VTP Client/Server

[bdyzel]

I have a question that I'm just not sure about, and would dearly like some clarification on.

In the new 640-802 Sybex Manual, Chapter 9, page 565.
When you talk about "When to use VTP", you say at one stage that if I add a new switch to a existing switched network, that I have to make sure to configure it as a VTP client.
Because if I don't then it will be highly probable that the switch will send out a new VTP database to all other switches.

That makes sense, but I also went and had a look at the Cisco site here http://www.cisco.com/warp/public/463/vtp-flash/ (http://www.cisco.com/warp/public/473/vtp_flash/) (I hope I'm allowed to put this website in here), and when they talk about Common VTP Issues, they say that when adding a switch to an existing switched network, then it wouldn't matter whether the switch is in server or client mode, and that both modes would send out the updates to the other switches, overwriting the other switches configurations.

I think maybe it's switch dependent, maybe this will only happen on certain series of switches?

Does anyone know?

[aguilera]

You are absolutely right. Changing the VTP mode to Client alone will not prevent damage from being done!

Here are the steps you should take before adding a switch with a higher VTP revision that the VTP revision in the production environment.

1. Change mode of switch from either Server or Client to Transparent. (This sets the VTP revision to 0). Once you verify VTP revision is set to 0 [Show vtp status] you can set the VTP mode to Client mode.

or

Change the VTP Domain name, then change it back... this too sets the VTP revision back to 0. Once you verify VTP revision is set to 0 [Show vtp status] you can change the VTP mode to Client.

2. Bring up your trunks!


Give me a few minutes and I will draw up a couple of ppt slides and add them to this post. A quick down and dirty of VTP, VTP modes, and how both Servers and Clients send VTP updates.

aguilera

[aguilera]

Here is our switch topology.

[Client1]-----[Client2]-----[Client3]


Client1, Client2 and Client3 belong to VTP Domain AGUILERA.

Client1 and Client2 have default VLANs along with Production VLANs 10, 20, 30 and 40.
http://www.fidelisnetworks.com/client1vlan.jpg


Client3 has default VLANs and several other Non-Production VLANs
http://www.fidelisnetworks.com/Client3vlan.jpg

I issued the 'show vtp status' command on Client 3 and saw that the VTP mode was Client and revision was at a non zero number.
http://www.fidelisnetworks.com/c3vtptr.jpg

I verify vtp modes on Client1, Client2 and Client3 before I bring the trunk links up. "show interface trunk"

When I bring the trunk links up between Client1 and Client2 there are no changes because both switches have a VTP revision number of 0. Once I bring the trunk links up between Client2 and Client3... thats when the fireworks start. I go to Client1 and Client2... sure enough Client3 shared its VTP update with Client1 and Client2.

Here is some output from Client2.

1st you see vtp status rev 0, once I brought up the trunk links between Client2 and Client3, I issued sh vtp status and saw that the rev changed, I issued a show vlan and all production vlans were removed and replaced with no production vlans.
http://www.fidelisnetworks.com/tgtnhbd.jpg

All Production VLANs have been replaced by Non-Production VLANs because Client 3, operating in Client mode had a non-zero revison and sent out a VTP update.


*Things to keep in mind;

Changing the VTP mode from Server to Client does not change the VTP revision.

Changing the VTP mode from Server to Transparent does change VTP revision, but does not allow the Transparent switch to apply VTP updates to it's VLAN database.

I took several snapshots of changing VTP modes. I will post them under the Resetting VTP Revision number.

D. Aguilera

[bdyzel]

Thank you. :smile::smile:

[Brandon]

Keep in mind, it doesn’t matter if two switches are both servers, both clients, or one of each. Yes, you can have more than one VTP server.

In any combination of VTP servers and clients what happens is two switches talk back and forth, and then to replicate the database the switch with the latest VTP configuration revision number sends out the database they have. A higher number is the latest and greatest when it comes to VTP configuration revision numbers.

The receiving switch (remember, this could even be a client telling a server what to do here; not intuitive whatsoever!) will gladly accept the new database, wipe out what it shows for VLANs in its database, and overwrite with the list of VLANs from the other switch. This is a replace. NOT a merge.

Also, you should be aware that a few things need to be in place before two switches will replicate:

-They must have a trunk set up between them.
-They must have the same VTP domain name. (Case-sensitive)
-They must have the same VTP password. (Case-sensitive)



Best regards,

Brandon

[lammle]

Brandon, thank you for clarifying the three most iVTP mportant bullet points you must know when studying the CCNA objectives! :p
Cheers!
Todd Lammle

[siyadheen]

So... can I make a conclusion that "it dosent matter whether a switch is a VTP server or client when joining it to an existing VTP domain, all you have to bother about the revision number" right?