Well they act as a phisic firewall, u have to open ports by entering in ur router homepage (ur ip in iexplorer) but u shall know the password, then when u acces the router homepage(it's bios) i gotta open ports in NAPT settings, the way of doing it depends on ur router (u can tell ur ISP to set ur router to monoport instead of multiport so it's just like a moded, but only if u have only 1pc connected to it)