A modem and a router do different jobs, so using one as the other will not work

A modem connects you to your internet service provider. A router takes that connection and shares it among your devices. They are separate tools that do separate things. You cannot use a modem as a router, and you cannot use a router as a modem — each one lacks the hardware and software the other needs.

That said, some devices blur the line. A gateway or combo unit combines modem and router functions in one box. If your ISP gave you a single device, it is likely a gateway, not a modem alone. That device can do both jobs because it has both sets of components built in. But a standalone modem — the kind that plugs into a wall outlet and a coaxial cable — cannot replace a router on its own.

Key Takeaways

  • A modem connects to your ISP; a router shares that connection to your devices — they perform opposite functions and cannot substitute for each other.
  • A gateway or combo unit combines both modem and router in one device and can handle both jobs, but a standalone modem cannot.
  • If you rent your modem from your ISP, replacing it with a router will cut off your internet entirely because the router has no way to talk to the ISP's network.
  • Buying your own modem and router gives you more control and often costs less over time than renting from your ISP.

Why a modem cannot do what a router does

A modem has one job: translate the signal from your ISP's network into data your devices can use. It has one port for the ISP's cable (coaxial, fiber, or phone line, depending on your service type) and usually one or two ports for devices to plug in directly. That is it. It does not have the ability to create a wireless network, assign local addresses to multiple devices, or manage traffic between them.

A router, by contrast, takes the internet connection from the modem and broadcasts it wirelessly to all your devices at once. It assigns each device a local address on your home network, keeps track of which data goes where, and handles security by filtering unwanted traffic. A modem has none of this logic. Even if you could somehow plug multiple devices into a modem's ports, the modem would not know how to talk to more than one at a time.

What happens if you try to use only a modem

If you unplug your router and try to use only your modem, you will have internet on any device you plug directly into the modem's ethernet port — but only one device at a time, and only if the modem has more than one port (most do not). You will have no wireless network. Any device that relies on Wi-Fi will not connect.

More importantly, if your modem is rented from your ISP, the ISP has configured it to work only as a modem. It will not have router features turned on, and you cannot turn them on yourself. The device is locked to a single function. If you own your modem outright, you still cannot add router features — the hardware straightforward does not exist inside the box.

When you actually have a gateway, not a modem

Many ISPs ship a single device that looks like a modem but is actually a gateway. Common examples include the Comcast Xfinity Gateway, the Verizon Fios router, and the AT&T BGW210. These devices have a coaxial or fiber port on the back (to connect to the ISP) and Wi-Fi built in. They are doing both jobs at once.

If you have a gateway, you already have a router. You do not need a separate one unless you want to replace it with a better model or extend your Wi-Fi range. If you do want to replace it, you will need to keep the gateway connected to the ISP's line — you cannot remove it. Instead, you would connect your new router to one of the gateway's ethernet ports and put the gateway in bridge mode (a setting that turns off its router features and lets your new router take over). Check your ISP's documentation or call their support line to learn how to enable bridge mode on your specific gateway.

Renting versus buying your own modem and router

Most ISPs charge a monthly rental fee for the modem or gateway they provide — typically between $10 and $15 per month. Over three years, that adds up to $360 to $540 for a device you do not own. Buying your own modem and router costs more upfront but pays for itself within two to three years, and you keep the devices when you switch ISPs.

If you buy your own equipment, you need to choose a modem that works with your ISP's network type. Comcast uses DOCSIS 3.1 modems. Verizon Fios requires a specific router model. AT&T fiber has its own requirements. Check your ISP's approved equipment list before you buy. Once you have a modem, you can buy any router you want — they are not locked to a specific ISP.

Buying your own also means you control when you upgrade. ISP-provided equipment is often older and slower than what you can buy separately. If your Wi-Fi is slow or your connection drops often, a newer modem and router will usually fix it faster than calling your ISP's support line.

How to set up a modem and router together

If you buy your own modem, the setup is straightforward. Plug the modem into power and connect the ISP's cable (coaxial, fiber, or phone line) to the port labeled "In" or "ISP." Wait two to five minutes for the modem to boot and connect to the ISP's network — you will see lights on the front change from red to green. Then plug an ethernet cable from one of the modem's ethernet ports into the "WAN" or "Internet" port on your router.

Power on the router and wait another two to five minutes. Once the router's lights stabilize, open your phone or laptop and look for the router's Wi-Fi network name in your available networks list. It is usually printed on a sticker on the router's back. Connect to it, enter the password (also on the sticker), and you are online. You can change the network name and password later by logging into the router's settings page — the address is usually printed on the sticker as well, something like 192.168.1.1 or 192.168.0.1.

Frequently Asked Questions

Can I use a modem without a router?

Yes, if you only need to connect one device via ethernet cable. Plug the device directly into the modem's ethernet port and it will have internet. You will not have Wi-Fi, and you cannot connect multiple devices wirelessly. For any household with more than one device, you need a router.

What if my ISP will not let me use my own modem?

Some ISPs, particularly smaller regional providers, do not allow customer-owned modems. Call your ISP's support line and ask which modems are approved for your account. If they do not approve any, you will have to rent. Some ISPs also charge a higher monthly fee if you use your own modem, so ask about that too before you buy.

Can I use two routers instead of a modem and router?

No. A router cannot connect directly to your ISP's network — it has no way to understand the ISP's signal. You always need a modem between the ISP's line and your router. You can use two routers together if you want to extend your Wi-Fi range, but the first router must still be connected to a modem.

Is a gateway better than a separate modem and router?

A gateway is simpler to set up and takes up less space. A separate modem and router gives you more control, lets you upgrade each piece independently, and often performs better because each device is optimized for one job. If your ISP's gateway works well for you, there is no need to change. If you want faster speeds or better Wi-Fi coverage, buying your own usually helps.

What should I do with my old modem if I buy a new one?

If it is rented from your ISP, pack it up and return it to avoid a non-return fee. If you own it, you can sell it online, donate it, or recycle it through an electronics recycling program. Check your city or county's website for local e-waste drop-off locations.