For fiber, your router needs the right WAN connection, speed support, and Wi-Fi capabilities. Routers designed for DSL (which uses phone line inputs) or cable (which uses coaxial inputs). Most fiber ISPs, including Mercury, provide an ONT that connects directly to your router via an Ethernet cable. This means you don't need a specialized modem-router device, but your router must support high-speed Ethernet input. While many users ask if fiber internet needs a modem, it actually. To connect your fiber optic cable to a router, ensure you have the following: Fiber optic modem (ONT): Most fiber connections require an Optical Network Terminal (ONT), provided by your ISP. You need a modem or ONT to do so.