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New Member

Trunk VLANs across wide campus without down time

I have 4503 switches that have numerous 3com switches uplinked. There are several subnets being uplinked, all in vlan 1 (flat network).

I am in the process of seperating these in to vlans per each subnet.

My problem is this:

Some of the switches are spread out across a large campus and connected thru fiber.

Is there a way for me to set up the trunk ports and seperate everything into the vlans without taking things down?

My concern is, once I create the vlans for the different subnets on the 4503's, all other remote sites will loose connectivity (because they are uplinked with access ports at the moment, uplinking the different subnets)unitl I can set up the trunk ports on the remote end switch also, and it is going to take a while to get to everything (days).

Is there a way to do this a little at a time?

5 REPLIES
New Member

Re: Trunk VLANs across wide campus without down time

Rich,

This is kinda hard to answer without a lot more detail on your current setup, but I can certainly give you some ideas on how to start. A lot depends on how your current routing is setup and how each client has the existing subnet mask and gateway set up.

I'll assume you are working with 3com SS3300's or something similar, and that you will want to continue to remotely manage them. They have one major issue which I fought for a long time, until they were all replaced.:) They can only be managed via an address on Vlan 1. Therefore, as long as they are still in your network, you'll need to reserve vlan 1 as your management network. Not all that bad, just something to remember.

That said, the first thing I would do is take each link in turn, and convert it to trunking, creating and enabling all the new vlans on the trunk. If you can coordinate the changes on the uplink 4503 to being at the remote site to make the changes there, downtime should be minimal. For the moment, you can leave all clients on vlan 1.

Once that is done everywhere, you should be able to make changes only from your core location. How you proceed will depend on clients config and your routing config. You can create a new SVI interface at the core that match the clients expected gateway and then move them all to the new vlan on the remote switches. If you have clients at multiple remote locations that need to move to match the new routing, there could be some outages, but you should be able to keep it manageable.

No matter what, it will probably be painful. But when you get done, you will end up with a more manageable and extensible network.

Good luck. Hope this helps.

Roger

Re: Trunk VLANs across wide campus without down time

I agree with Roger on this. You should first start with trunking the each link connected to the 4503 ie. core switch.Another thing to take into consideration is the "NATIVE" vlan on Cisco 4503.On 3COM switches you have to TAG all the vlan except the one which is a native vlan on 4503 switch. By default Vlan1 is untagged on Cisco4503 so you have to untag vlan1 on 3COM switches.

Once that is done,start configuring layer2 vlan on 4503 switches and all the 3Com switches.Once that is done make the Layer3 SVI's on the 4503 for the respective vlans.

After that start moving the hosts to their respective vlans with Gateway configured as the L3SVI on 4503.Make sure that you set the correct gateway on all the hosts with their respective vlan interfaces.

You should be all good to go after that.Let us know if you have any problems in that.

HTH,please rate if it does.

-amit singh

New Member

Re: Trunk VLANs across wide campus without down time

Thanks for the great replys, they have been very helpful.

Once I create the trunking and leave all subnets in vlan1, I think everything will be ok up to that point. I can also creat the differnet vlans on each remote switch, just not add any ports just yet.

I think the problem will be when I create the differnet Vlans for each subnet on the 4503's.

I was aware of the 3com management being in Vlan1 only and I am going to move everything out of that vlan.

Right now all servers (10.10.150.0), clients (10.10.151.0) and printers (10.10.153.0) are all in vlan 1.

Once I do that, all remote clients, servers and printers will not communicate until I have those ports added to the respective vlan to be trunked up to the 4503.

And as you said, I can do this over a weekend maybe.

Does all the above look correct to you guys?

New Member

Re: Trunk VLANs across wide campus without down time

Thanks for the great replys, they have been very helpful.

Once I create the trunking and leave all subnets in vlan1, I think everything will be ok up to that point. I can also creat the differnet vlans on each remote switch, just not add any ports just yet.

I think the problem will be when I create the differnet Vlans for each subnet on the 4503's.

I was aware of the 3com management being in Vlan1 only and I am going to move everything out of that vlan.

Right now all servers (10.10.150.0), clients (10.10.151.0) and printers (10.10.153.0) are all in vlan 1.

Once I do that, all remote clients, servers and printers will not communicate until I have those ports added to the respective vlan to be trunked up to the 4503.

And as you said, I can do this over a weekend maybe.

Does all the above look correct to you guys?

New Member

Re: Trunk VLANs across wide campus without down time

Rich,

In exporing the possibility of not having to kill a weekend, have you considered doing the work in phases from least critical to most? If you have your vlan trunk port configurations pre-done as far as possible, and a good back-out strategy in case it doesn't go the way you expect, you might consider doing doing a least-critical change-over during lunch or in the late afternoon. If this goes well you could build on this positive experience in planning the more critical changes.

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