Networking across campus with multiple ISPs

Question

I currently have a campus that gets service from two ISP's that are each connected to their own router. The ISP's ingress and their routers are in different buildings on the campus. The buildings are not networked currently.

I have a requirement to install cameras across campus and have those networked into a single NVR and accessed by a browser anywhere on campus. There is no other requirement for load balancing across ISP's or need for redundancy. The only requirement is to receive video feed from the cameras to the NVR and play/replay on a computer browser on either network.

From a physical wiring standpoint, I can easily connect the networks from a switch in one building to a switch in another. I cannot so easily connect the two routers together directly without going through a switch. Any ideas on a fairly simple solution to this problem would be appreciated.

Answer 1

The easiest method is to connect the two routers using a dedicated, routed port on a small transfer subnet (/30 or /31) and add a static route to the remote network on each side. If network addresses overlap you need to renumber one of the subnets (thx @Ron).

If each network connected to a local router is just a single subnet then that's all there is to it (otherwise add more static routes as required).

If you can't use additional, routed ports on the routers, you can add a router or L3 switch in between, connected to both networks, and add a static route to the remote network on each WAN router with the new router as gateway.