Opening a port for League of Legends is a relatively simple process, but there are many different things that you can do to open your router's ports.

How to See the Ports That Are Blocked on a Router. By default, Windows and the network router open some ports used for Internet and Web applications such as email, browsing, FTP file transfers and ...

Computers should not be connected to a router's WAN port, as this would prevent data from entering or exiting the network. Instead, a computer should be connected to a router's local area network ...

Cause from what I can see on that router it is a DSL router (DSL dedicated WAN port) with a 4 port switch and a wireless AP in it. It can't talk to a cable modem as a router.