How to configure multihomed computer to force internet requests over one of the adapters?

Question

Here is the setup.

Laptop is connected via ethernet adapter to a consumer grade wireless router. This router does not have a connection to the internet. It is local only and should stay that way for other connected clients.

Laptop connects via wireless adapter to a mobile hotspot.

The laptop needs to be on the local network, while also being able to access the internet over the mobile hotspot. Other clients connected to the wireless router would not get internet.

Perhaps a different way to put it is how to configure the computer direct any request over the mobile hotspot that is not a request to the local networks subnet?

Answer 1

Best answer: See this post on subnetting on our sister site serverfault.

The short answer:

• Set your default route to the mobile hotspot. Any access to a computer or network not in the routing table will go that way.
• Add explicit routes for your local network.
• Done!

Now when your computer tries to access another computer it will look if it has a way to reach it. If it is a local computer then it will find the route you added in step #2 and use that. If it does not find it (e.g. for the millions of computers on the Internet) it will fall back to the default gateway, which you pointed via to the hotspot.