

Delete filename [vlan.dat]? y

Delete flash:y? [confirm]

%Error deleting flash:y (No such file or directory)



Switch#delete vlan.dat

Delete filename [vlan.dat]?

Delete flash:vlan.dat? [confirm]


Switch#

The best way to prepare for CCNA and CCNP exam success is by working on real Cisco equipment
and by performing lab tasks over and over. Repetition is the mother of skill
and by truly erasing your VLAN and VTP information by deleting the vlan.dat file from Flash
you'll be building your Cisco skills to the point where your CCNA and CCNP exam success is a certainty.