Explainer · Networking
Router vs modem: what each one does, and whether you need both
The modem brings the internet into your home. The router shares it with your devices. Here is how to tell which boxes you have and what to buy.
If your internet comes through a cable in the wall, there are two jobs to be done: translating your provider's signal into a normal internet connection (the modem's job) and sharing that connection with every phone, laptop, TV, and smart plug in the house (the router's job). Sometimes those are two boxes. Often your provider gives you one box that does both.
Router vs modem at a glance
| Device | What it does | Has Wi-Fi? | Who usually supplies it |
|---|---|---|---|
| Modem | Connects to your provider over coax (cable) or phone line (DSL); outputs one internet connection | No | You or your provider |
| ONT | Fiber's version of a modem: converts the fiber signal to Ethernet | No | Your fiber provider |
| Router | Shares one connection with many devices, assigns local addresses, firewalls, creates Wi-Fi | Yes (wireless router) | You or your provider |
| Gateway / modem router combo | Modem and router in one box | Yes | Usually your provider; can be bought |
| Mesh system | A router plus satellite units that spread Wi-Fi through the home | Yes | You |
| Extender / access point | Adds Wi-Fi coverage from an existing router | Yes | You |
What a modem does
A modem speaks your provider's language. On cable internet that is DOCSIS over a coaxial cable; on DSL it is the phone line. It produces a single internet connection on an Ethernet port, which is meant for one device — the router. Modems have no Wi-Fi and do not protect your devices from the internet. Fiber homes do not have a modem; they have an ONT that does the same job.
What a router does
A router creates your home network. It hands out local IP addresses, uses NAT so all your devices can share one public address, blocks unsolicited traffic with a firewall, and (on a wireless router) broadcasts Wi-Fi. It is also where you set your Wi-Fi name and password, parental controls, guest network, and device priorities.
Do you need both?
- Cable or DSL: yes, either two boxes or one gateway that does both.
- Fiber: an ONT (from your provider) plus a router. Some fiber providers combine both in one unit.
- 5G home internet or Starlink: the provider's unit is already a modem and router; add your own router or mesh only if you need better Wi-Fi.
How to tell what you have
- Coax cable plugged in and no Wi-Fi name on the label: a modem.
- Coax cable plugged in and a Wi-Fi network name and password on the label: a gateway (modem router combo).
- A thin fiber cable or a box labeled ONT or ONU: a fiber terminal.
- Several antennas, several Ethernet ports, and a WAN or internet port, with no coax jack: a router.
Combo gateway vs separate modem and router
| Gateway (combo) | Separate modem + router | |
|---|---|---|
| Setup | One box, one app | Two boxes, one extra cable |
| Wi-Fi quality | Usually average | Pick any router or mesh system |
| Upgrading Wi-Fi | Replace the whole unit | Replace only the router |
| Cost | Rental fee or one purchase | Two purchases; no rental |
| Best for | Small homes, simplicity | Larger homes, mesh, enthusiasts |
How to connect a router to a modem
- Power off the modem or ONT.
- Connect an Ethernet cable from the modem's Ethernet port to the router's WAN or internet port.
- Power on the modem and wait until its online light is solid, usually one to five minutes.
- Power on the router and follow its app or web setup to name your Wi-Fi.
- If you replaced an older router, reuse the same Wi-Fi name and password so your devices reconnect on their own.
Which should you buy?
If you are on cable and want to stop paying an equipment fee, buy a DOCSIS 3.1 modem router combo from your provider's approved list (see our best modem router combos). If Wi-Fi coverage is the problem, keep or buy a modem and pair it with a good router or mesh system. On fiber, you only need the router.
Questions we get
What is the difference between a modem and a router?
A modem connects your home to your internet provider's network and gives you one internet connection. A router takes that one connection and shares it with all your devices, over Wi-Fi and Ethernet, while acting as a firewall. Many providers supply a gateway that combines both.
Do you need a modem to use a router?
You need something that connects to your provider. On cable internet that is a modem; on fiber it is an ONT; on 5G home internet or Starlink it is the provider's own unit. A router on its own cannot reach the internet, but it can still run a local network between your devices.
What does ONT mean?
ONT stands for optical network terminal. It is the box your fiber provider installs that converts the light signal on the fiber line into Ethernet. It does the modem's job on a fiber connection, and you plug your router into it.
Do you just plug in a new router?
Mostly. Turn off the modem or ONT, connect the new router's WAN or internet port to it with an Ethernet cable, power the modem back on and wait for it to come online, then power on the router and run its setup app. If your provider's box also has Wi-Fi, put it in bridge mode so you do not have two routers.
Where should you not put your router?
Avoid cabinets, the floor, behind a TV, next to a microwave or aquarium, inside a closet, and at the far end of the home. Put it central and high, in the open, near where you use the most devices.
How often should I replace my router?
Every four to six years for most people, or sooner if it stops receiving firmware updates or cannot keep up with your plan. Modems last longer; replace a cable modem when your provider stops supporting its DOCSIS version or you upgrade past its speed.