Yes, you can often use your existing router with fiber optic internet, but there are crucial considerations. Understanding compatibility, potential limitations, and when an upgrade is necessary will ensure you get the most out of your high-speed connection. Routers designed for DSL (which uses phone line inputs) or cable (which uses coaxial inputs) won't work. This guide will break down everything you. Unlike cable internet, fiber connections do not require a cable modem. Many major ISPs, such as Verizon and Xfinity, offer fiber connections directly to your door, known as FttP or Fiber. The ONT is your modem equivalent in a fiber setup.