Many users are perplexed when a wireless network functions flawlessly, but a wired connection suddenly fails. This is a classic scenario, indicating a desynchronization of local interface settings or a physical defect in a specific data transmission channel. WiFi continues to work because it uses a different network adapter and, often, a different frequency band or communication channel within your equipment.
Unlike a wireless module, which automatically scans the air and selects parameters, wired connection Requires clear physical contact and proper speed matching between the computer's network card and the router port. If one of these elements is out of alignment, you'll see a connection icon with an exclamation point or a yellow triangle, even though the router itself is properly distributing traffic over the air.
Before panicking and calling a technician, it's worth understanding that the problem most often stems from trivial things: incorrect TCP/IP protocol settings, an outdated LAN port driver, or damaged cable insulation. Local area network (Ethernet) is considered more stable, but it is less forgiving of switching errors than WiFi, where packet retransmission is built into the communication standards.
In this article, we'll examine in detail all possible causes of wired internet failure when WiFi is working. You'll learn how to diagnose the physical integrity of twisted pair cables, check the status of network adapters in the operating system, and clear router configuration errors that specifically block LAN ports.
Physical diagnostics and cable condition
The first place to start (troubleshooting) is the physical layer. Ethernet cables (twisted pair) are much more susceptible to mechanical stress than radio waves. They could have been pinched by a table leg, bent at a sharp angle, or damaged by pets. Even if the cable appears intact, a loose connection in one of the eight wires could have occurred internally, which is critical for speeds above 10 Mbps.
Pay attention to the LED indicators next to the RJ-45 connector on your PC's network card and on the router port. They should normally be lit or blinking green/orange. If the indicators on both ends of the cable are not lit when the equipment is turned on, this almost certainly indicates a broken wire or a faulty port. If the indicators are flashing, but there is no Internet, the problem is software.
A common cause is wear on the connector itself. The plastic clips on the plugs often break, preventing the cable from locking tightly into the socket. Even the slightest movement can cause the connection to break. It's also worth checking that the ports on your router are not reversed: the cable from your ISP should be in the correct port. WAN (or Internet), and the cable to the computer is in the port LAN (usually numbered 1-4).
⚠️ Attention: If you are using an older Category 3 or 4 cable (rare, but common in older homes), it may not support modern Gigabit Ethernet speeds, causing modern network cards to refuse to establish a connection, requiring you to manually reduce the speed to 10/100 Mbps in the adapter settings.
To quickly check the line's integrity, try connecting the cable to another device, such as a laptop or Smart TV. If the cable internet works there, the problem lies with your main computer's network card. If not, look for a defect in the cable or router settings.
Problems with drivers and network adapter
If the cable is physically intact and the indicators are lit, but there's no network access, there's likely a software issue. The operating system may be incorrectly detecting the network card or using a standard Microsoft driver that isn't compatible with your specific chipset. Realtek, Intel or Qualcomm Atheros. This often happens after Windows updates or resetting the BIOS settings.
You can check the driver status through the Device Manager. Click Win + R, enter devmgmt.msc and find the "Network Adapters" section. If there's a yellow exclamation mark next to your card's name or it's listed as "Unknown Device," you need to reinstall the driver. Since you don't have cable internet but WiFi works, you can download the latest driver from the motherboard manufacturer's website using a wireless connection.
It's also worth checking your power saving settings. Windows often tries to save power by shutting down the network card when it's idle, but then fails to wake it up properly. This results in connection drops or failure to establish a connection.
How to disable power saving for a network card
Open Device Manager -> Network Adapters -> Right-click on your adapter -> Properties -> "Power Management" tab -> Uncheck "Allow the computer to turn off this device to save power".
Another important aspect is the duplex mode. In the adapter properties, in the "Advanced" tab, find the parameter Speed & Duplex (Speed and Duplex). By default, it's set to "Auto Negotiation." Sometimes the automatic setting fails, and devices can't agree on a speed. Try setting the value manually. 100 Mbps Full Duplex or 1.0 Gbps Full DuplexIf the connection reappears after this, the cable is of poor quality and cannot handle the maximum speed, or the router port is unstable.
