We don't know how your network is setup, so we can't really answer on that. Usually you should be able to connect to another computer on the same subnet. You can try to ping it but make sure the firewall is not blocking your requests. Usually no port forwarding is needed on the LAN, this is commonly used when someone from the internet needs to connect to a host on your LAN over a router.
If you don't use the master server and just want it to be within the local LAN, you must either: 1. Implement the detection yourself, thats normally done through UDP Broadcast into the same subnet 2. Invest into something like MuchDifferent Unity Suite and use uLink instead of Unity Networking which offers it out of the box
I am not quite sure why are you are trying to connect to your router? If you want to connect to another pc on the LAN you need the IP address of that pc...not the router.