Regarding bridge mode e.g. one has a router-modem(as in 'home router' so it does NAT too and also a modem inside), and a router(i.e. a 'home/NAT router' with no modem), and one wants to connect them.

If you've ever poked around your router settings, you might have come across something called "Bridge Mode." It sounds technical (and, well, it is), but the concept is actually pretty simple. Bridge ...