Two different faults: no connection, or a slow link
When a computer, games console or TV plugged into the router with an Ethernet cable (the network lead with a clip on each plug) misbehaves, it usually shows one of two symptoms:
- No connection at all. The device doesn't see a network, or sees one but can't reach the internet.
- A capped connection. It works, but reports a link speed of 100Mbps when the router port and the device can both do 1Gbps.
The link speed is the speed the device's network adapter agreed with whatever it's plugged into: Intel's support pages call it the negotiated connection speed. It isn't your broadband speed, and a working gigabit link reads 1.0Gbps even on a slower package. But it sets the ceiling for that device, so a link stuck at 100Mbps holds back a faster line.
Both faults are usually physical, so this guide works from the plugs outwards, then looks at the computer's settings, then at anything between the router and the device.
First, is it the cable or the whole connection?
First check whether the broadband itself is working. Microsoft's Ethernet troubleshooting suggests connecting the same computer over Wi-Fi, if the router has it, to narrow down where the problem is. It also suggests trying another computer on the same connection: if that one connects, the problem is likely the first computer; if neither connects, Microsoft says it might be the router, your provider, or a USB to Ethernet adapter if you're using one.
- Wi-Fi devices are fine, the wired one isn't: the fault is somewhere on the wired path or in that computer. Carry on below.
- Nothing in the house can get online: the cable to one device isn't the problem. Check the hub, and on full fibre the cable between the router and the fibre box (see Step 1), then see what to do when your broadband is down.
- Everything drops out from time to time, Wi-Fi devices included: that isn't the Ethernet lead to one device. See why broadband keeps dropping out.
- Only the wired device drops out: treat it as a wired fault and start with the plugs below.
Step 1: the plugs, the cable and the port
- Push both plugs in until they click. BT says you'll hear a click as the connections lock into place. Intel goes further: a plug that won't click should be treated as broken and the cable replaced.
- Use a LAN port, not the Internet port. Microsoft's advice is to use one of the router's Ethernet ports, not the Internet port that connects the router to the modem. LAN stands for local area network: your home network. The Internet port may be labelled WAN or Internet.
- Try a different cable. Microsoft says that if a second cable works, the first one may be the problem.
- Try a different port on the router. Intel's advice is to power-cycle the router or switch and try other ports on it.
- Read the cable's category. It's printed on the outer sheath, usually near each end, as “Cat” and a number.
BT's own Ethernet cables are generally yellow, or white with yellow ends. Cables bought elsewhere can be any colour, so go by the printing, not the colour.
Openreach full fibre: two Ethernet cables, two different jobs
On Openreach full fibre the fibre comes into a small wall box called an ONT (optical network terminal). Openreach explains that its ONT is not a router: your router connects to the ONT's Ethernet port, sometimes labelled LAN or Data, from the router's WAN or internet port. So one Ethernet cable is your broadband connection and the others carry your devices. If you're not sure which ports to use, Openreach says your provider's set-up guide will show you. Other full fibre networks may set things up differently, so go by your own provider's instructions.
- BT customers: BT says the cable with red ends goes from the Hub's WAN port (or port 4) to the Openreach modem's PORT1 or LAN1. If yours is in port 4, that port is taken, so plug devices into the others. A replacement should be Cat5e or higher, BT says.
- Don't touch the fibre. BT tells customers not to unplug the green optical cable, and Openreach says removing or tampering with its box could interrupt your connection and could lead to a call-out charge.
Our explainer on the ONT and your router shows how the pieces fit together.
Step 2: read the lights
Light meanings vary between makers and models, so go by what your own provider or equipment maker publishes. Here's what the sources we checked say (October 2026), with our own reading in the last column:
Where | What the maker says | What to do next |
|---|---|---|
Network socket on the computer | BT: if no Ethernet icon appears, check for flashing green lights where the cable goes into the computer | If there are none, suspect the cable, the port or the adapter first. Not every adapter has lights, so a dark socket isn't proof on its own |
BT Hub main light | BT: if you can't get online, make sure the Hub's main light is blue (blue means the Hub is connected to your broadband) | If it isn't blue, check BT's light guide before blaming the cable |
BT Smart Hub 2, flashing purple | BT: the Hub is working but the broadband cable isn't connected | On full fibre, check the red-ended cable at both ends |
Openreach modem PORT lights (BT full fibre) | BT: status lights should be steady green; if PORT 1 gives no internet, try the next port along | If the PORT light is off or flashing and problems continue, BT says to contact it |
Network switch ports | TP-Link's TL-SG108 switch has a Link/Act light built into each port | If a port's light stays off with a device plugged in, check that cable and device first |
For other providers' hubs, see their help pages or our guide to what broadband hub lights mean.
Step 3: check what the computer thinks
If the cable is in, the lights are on and the hub is online, the next suspect is the computer: its settings, its network adapter, or its driver (the small piece of software that lets the operating system talk to the adapter).
