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A modem connects your house to your provider. A router shares that one connection among your devices and provides Wi-Fi. A gateway is both in one box. That distinction sounds pedantic and is actually the key to several problems on this site, because only the modem has to live where the cable enters.
What each one does
Modem
Router
Gateway
Job
Translates the provider's signal into Ethernet
Shares one connection among many devices
Both
Talks to
Your provider's network
Your devices
Both
Provides Wi-Fi
No
Yes
Yes
Has to sit where the line enters
Yes
No
Yes
Changes when
Your provider's technology changes
Wi-Fi standards change
Either, so both
On fiber
Replaced by the ONT, supplied by the provider
Still needed
Sometimes required (AT&T)
Scroll the table sideways to see every column.
The modem, in more detail
On cable, the modem converts the radio-frequency signal on the coax into Ethernet. Its capability is dictated by your provider's DOCSIS generation — which is why modem choice is an approved-list question rather than a performance one. On fiber, this job is done by the ONT, which is provider-supplied and not something you buy.
The router, in more detail
The router assigns each device a local address, decides where traffic goes, runs the firewall, and provides the Wi-Fi. This is the half that determines what your network feels like, and the half that Wi-Fi standards keep moving.
Try this first
This is why separates beat a combo: only the modem is stuck by the wall
The coax or fiber enters wherever the installer found it convenient, which is usually a corner, a garage or a utility closet — the worst possible place for a radio. With separates, the modem stays there and the router goes somewhere central over a single Ethernet run (or a MoCA link over existing coax). That is frequently the single largest free-or-cheap improvement available to a household. See where to put your router.
Bridge mode, and why it matters
If you keep your provider's gateway and plug your own router into it, you now have two routers in series. Both hand out private addresses, which is called double NAT, and it breaks port forwarding, some games, some VPNs and some smart-home remote access while adding latency for no benefit.
The fix is to put the gateway into bridge mode, which turns off its routing and Wi-Fi and reduces it to a modem. On AT&T Fiber the equivalent is IP passthrough, because the gateway cannot be removed — the AT&T page covers it. Either way, also turn the gateway's Wi-Fi off so its radios stop competing with your router's.
Which one should you replace?
Wi-Fi is slow everywhere including next to the box — the router half. See do you need a new router.
Wired speed is well below your plan — the modem half, especially if it is DOCSIS 3.0 or has only Gigabit ports on a multi-gig plan.
You are paying an equipment fee — whichever half the fee is for. The arithmetic is on the provider pages.
Coverage is bad in far rooms — neither. That is a coverage problem and needs an extra radio, not a better box.
Quick picks
Ranked by our published scoring rubric (does its job, flexibility, longevity, value). Tap any row to jump to the full write-up, or go straight to the retailer from the right-hand column. How we score.
#
Product
Best for
Score
Price
1
Illustrative
ARRIS SURFboard S33DOCSIS 3.1 with a 2.5 Gbps port and approval across Xfinity, Spectrum and Cox. Pair it with any router you like.
Scroll the table sideways on a narrow screen. Scores are our editorial assessment from published specifications and independent testing by named outlets — not our own lab results. What we do and do not test.
The picks in full
Illustrative
#1 · The modem half, on cable
ARRIS SURFboard S33
ARRIS · Midrange
The SB8200's replacement in practice: same broad approval, plus a 2.5 Gbps port so it can keep up with a faster plan later.
Key specifications
Standard
DOCSIS 3.1
Ports
2.5 Gbps plus Gigabit Ethernet
Approved by
Xfinity, Spectrum, Cox and most cable ISPs
Score 9.4/10
Does its job9.5
Flexibility10.0
Longevity9.5
Value8.5
What it gets right
+The 2.5 Gbps port means the modem will not be the thing capping you after a plan upgrade
+Approved almost everywhere, so it moves house with you
What to watch for
−Costs more than the SB8200 for headroom you may not use yet
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Common questions
What is the difference between a modem and a router?+−
A modem connects your house to your provider and converts their signal into Ethernet. A router shares that single connection among your devices, runs the firewall and provides Wi-Fi. A gateway combines both in one box.
Do I need both a modem and a router?+−
You need both functions. On cable that means either a gateway or a separate modem and router. On fiber the provider's ONT does the modem job, so you only add a router. Separates are generally better because only the modem has to sit where the line enters.
What is bridge mode and do I need it?+−
Bridge mode turns off a gateway's routing and Wi-Fi so it behaves purely as a modem. You need it whenever you put your own router behind a provider-supplied gateway — otherwise you get double NAT, which breaks port forwarding, some games and some VPNs.
Can I put my router somewhere other than where the cable comes in?+−
Yes, and you usually should. Leave the modem at the entry point and run one Ethernet cable — or a MoCA link over existing coax — to a central spot for the router. It is one of the largest cheap improvements available.
Illustrative
