Note - You should read this article in its entirety before drawing any conclusions about the path(s) you want/need to take to overcome any problems that you may have.
Please take a moment to look at the following diagram:
|No, I do not claim to be an artist|
Do you see that vertical red bar that is going through the center of the router? I'm trying to show that the LAN and WAN sides of the router are blocked off from each other. This is actually not entirely true because the router does allow computers from the LAN to access the Internet (WAN), but devices and computers from the Internet (WAN) cannot access the devices and computers inside the LAN. This is by design.