One network 2 buildings

Unanswered Question
Nov 3rd, 2009

I have a network that will be extended to another building. I have all the vlans defined in router Bldg1. The connection to Bldg2 is using a Layer2 switch with a routed link thru fiber. How I can transfer the vlan information from the other Bldg ?

Thanks!

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johgill Tue, 11/03/2009 - 16:12

Maria,

The answer will depend on the hardware you are using.

What is the router used in bldg 1, what is the switch in bldg 2?

Most likely you can use a trunk, but how you integrate that into the bldg 1 router depends on the hardware and the way you are currently switching and routing there.

maria.melendez Tue, 11/03/2009 - 16:17

Bldg 1: Cisco 3550 with routed link with fiber to another RouterA containing F/W

Bldg 2: Cisco 4506 that will have a routed link with fiber to RouterA.

At this point, all my vlans are in the Cisco 3550 with ip routing and ip route commands. Also VTP is configured as server.

pkurdziel Tue, 11/03/2009 - 16:16

VTP and set up trunk ports on each switch.

One switch should be the VTP server and the other should be a VTP client. Be aware that introducing a switch with a higher revision number can cause problems because the config from the switch with the higher revision number is applied.

You can configure the new switch as vtp transparent and manually configure the vlan information.

maria.melendez Tue, 11/03/2009 - 16:19

My problem is that both switches will be connected thru a routed link with fiber.

johgill Tue, 11/03/2009 - 18:28

Maria,

It sounds like you are required to have a routed link here, is that true?

If you have to stick with a routed link, you will not be able to use the same VLANs. You can re-use the VLAN numbers in the new building, but that will not give connectivity to the corresponding bldg 1 VLAN with that number.

Some other routers can use L2TPv3 in order to make an xconnect, which transports L2 over a routed hop. Unfortunately, your switches do not support this feature.

Now, if you have some leeway in your configuration, I would suggest trunking over to the new building, and the routed interface on the 3550 be converted to an "interface VLAN" which can still route when necessary.

The VTP discussion is an afterthought, you can use it or not, but it doesn't really matter unless you have L2 connectivity anyway. I prefer to keep VTP out of the equation unless you have LOTS of switches and LOTS of VLANs.

maria.melendez Thu, 11/05/2009 - 07:21

We are going to put a 3750 at the top of our network architecture and using trunk ports to connect Bldg1 and Bldg2. In that way, I 'll be able to use VTP for my vlans.

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