This is an interesting question. We often have spare routers lying around, and it’s common to wonder whether a router is any use on it’s own. Does a router need to be connected to a modem in order to work?

The answer depends on what you are planning to use the router for, but here is a summary answer:

In order to access the internet, a router must be connected to a modem. However, it is possible to transfer data between devices over local networks using only a router. Therefore, a router does not strictly need to be connected to a modem to function, but it must be for it’s most common use of facilitating internet access.

In other words, a router almost always is connected to a modem, but doesn’t technically need to be for more specialized uses like creating LAN networks.

Let’s look at the different ways of using a router in more detail, and see how they relate to modems.

A Router Must Be Connected To A Modem To Access The Internet

By far the most common use for a router is to allow devices to access the internet and get online, and for this purpose, a router must be connected to a modem to work.

To understand why routers need modems to access the internet, let’s look at some of the key differences between routers and modems:

Modems:

• Modems effectively take the data that comes into your home from the wider internet (0’s and 1’s) and convert it into a usable form for devices to decipher.
• Modems communicate with your ISP, and therefore any modem used must be compatible with the type of connection (DSL/cable etc) and with the ISP.
• Modems typically do have one ethernet port on the back, which could be used to connect up one device via LAN cable, but this is usually used to connect up to the router which then typically provides 4 ethernet ports plus Wi-Fi access for better connectivity.
• Modems do not set up or manage home networks, nor do they broadcast any Wi-Fi. They purely decode data from the internet, which is then sent to the router to be distributed to the correct device on the network.
• See below for an example of a standalone ADSL modem:

Routers:

• Routers are essentially devices for creating and managing home networks.
• They are also acting as intermediary devices between devices and the broader internet.
• They provide typically 4 LAN access points to plug devices into, and also broadcast one or more wireless networks for devices to connect to via Wi-Fi. Hence, routers will often have antenna, while standalone modems won’t.
• They assign IP addresses (unique identifiers) to devices to allow more effective management of home networks.
• They provide firewall and other extra security measures for the home network, so data is not coming straight off the internet unfiltered and unchecked.
• Routers are an essential part of any home network where multiple devices are connecting. If you had just a modem, you could only connect one device maximum, and by cable only. Routers allow access for more devices. However, they cannot get online without modems.

In other words, routers and modems complement each other and both are necessary to facilitate internet access. You can use a modem without a router (in a very limited fashion), but you cannot get online just using a router without a modem.

Combined Modem Routers vs Standalone Routers

The picture though is somewhat complicated by the fact that sometimes routers and modems are bundled into one (a combined modem-router – for newer fiber services), or sometimes there’s a standalone router that’s connected to a separate modem (for older style ADSL/VDSL internet services).

Let’s clarify the different scenarios here:

Scenario #1 – Combined Router Modem – In many cases, what is casually referred to as a “router” or “Wi-Fi router” is actually a combined router-modem, with the modem being contained within the same device as the ethernet ports and Wi-Fi router. This is the case with most newly supplied ISP “routers” nowadays; they have both the modem and router built in, often referred to as “Wi-Fi/wireless hub/box/station”, or something similar.

Here’s mine:

It will usually be a black or white box of some kind, with no other separate modem connected to it. It just goes straight into the phone line/master socket/installation panel with an RJ-11 cable, and this gets you online as long as you have a live internet service installed.

Here are some things to look for here:

• The combined router-modem goes straight into the wall with no devices in between
• The port on the back is often called the DSL/ADSL/Internet/Fiber/Broadband port
• The cable coming out of this port is an RJ-11 cable, which looks similar to a standard RJ-45 ethernet cable, but the connector is very slightly smaller and squarer.

Scenario #2 – Standalone router and separate modem – Now let’s cover the slightly less common case nowadays of having the modem and router separate. In this case, you’ll have two separate devices that need to be connected. The router is connected to the LAN port on the modem, and the modem then goes into the phone line/master socket to connect you to the wider internet.

Here’s an example of a separate modem (on the left) and router (on the right):

Here are some things to look out for here:

• A standalone router will go into a separate modem with an RJ-45 ethernet cable, and the modem then goes out to the phone line with an RJ-11 cable.
• The port that goes out to the modem is often called the WAN port (sometimes also called Internet though) on standalone routers, and is an RJ-45 ethernet port just like the LAN ports, not the slightly smaller RJ-11 cable that it is on combined modem-routers.
• It’s often set up like this on older or slower speed DSL/ADSL/VDSL internet services.

However, regardless of whether the router and modem are combined or separate, the router still somehow needs to be connected to the modem in order to allows devices to access the internet. It can’t get online on it’s own without a modem.

Routers Can Transfer Data Over Local Networks Without a Modem

However, now let’s look at the case when a router can still serve a function without needing a modem. Most commonly, this is in local networks (LANs), where they can facilitate data transfer between devices on a network without needing to be connected to the internet via a modem.

Perhaps the best example of this would be a LAN Party, when multiple gamers gather together in one place and connect their gaming devices directly and locally rather than over the internet. Depending on the numbers of gamers, a router or a switch will be used to connect all the devices together, and as long as all gaming is done over the local network, with no internet access required, there shouldn’t be any need for a modem.

The router/switch would act as a middle-man in this scenario, with all devices connecting to the LAN ports on the router, which then transfers data between them all so the gaming can take place.

This is a much rarer use for a router, but in this particular case, it can work on it’s own with needing to be connected to a modem.

A router could also be used as a middleman to facilitate the transfer of data between other devices on a network (eg. sending files between 2 PC’s). However, in the modern era, this often isn’t necessary with file sharing options often allowing the direct transfer of data between devices without even needing a router.

So here’s a bottom line answer:

As a general rule, routers can transfer data over local networks without needing a modem. However, routers cannot send or receive data over the wider internet without being connected to a modem.