Catalyst switch upgrade question

Answered Question
Mar 10th, 2009

I currently have 5 Catalyst 3548XL switches connected through Gigastack modules that are the backbone of my LAN. They are setup in a VTP domain but changes are rarely, if ever, made.

I need to replace one of them with a new 3560 but the one I need to replace is the VTP server. What should I do?

Should I copy the config from the 3548 (can I even do that) and have this new 3560 set as a server when I connect it?

Should I set all the switches to VTP transparent mode? Will this cause an issue or wipe all the current config information on switches that are currently in VTP Client mode?

I have this problem too.
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Correct Answer by Jon Marshall about 7 years 9 months ago

The horror story is if you introduce a new switch with a higher configuration revision number and it then overwrites the existing vlan database on all your live switches with it's own which is usually just vlan 1. The switch you introduce doesn't even have to be a VTP server, it can be a VTP client.

So the key thing is the configuration number. So i would do this

1) Your existing VTP server should have the correct vlan database.

2) Choose one of your other switches in the stack and change it from VTP client to VTP server. Before you do this check it has the same revision number as your existing VTP server but it should do as it is a live switch.

3) There is no need to demote your existing VTP server. You can have 2 VTP servers or more if you wish and most networks do have at least 2 VTP servers.

The new 3560. Before connecting it to the other switches log in and change it to VTP transparent then back to VTP client. This will set it's configuration revision number to 0 which is what you want.

Connect it to the other switches and let it get the VTP updates. Then it's up to you whether you leave it as a VTP client or promote it to a VTP server.

As i said before the key to all this is the revision number.

For reference if you have 2 VTP servers with the same revision number and you add another vlan for example on switch1 then switch1 will have the higher revision number and all the other switches, the VTP clients AND the other VTP server will update their databases with the new vlan as they will all have a lower configuration number.

Jon

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Jon Marshall Tue, 03/10/2009 - 07:42

You can simply make another one of your existing 3548XL switches a VTP server and then introduce the 3560 as a client and let it pick up the vlan database from the VTP server.

There is nothing wrong with having multiple VTP servers, they won't conflict. You just update one of them and the changes are pushed out to both VTP clients and other VTP servers.

Jon

qbakies11 Tue, 03/10/2009 - 10:56

That sounds like the opposite of everything I have heard in the past. I've heard all these horror stories of how a new switch was added to a network and was accidentally in Server mode and it wiped all the other switches. Is that not true anymore?

If I were to make another switch the VTP server (a good idea) then would I make the current server a Client first and then 'promote' the chosen switch to Server mode?

Correct Answer
Jon Marshall Tue, 03/10/2009 - 11:04

The horror story is if you introduce a new switch with a higher configuration revision number and it then overwrites the existing vlan database on all your live switches with it's own which is usually just vlan 1. The switch you introduce doesn't even have to be a VTP server, it can be a VTP client.

So the key thing is the configuration number. So i would do this

1) Your existing VTP server should have the correct vlan database.

2) Choose one of your other switches in the stack and change it from VTP client to VTP server. Before you do this check it has the same revision number as your existing VTP server but it should do as it is a live switch.

3) There is no need to demote your existing VTP server. You can have 2 VTP servers or more if you wish and most networks do have at least 2 VTP servers.

The new 3560. Before connecting it to the other switches log in and change it to VTP transparent then back to VTP client. This will set it's configuration revision number to 0 which is what you want.

Connect it to the other switches and let it get the VTP updates. Then it's up to you whether you leave it as a VTP client or promote it to a VTP server.

As i said before the key to all this is the revision number.

For reference if you have 2 VTP servers with the same revision number and you add another vlan for example on switch1 then switch1 will have the higher revision number and all the other switches, the VTP clients AND the other VTP server will update their databases with the new vlan as they will all have a lower configuration number.

Jon

adamclarkuk_2 Tue, 03/10/2009 - 11:07

Those horror stories are very true but

it sounds like you have misunderstood, both Jon and myself are NOT saying add the new switch in as a VTP Server straight away, if you did do this and put it into your domain, then you would be living on of the nightmares you are talking about. By putting the new switch into client first, it will learn all the VLANS from ther server, therefore having the same config as the serve, then upgrading the switch to server. Even if you promoted one of your current switches to Server, he also will have all the up to date VLAN info so all is good.

adamclarkuk_2 Tue, 03/10/2009 - 07:43

Hi

You can have multiple VTP Servers in a switched network.

To be on the safe side, add your new 3560 as a client so that he gets all the VLAN information from the server, then once your happy all the VLAN config is there, upgrade him to a VTP server.

Setting the other switches to VTP transparent will not wipe out the current config, it will just stop them from acting on VTP updates they receive, although they will still pass the VTP advertisements on.

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