Computer Certification

Passing the BCMSN exam and getting one step closer to the CCNP certification means learning and noticing details that you were not presented with in your CCNA studies. (Yes
I know – you had more than enough details then
right?) One protocol you’ve got to learn more details about is VTP
which seemed simple enough in your CCNA studies! Part of learning the details is mastering the fundamentals
so in this tutorial we’ll review the basics of VTP.


In show vtp status readouts
the "VTP Operating Mode" is set to "Server" by default. The more familiar term for VTP Operating Mode is simply VTP Mode
and Server is the default. It's through the usage of VTP modes that we can place limits on which switches can delete and create VLANs.

In Server mode
a VTP switch can be used to create
modify
and delete VLANs. This means that a VTP deployment has to have at least one switch in Server mode
or VLAN creation will not be possible. Again
this is the default setting for Cisco switches.

Switches running in Client mode cannot be used to create
modify
or delete VLANs. Clients do listen for VTP advertisements and act accordingly when VTP advertisements notify the Client of VLAN changes.

VTP Transparent mode actually means that the switch isn't participating in the VTP domain as Servers and Clients do. (Bear with me here.) Transparent VTP switches don't synchronize their VTP databases with other VTP speakers. They don't even advertise their own VLAN information! Therefore
any VLANs created on a Transparent VTP switch will not be advertised to other VTP speakers in the domain
making them locally significant only. (I know you remember that phrase from your CCNA studies!)

Devices running VTP Transparent mode do have a little something to do with the other switches in the VTP domain
though. When a switch running in Transparent mode receives a VTP advertisement
that switch will forward that advertisement to other switches in that VTP domain.

Configuring switches as VTP Clients is a great way to “tie down” VLAN creation capabilities to switches that are under your physical control. However
this occasionally leads to a situation where only the VTP clients will have ports that belong to a given VLAN
but the VLAN still has to be created on the VTP server. (VLANs can be created and deleted in transparent mode
but those changes aren't advertised to other switches in the VTP domain.)


In the next BCMSN tutorial
we’ll take a look at the details of VTP.

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.