The technician calls it a modem, the box says router, and the settings panel mentions an ONT. All three refer to the same box in the corner of the room.
While everything works, the distinction doesn't matter. It only becomes relevant when you want to replace one of them, or when a technician asks you something you don't understand.
Three different jobs
| Device | Its job | Analogy |
|---|---|---|
| Modem / ONT | Translates the signal from the provider | A translator |
| Router | Shares the connection among many devices | A traffic controller |
| Access point | Broadcasts the Wi-Fi | A loudspeaker |
The signal arriving from the provider, whether as light in optical fibre, electricity in copper, or radio waves, cannot be understood directly by your laptop. The modem or ONT translates it.
Once translated, there's only one connection. The router shares it among all your devices, gives each a local address, and manages the traffic. How that address allocation works is covered in the guide to local IPs and DHCP.
The access point turns that connection into radio waves. In home equipment, all three functions sit inside one box.
Why fibre uses the term ONT
ONT stands for Optical Network Terminal. It's a modem, but specifically for fibre networks.
One thing sets it apart from an ordinary modem, and it matters: the ONT is registered on the provider's network. Each unit has a serial number their system recognises. You can't replace it by buying your own, because a new unit won't be recognised until the provider registers it.
This explains why providers let you replace the router but not the ONT, and why the PON and LOS lights live on this device, both report the state of the fibre line. Their meanings are explained in the guide to router indicator lights.
When the supplied router isn't enough
Provider-supplied equipment is generally adequate for a small home, but starts to struggle in a multi-storey house or as device numbers grow.
You don't need permission to add your own router. There are two ways:
Bridge mode, the tidier option
The supplied device is set to stop being a router and simply pass the connection through. Your router takes over all management duties. The result is clean: one layer of NAT, one place to configure.
The drawback is that not every provider allows it, and some lock this menu. You may need to ask customer service.
As an extra access point, the easier option
The supplied device remains the router, and your second router acts as an additional transmitter with DHCP turned off. No permission needed from anyone, and the full steps are in the guide to setting up two routers on one network.
Avoid stacked NAT. Connecting a second router via its WAN port without configuring anything creates two layers of address sharing. Devices on either side then can't see each other, and some applications break. This is the most common mistake when adding a router.
Working out which one to replace
| Complaint | What to address |
|---|---|
| Signal doesn't reach the back bedroom | Access point, add one, don't replace |
| Many devices, everything slows | A more capable router |
| LOS light is red | The fibre line, contact the provider |
| Internet completely down, lights normal | Authentication, contact the provider |
| Speed doesn't match the plan | Test over cable before concluding anything |
The first row is the one most often mishandled. Replacing the router with a more expensive one rarely extends coverage meaningfully, what's needed is an extra access point in the right place. The options are compared in the guide to mesh, repeaters, and access points.
If you do intend to replace the router, the considerations that genuinely matter are covered in the guide to choosing a Wi-Fi router.
Frequently asked questions
Is the box from my ISP a modem or a router?
Almost always both at once, and on a fibre subscription it also acts as the ONT. One box performs three jobs, which is exactly why the three terms get mixed up in everyday conversation.
Can I replace my ISP's router with a better one?
You can, but the ONT part usually can't be replaced because it's registered on the provider's network. The usual approach is to set the supplied device to bridge mode, then hand routing duties to a router of your choosing.
What is bridge mode?
A mode that makes the device stop acting as a router and simply pass the connection through to the device behind it. It's used when you want your own router to manage the network, without two layers of NAT complicating things.
If my Wi-Fi is weak, which one do I need to replace?
The router part, or more precisely the access point, not the modem or ONT. Neither of those affects wireless coverage inside the house.
