Is it my router or my modem?

Acutis · plain-English network help · updated June 2026

When the internet goes down, people poke at "the box" without knowing which box does what. The two devices have very different jobs, and telling them apart is the key to fixing the right one. Here is how to know which is which, read their lights, restart them properly, and decide which one to replace.

Is it my router or modem? What each one does

The modem is your bridge to the outside world. It connects to your internet provider's line (cable coax, fibre, or phone) and turns that signal into something your home network can use. One job: get you onto the internet.

The router sits behind the modem and shares that one connection with all your devices. It hands out local addresses, runs your Wi-Fi, and keeps devices talking to each other. So when you ask "is it my router or modem," you are really asking: is the problem getting onto the internet (modem) or sharing it around the house (router)?

Many providers give you a single combo unit (a "gateway") that does both jobs in one box. If you have only one device with a coax or fibre cable going into it and Wi-Fi coming out, you have a combo unit, and the troubleshooting below applies to the one box.

Reading the blinking lights

The lights tell you almost everything. Labels vary by brand, but the meaning is consistent.

On the modem

• Power: solid means it has power.
• Downstream / Upstream (or DS/US): solid means it has locked onto your provider's signal. Blinking for a long time means it is failing to connect to the provider, an outside-the-home problem.
• Online / Internet: solid means the modem has a working internet connection. If this light is off or blinking, the internet is not reaching your home, so the router is not the issue.

On the router

• Power and Wi-Fi: solid means it is running and broadcasting.
• Internet / WAN: this shows whether the router is receiving a connection from the modem. If it is off but the modem's Online light is solid, the link between the two is the problem.

The quick read: if the modem's Online light is off, the fault is the modem or your provider. If the modem is online but the router's internet light is off or you have no Wi-Fi, the fault is the router.

The right restart order

Restarting fixes a surprising share of outages, but only if you do it in the right order so each device gets a fresh connection from the one before it.

1. Unplug both the modem and the router from power.
2. Wait a full 60 seconds. This lets the modem fully drop its old session with the provider.
3. Plug in the modem first. Wait until its Online light is solid (one to two minutes).
4. Then plug in the router. Give it another minute or two to boot and pick up the connection.

If you have a single combo unit, just unplug it, wait 60 seconds, and plug it back in.

A simple test to isolate the culprit

If you have a separate modem and router, you can pinpoint the fault in two minutes:

1. Unplug the Ethernet cable from the router and plug it straight from the modem into a laptop.
2. Restart the laptop or release and renew its address.
3. If the laptop gets internet directly from the modem, the modem and your provider are fine, so the router is the problem.
4. If the laptop still has no internet straight off the modem, the modem or the provider is the problem.

Which one to replace

• Replace the modem if it repeatedly loses its Online light, drops the connection during the day, or is too old to support your current plan's speed. If you rent it from your provider, ask them to swap it first.
• Replace the router if the modem stays online but Wi-Fi is weak, devices keep disconnecting, or it cannot keep up with many devices. A router is also the part most worth upgrading for better Wi-Fi coverage.

Before buying anything, call your provider if the modem light points to an outside problem. Outages and line faults are theirs to fix, and replacing your own gear will not help.