VTP server

This question is forked from the "Question about interVLAN routing" thread.

Webmaster wrote:

carveone wrote:

PS: While on the topic of vlans, is there any way of finding out who the vtp server is in a pile of switches? show vtp isn't telling me. Guess I have to telnet to each one and do a "show vtp" on each...

By default they are all servers. A proper way is to configure a vtp domain and explicitely configure two switches as VTP servers and the rest as clients. If you run 'sh vtp status' it will show whether it's a client or server (or transparent), hence Server by default. vtp domain name is NULL (not shown).

Two switches? Interesting. I was wondering if they'd fight given the revision numbering.

I understand they are servers by default. But say you had a ring of switches, one server and 3 clients and a console on one of the clients, where is the server? I don't believe there's any way to find out other than telneting to each one...

This is unlike spanning-tree - you can find out who the root bridge is by interpreting the cost outputs and designated bridge information from "show spanning-tree".

I'm asking leading questions here - you may have to find out all this information in the ccna exam

Conor.

PS: Would it be presumptious of me to want to write a technote for this for your site?!

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Comments

carveone

I may have answered my own question

Console> show vtp domain

Domain Name     Domain Index VTP Version Local Mode  Password
--------------- ------------ ----------- ----------- ----------
                1            2           server      -
 
Vlan-count Max-vlan-storage Config Revision Notifications
---------- ---------------- --------------- -------------
15         1023             5               disabled
 
Last Updater    V2 Mode Pruning  PruneEligible on Vlans
--------------- ------- -------- -------------------------
172.20.44.30    enabled disabled 2-1000
Console>

The "last updater field" is the "IP address through which VTP was last updated" according to the cisco docs (can you tell I don't have actual hardware!). Presumably this is the next hop up and would help rather a lot

This isn't in my CCNA book!

Of course neither is this:

                   [router]
  192.168.1.1/24    |    |   192.168.2.1/24
                    |    |
              [switch]  [switch]
                   \      /
                   [switch]

Any guesses to what happens here

I'm not just throwing silly nonsense out here I hope.

Conor.

mikej412

carveone wrote:
Console> show vtp domain

Are you on a CatOS switch? I'd ask one of my cats, but they are all catnapping.

S3750-1#show vtp ?
  counters  VTP statistics
  password  VTP password
  status    VTP domain status

S3750-1#show vtp status
VTP Version                     : 2
Configuration Revision          : 3
Maximum VLANs supported locally : 1005
Number of existing VLANs        : 8
VTP Operating Mode              : Server
VTP Domain Name                 : yourdomainhere.com
VTP Pruning Mode                : Disabled
VTP V2 Mode                     : Disabled
VTP Traps Generation            : Disabled
MD5 digest                      : 0x4B 0x00 0x05 0xF7 0xAC 0xB5 0xD3 0x2F 
Configuration last modified by 192.168.111.1 at 3-1-93 10:06:53
Local updater ID is 192.168.111.208 on interface Vl1 (lowest numbered VLAN interface found)
S3750-1#

carveone

mikej412 wrote:
carveone wrote:
Console> show vtp domain
Are you on a CatOS switch? I'd ask one of my cats, but they are all catnapping.

I'm afraid not. I took that output from the documentation from the Cat 5000 switches. Now that you mention it however, the options you show:

S3750-1#show vtp ?
  counters  VTP statistics
  password  VTP password
  status    VTP domain status

would be the only ones available normally. Certainly the only ones available in a sim. But the output of "show vtp status" you show also has a "local updater ID" part...

S3750-1#show vtp status
....
Local updater ID is 192.168.111.208 on interface Vl1 (lowest numbered VLAN interface found)
S3750-1#

Thanks,

Conor.

Webmaster

But say you had a ring of switches, one server and 3 clients and a console on one of the clients, where is the server? I don't believe there's any way to find out other than telneting to each one...

In that situation you configured 3 switches explicitly to be client, so you'll know which one is the server

It's not something automatically determined based on macs or priorities. The VTP mode has only local significance and dictates whether vlans can be created on the switches, and whether and how it will originate and/or forward updates. As for you picture, clients and servers forward VTP messages if the VTP domain name matches. And then I haven't even mentioned Transparent switches yet.

I think you are comparing VTP too much to STP. The VTP mode setting server is not 'the root' or something comparable. It's the switch on which you create VLANs, so you usually know which one it is. (You cannot create VLANs on a VTP client switch).

Two switches? Interesting. I was wondering if they'd fight given the revision numbering.

No they won't. Besides assuming you configure and apply vlan changes only on one server at a given time, the different VTP message types will prevent any confusion. If one server receive updates with a higher revision from another server it will accept them just as a client would. That said, if you only have two switches... well, with only two switches VTP doesn't really apply..., then you might as well leave them both as Server.

If you only have a single VTP server, and it goes down, the clients may lose there vlan config (they only store the VLANs in RAM). That's why it is important to have two VTP servers in a VTP domain. So, consider the VTP server as the switch on which you administer the domain.

This isn't in my CCNA book!

That's because VTP really is a CCNP - BSMSN topic. You'll need to know what it is for the CCNA, what it does, and how to setup a basic config, but in the BSMSN exam it is covered in much more detail.

The following two should give you a more complete picture (first one is good for all CCNA students:)

www.cisco.com/warp/public/473/vtp_flash/

Configuring VTP

carveone

Webmaster wrote:

But say you had a ring of switches, one server and 3 clients and a console on one of the clients, where is the server? I don't believe there's any way to find out other than telneting to each one...

In that situation you configured 3 switches explicitly to be client, so you'll know which one is the server It's not something automatically determined based on macs or priorities. The VTP

Oh yes, I understand VTP well. At least as well as my examprep book told me. The problem is if you didn't know which was the server. Say, in a CCNA simlet

In other words I got that question wrong and was trying to find out what I should have done! Still passed though!

I think you are comparing VTP too much to STP. The VTP mode setting server is
...
The following two should give you a more complete picture (first one is good for all CCNA students:)
www.cisco.com/warp/public/473/vtp_flash/

That's brilliant! Thanks for that link. It's always the edge conditions that catch you - the books describe how to set things up and what everything means, but the exams can ask questions on what happens when, say, a switch with a higher vtp revision is introduced. My book doesn't tell me...

Thanks,

Conor.