Modem vs Router vs Gateway: What Each Does and What You Need

Every home internet connection needs two jobs done. A modem (or, on fiber, a fiber terminal) connects you to your provider’s network. A router runs your home network: it lets all your devices share the one connection and usually provides your Wi-Fi. An ISP gateway is a single box that does both jobs.

So most homes need exactly one of each job: either a gateway on its own, or a modem or fiber terminal plus a router. The common mistake is ending up with two routers in a row, which this guide explains how to avoid.

The devices side by side

Each row is explained below.

• Wired (Ethernet)
• Wi-Fi

What a modem does

On cable internet, the modem speaks DOCSIS, the technology that carries broadband over cable networks. CableLabs, which develops DOCSIS, describes the cable modem as the network equipment that sits in the home, talking to the cable operator’s equipment at its hub site.

Fiber works differently but plays the same role. The provider installs a fiber terminal where the fiber enters your home, and your router plugs into it with an Ethernet cable. gFiber, for example, has customers connect the Ethernet port on its Fiber Jack to the router’s WAN (internet) port.

A modem or fiber terminal on its own gives you one connection. It doesn’t share that connection among devices or create Wi-Fi.

What a router does

The router is what turns one internet connection into a home network:

• It shares the connection. The router uses address translation (NAT) so that many devices with private addresses can share a single public internet address. Those private addresses, such as the familiar 192.168.x.x, are reserved for local networks and aren’t routed across the internet.
• It hands out addresses. Using DHCP, the router automatically gives each device that joins the network an address and its settings.
• It usually provides Wi-Fi. A “Wi-Fi router” is a router with a wireless access point built in, which is what most people mean by “router”.

What a gateway is

Using your own router

Many people add their own router for better Wi-Fi, coverage or features. How you do that depends on your equipment.

If you have a gateway, turn off its router so your own router is the only one. Providers usually call this bridge mode. Xfinity’s documentation describes it as turning off the gateway’s routing while leaving its modem on, so you can use your own router. It also lists the trade-offs: only one device can be connected to the gateway, and you lose the gateway’s network management and Xfinity’s Wi-Fi Extenders. Other providers use different names and steps, so check your provider’s documentation.

If you have a fiber terminal, you usually just plug your router into it. gFiber says bridge mode is only needed for some setups without a Fiber Jack. It also notes that its support covers the signal to the Fiber Jack, not the configuration of a third-party router.

The mistake to avoid: two routers in a row

If you plug your own router into a gateway that is still routing, each box translates addresses, so your devices sit behind two layers of NAT. This is called double NAT.

• Wired (Ethernet)
• Wi-Fi

Address translation is designed for connections your devices start: traditional NAT lets sessions go out from the private network, while sessions coming in are allowed only by exception, through fixed mappings.

Double NAT shows how to check whether you have it and the three ways to fix it.

Which setup do you need?

This is Router Academy’s guidance, based on the trade-offs above.

If you’re choosing your own router, How to choose a Wi-Fi router walks through the criteria, including matching its internet port to your plan. For how your Wi-Fi bands behave once it’s set up, see 2.4 GHz vs 5 GHz vs 6 GHz.