On Windows
Microsoft's page on fixing Ethernet problems (checked October 2026) runs in this order. Stop when the connection comes back:
- Run the troubleshooter. On Windows 11, Microsoft says to start with the Network and Internet troubleshooter in the Get Help app. On Windows 10 it's under Settings > Network and Internet > Status > Network troubleshooter.
- On the router: check the cable, then restart. After the cable and port checks in Step 1, unplug the router, then the modem, wait at least 30 seconds, plug the modem in and let its lights stop blinking, then plug the router in and give it a few minutes. If they're one box, restart it once.
- On the PC: check the status. In Windows 11, open Settings > Network & internet. The Ethernet status at the top should say Connected. If it shows an error such as Action needed, select Ethernet to see the settings.
- Try Wi-Fi instead, which both gets you online and narrows down the fault, as above.
- Run the network commands. Microsoft lists five commands to type into Command Prompt run as administrator, which reset the network software, renew the address the router gave the PC and clear its DNS cache. Our guide to being connected with no internet lists them.
- Uninstall the adapter driver. In Device Manager, under Network adapters, uninstall the Ethernet adapter and restart so Windows reinstalls it. Microsoft suggests this especially if the problem began after an update, and says to download the latest driver from your PC maker's website first as a backup.
- Network reset, last. Under Settings > Network & internet > Advanced network settings, this removes and reinstalls all network adapters with default settings. Microsoft warns you may need to reinstall VPN software afterwards, and that your networks may be set to a public profile, which hides the PC from other devices at home.
- Try another PC on the same cable, as in the first check above.
Settings you changed by hand
If someone once typed a fixed IP address or a different DNS server (the service that turns web addresses into numbers) into the device, perhaps for a game or a work tool, that can stop it getting online. BT says that if you've manually changed settings such as the IP address or DNS server, you might need to change them back to automatic. If a device genuinely needs a fixed address, our guide to giving a home device a fixed IP address explains how to reserve one on the router instead.
Connected, but stuck at 100Mbps
Everything works, but downloads never pass about 100Mbps on a faster line: the device has linked at 100Mbps instead of 1Gbps.
Seeing the link speed on Windows. Intel's support article (written for its Killer adapters, last reviewed in 2021) shows it in Control Panel > Network and Internet > View network status and tasks: click the Ethernet connection and read the Speed. Intel says a working gigabit link reads 1.0Gbps.
Leave the adapter on automatic. Intel says the adapter's Speed & Duplex setting (Device Manager, the adapter's Properties, Advanced tab) should be Auto Negotiation, the default. If it is and the link still reads 100Mbps, Intel says the issue is “almost always” an Ethernet cable, though it could be a few things, and that a gigabit adapter reporting 100Mbps is almost certainly a physical problem with the networking equipment.
The usual causes
- A damaged cable. Intel says a failed Cat5e or Cat6 cable will usually still work at 100Mbps, so damage can show up as “slow” rather than “broken”. Its examples: running over the cable with an office chair, stepping on it or shutting a door on it can make a Cat5e cable drop to 100Mbps. Replace any lead that's been trapped or pinched; Intel prefers Cat6 to Cat5e for the replacement.
- An old or unmarked cable. ISPreview's rough guide puts plain Cat5 at 100Mbps, so a lead marked Cat5 with no “e”, or with worn-off printing, is worth swapping first.
- A router power-saving setting. ISPreview warns that some routers have an Ethernet power-saving option that can hold gigabit ports to around 100Mbps.
Our guide to why one device is slower than the rest goes into cable categories, that router setting and device limits in more detail.
On a Mac
Apple says Gigabit Ethernet needs a cable that supports it. If the Mac and the router support it but the cable doesn't, Apple says you may need to set the speed by hand or buy a Gigabit-capable cable. The manual setting is under System Settings > Network > Ethernet > Details > Hardware, but Apple's caution is to use automatic settings unless your network administrator has given you specific ones, because the wrong settings can affect performance.
The bypass test
Intel's most useful step is an isolation test. Connect the computer directly to the router (Intel's article says modem) with one cable you know is good; Intel suggests Cat6 or better. If the link now reads 1.0Gbps, the problem was in whatever you bypassed: a wall socket, a switch, an extra cable or a powerline adapter. If it still reads 100Mbps with a good cable and different router ports, Intel says the Ethernet connector on the computer itself likely has an issue.
Change one thing at a time and note the link speed after each change, so you know which part made the difference.
Switches and powerline adapters in between
Once the bypass test has pointed at a box in between, check it.
Network switches. A simple switch, such as TP-Link's TL-SG108, senses the speed of each device plugged into it and has a light on each port. So if one device behind a switch links at 100Mbps while the others link at gigabit, suspect that device's cable or port. If everything behind it is slow, check the cable back to the router and the switch's own port speeds, and power-cycle it as Intel suggests. Our guide to wiring your home with Ethernet covers choosing and connecting a switch.
Powerline adapters
Powerline adapters carry the network through your home's electrical wiring, and TP-Link says they work in sets of two or more on the same electrical circuit.
