Routing between two networks

Question

I had a question here.

Basically, we have two different networks. Each network has one Cisco 2960 layer 2 switch for each network in the same location. These are two individual networks. There is a link from each switch to a service provider router. The service provider has provided us two interfaces on their router, one for each network. The default gateway on each switch is the inside interface IP of the router. The service provider router does all the routing before sending it out WAN to our data center.

Attached is a quick drawing put together.

Now, we have a backup server connected to each switch for each network. In an attempt to reduce the number of backup servers, management has asked us to reduce to one backup server (for both networks) and use the other backup server as spare. My question is, how can we route between the two networks, for the sake of using single backup server. The users should still be on separate networks. Do we need to put a layer 3 device to perform the routing? Or can we add some kind of static routes on our layer 2 switch to the service provided router since it is doing all the routing? Can someone please comment?

Answer 1

Attached is a quick drawing put together.

I can't see a drawing. Did you forget to upload it or is my browser playing up?

Each network has one Cisco 2960 layer 2 switch for each network in the same location. These are two individual networks. There is a link from each switch to a service provider router. The service provider has provided us two interfaces on their router, one for each network. The default gateway on each switch is the inside interface IP of the router. The service provider router does all the routing before sending it out WAN to our data center.

As the ISPs router has a leg in both networks you should be able to route between them the networks using that router. You wouldn't need to purchase any additional equipment or use an additional network card.

A good way to test this theory is to ping from a PC in one network to the backup server in the other network. If this works then your backups will work too.

Answer 2

You cannot do this at layer-2. Layer-2 doesn't understand routers or IP. You must use a layer-3 device (router). You need to put a router between the networks. A layer-3 switch contains a router. You have to evaluate your needs, but it could be that either a stand-alone router or a layer-3 switch may work for your requirements. Routers route between networks.

Answer 3

Yes, just plug backup server into each switch. Obviously, backup server will need 2 NIC's, one for each connection. That takes care of layer 1 and layer 2 connectivity.

To get the backup server online you need to setup layer 3, or IP addressing and routing. DHCP will need to be disabled on the backup server. You will need to manually address each NIC and add some host routes on the server. A preferred default gateway and a less preferred default gateway, plus any other routes pointing to respective subnets.