VLANs across a WAN link?

John Blakley · ‎10-06-2008

I've had another question asked that I don't know the answer for. I have two sites connected point-to-point. They are on separate subnets: 10.1.2.0 / 10.1.102.0. The 10.1.102.0 network gets dhcp addresses from the 10.1.2.0 side. I've been asked to flatten the network that would allow all addresses to be on the 10.1.2.0/24 subnet.

I think I need to create VLANs for both sides. I'm not sure where to start, but I think I need to rip the address off of the fa0/0 interface for the 10.1.2.0 network, and create subinterfaces on fa0/0 like fa0/0.3. I would then attach it to VLAN 3, and do the same for the other side. Now, what happens to VLAN 1 on the 10.1.2.0 side? I can't just keep the VLAN 1 without an address, can I? Will clients on the 10.1.2.0 side be able to connect to the router at all if there's not a VLAN 1? Can I just have the VLAN 3 listed in the router and be okay?

Maybe this falls under campus VLANs, but I've never done it before.

Thanks!

John

HTH, John *** Please rate all useful posts ***

satish_zanjurne · ‎10-06-2008

Hi ,

if you want to flatten the network to have only one big subnet

1.Your link between two sites no longer remain L3 link.

2.No need of router

3.You need to extend the vlan's to other site, just the way you configure trunk

4.Your link between 2 sites will terminate on L2 switch.

5.Ports on which L2 link will terminate will be trunk , if multiple vlan's are there.

6.As this will be flat network, DHCP will also function properly, without any additional configuration

7.If you want intervlan routing ,then you need to use either L3 switch or Router.

HTH..rate if helpful..

John Blakley · ‎10-06-2008

You said that I don't have a need for a router, but this is a point-to-point T1 link.

HTH, John *** Please rate all useful posts ***

Jon Marshall · ‎10-06-2008

John

As Satish has stated you could remove the routers and treat the P2P link as a L2 link to extend your vlan.

However it may not be as simple as this dependant upon the topology you have and the P2P setup with your provider. Another way of extending a vlan is to use L2TPv3 which allows you to extend a L2 vlan over a L3 routed network. You would need to check whether your routers supported this.

http://www.cisco.com/en/US/docs/ios/12_3t/12_3t2/feature/guide/gtl2tpv3.html

Jon

John Blakley · ‎10-06-2008

So the provider's routers would need to stay there, and they would bridge between the sites for me? I'm going to read the documentation that you sent me, but this is something that I think we're going to pursue in other areas of our network as well.

HTH, John *** Please rate all useful posts ***

Jon Marshall · ‎10-06-2008

John

Do the vlans have their L3 interface on routers managed by the provider. If so i don't know how happy your provider would be to configure this for you.

Usually your vlan L3 interfaces would terminate on your equipment and the L2TPv3 tunnel would be transparent to your service provider.

Note that there are alternative solutions ie. EoMPLS (Ethernet over MPLS), VPLS (Vitual Private Lan Services) but you need to be subscribed to MPLS for these services.

Jon

Jon Marshall · ‎10-06-2008

John

One other option that i should mention. Here in the UK we have what are called LES circuits (LES = Lan Emulation Services). You don't have to be suscribed to MPLS to get them, they are in effect just P2P links that you can treat as a L2 link. They do have a distance limitation.

I suspect this type of service is available in other countries as well.

Jon