- Wall sockets only. BT and TP-Link both say to plug them straight into a wall socket, not an extension lead or power strip, which may filter the signal. BT found that pricier anti-surge strips with EMI/RFI filters (filters against electrical noise) were more likely to stop adapters working than basic ones.
- One cable per device. BT says to connect only one Ethernet cable between each device and its adapter; more won't help and may stop it working.
- The side-by-side test. BT says that if the adapters work next to each other but not in their usual rooms, your home's electrical wiring may be affecting the connection.
BT's Mini Connectors (checked October 2026) show an Ethernet light that's solid blue when connected and transferring data, and off when no Ethernet connection is detected. Their Data light is blue for excellent, orange for good and red for poor, and off when there's no connection between the adapters or they're asleep. If there are no lights at all, BT's checks are: make sure the wall socket is switched on, try another socket, check the Ethernet cables are firmly in, unplug for 30 seconds and plug back in, and test the socket with another appliance. If the socket works and there are still no lights, BT says the adapter may be faulty.
Other makes use their own lights. If drop-outs follow a pattern through the day, see our guide to electrical interference and broadband.
Test the connection once it's fixed
Ofcom's consumer guidance on broadband speeds advises that the most accurate speed test uses a computer or tablet connected to the router by an Ethernet cable, because Wi-Fi can slow the signal down. With the cable sorted:
- Plug the computer into a router LAN port with the known-good cable, and pause other heavy use if you can.
- Run our broadband speed test and note the result.
- Test again in the device's usual spot, through any switch or powerline adapter. A big gap points to the box in between, not the line.
Different testers can give different numbers, as our guide to why speed tests give different results explains. On a gigabit package, a wired result a little under 1,000Mbps isn't a fault; our guide to home networks faster than 1Gbps explains why, and what you'd need for more.
When it isn't your cable
If two good cables, two router ports and a second computer all fail, Microsoft says the problem might be the router, your provider or a USB to Ethernet adapter. Check the hub is online using your provider's light guide (on a BT Hub, the main light should be blue), check the cable to the fibre box on full fibre, and report the fault to your provider if the hub can't get online.
Questions worth asking your provider, especially before an upgrade:
- How many Ethernet ports does the router have, and what speed are they?
- Does it have an Ethernet power-saving setting, and can I turn it off?
- On a package faster than 1Gbps, which port gives one device the full speed?
If your wired test at the router is fine but the line isn't fast enough for your household, no cable will fix that. You can compare deals at your postcode through our comparison partner, look at fibre broadband deals, or browse the broadband providers, such as BT and Virgin Media. We compare deals; we don't switch you or give personal advice, so check router and port details with the provider before you sign up.
Ethernet connection FAQs
Why does my Ethernet cable say connected but there's no internet?
First check whether other devices can get online. If nothing in the house can, look at the hub and the line (and on full fibre, the cable to the fibre box) rather than this cable. If only the wired device is stuck, check nobody set a fixed IP address or DNS server on it by hand (BT says to set them back to automatic), then work through Microsoft's steps: the troubleshooter, a modem and router restart, the network commands, the adapter driver and, last, a network reset.
Why is my wired connection stuck at 100Mbps?
Intel's article (written for its Killer adapters) says that if the adapter's Speed & Duplex setting is on Auto Negotiation and it still links at 100Mbps, the cause is almost always the Ethernet cable, though it could be a few things. A damaged Cat5e or Cat6 cable often keeps working at 100Mbps, and ISPreview's rough guide puts plain Cat5 at 100Mbps. Try a known-good Cat5e or better cable straight to the router, and check for an Ethernet power-saving mode on the router.
Which Ethernet cable do I need for gigabit broadband?
As a rough guide from ISPreview, Cat5e and Cat6 both handle 1Gbps, while plain Cat5 is rated for 100Mbps. For a BT full fibre Hub-to-modem cable, BT asks for Cat5e or higher, and Intel prefers Cat6 to Cat5e. For speeds above 1Gbps, see our guide to multi-gigabit home networks.
Can I plug my computer straight into the full fibre box?
No, not on Openreach full fibre. Openreach says its ONT is not a router: it connects to your broadband router's WAN or internet port, and your devices then connect to the router. Leave the ONT and its green optical cable alone. Openreach says removing or tampering with it could interrupt your connection and could lead to a call-out charge.
Why do my powerline adapters show a red light?
On BT's Mini Connectors, a red Data light means a poor connection between the adapters. BT suggests plugging them straight into wall sockets, removing extension leads and surge-protected adaptors, trying different sockets, checking the cables and restarting both. If they work side by side but not in their usual rooms, BT says your home's wiring may be the cause. Other makes have their own light meanings.
Does a network switch slow down my wired connection?
A switch with 10/100/1000Mbps ports, like TP-Link's TL-SG108, senses the speed of each device on each port, so a gigabit device can still link at gigabit through it. Intel's test is to bypass the switch with one known-good cable straight from the router: if the link improves, the switch or its cabling is at fault.
