What is the difference between a modem and a router?
They solve different problems and are often combined in one box, which is why the distinction gets lost. A modem connects your home to your internet provider, translating between the signalling used on their line and standard networking. A router creates and manages your local network, deciding where traffic goes and allowing many devices to share the single connection the modem provides.
Without a modem you have no path to the internet at all. Without a router you could connect exactly one device, and it would sit directly exposed to the internet with no local network behind it.
Most equipment supplied by providers combines both, plus a wireless access point and a small switch, into a single unit usually called a gateway. That is convenient but it is why people describe one box using either word and both are partly right.
The distinction becomes practical in a few situations.
- Replacing hardware. If your wireless coverage is poor but the connection is fine, you need a better router or access point, not a new modem.
- Adding your own router to provider equipment. Running two routers in series creates a double layer of address translation, which usually works for browsing but breaks incoming connections, some games and remote access. Putting the provider unit into a pass-through or bridge mode avoids it.
- Diagnosing faults. A modem problem affects everything and often shows on the device status lights. A router problem may affect only wireless devices, or only some traffic.
Knowing which function is failing narrows troubleshooting considerably, even when both live in the same plastic case.