IP addressing and DNS conflicts
One of the most common reasons why WiFi works but the cable doesn't is an IP address conflict. On a home network, the DHCP server on the router is usually responsible for distributing addresses. However, if you previously used a static IP address for work or school, those settings may have been retained. When you connect the cable, the computer attempts to connect to a network with "foreign" coordinates that don't match the current subnet.
You need to make sure that in the protocol properties IPv4 Automatic address retrieval is enabled. To do this, go to Control Panel → Network and Internet → Network and Sharing Center, click on the local area connection, select "Properties", find Internet Protocol version 4 (TCP/IPv4) and check the settings.
If automatic DNS retrieval is enabled but there's no internet connection, there may be a problem with the DNS cache or DHCP lease. The system may be "remembering" an old address that's already taken by another device, or the ISP's DNS server isn't responding over the wired interface. In this case, resetting the TCP/IP stack may help.
☑️ Actions in case of IP conflict
To reset your network settings, open a command prompt (cmd) as administrator and run several commands in sequence. First, flush the DNS cache:
ipconfig /flushdnsThen reset Winsock and TCP/IP settings:
netsh winsock reset
netsh int ip reset
After running these commands, be sure to restart your computer. This will reset all network settings to factory defaults and often resolves the issue where the system gets stuck trying to obtain an address.
Router Settings: LAN vs. WAN
Many users make the mistake of connecting the ISP cable directly to their computer, bypassing the router, or, conversely, mixing up the ports. If your WiFi is working, your router is turned on and configured. The problem may be that your ISP binds access to the device's MAC address. When you switch from WiFi to a cable, the MAC address changes (the WiFi and LAN ports on your router or computer have different MAC addresses), and the ISP blocks access.
In some cases, MAC address cloning is required. If you previously connected to the internet directly on your computer and now have a router installed, you need to copy the MAC address of your PC's network card into the router settings. This is done in the router's web interface, usually in the "Settings" section. Network → MAC Address Clone.
It's also worth checking whether MAC address filtering is enabled on the router's LAN ports. While this setting is rare for home networks, in office environments, administrators may restrict access to trusted devices only. If you've changed your computer or network card, the new MAC address may be blocked by security rules.
Don't forget about your connection type. If your ISP uses PPPoE (requires a login and password), then when connecting through a router, these settings must be entered into the router itself. If you connect the ISP cable directly to your PC, you need to create a connection through "Network Settings." An incorrect connection type will result in a physical connection but no access to the global network.
Comparison of WiFi and Ethernet diagnostics
Understanding the differences between wireless and wired connections helps you quickly find the root of the problem. WiFi is more flexible and forgiving of configuration errors, automatically switching between channels. Ethernet requires strict adherence to protocols. Below is a table to help you isolate the problem.
| Parameter | WiFi (Wireless) | Ethernet (Cable) | What does this mean for you? |
|---|---|---|---|
| Physical level | Radio waves, antennas | Copper wires, connectors | Check the integrity of the cable and latches |
| Indication | Tray icon, signal level | LEDs on the port (Link/Act) | No light on the port = open or burnt out port |
| Driver dependency | High (requires your own module) | Average (basic ones often work) | Update your LAN card driver separately from your WiFi driver. |
| The influence of interference | High (microwaves, neighbors) | Minimal (electromagnetic interference only) | The cable should not be located near 220V power wiring. |
As the table shows, if the WiFi is working, then the router itself and the line to the ISP are working. This narrows the search to the "Router - Cable - Computer" section.
Provider-side failures and technical work
Sometimes the reason is as simple as: your provider is performing maintenance on the node that serves your home via FTTB (fiber-to-the-building) technology, which involves wiring apartments via Ethernet cables. In this case, WiFi may work through a 4G modem built into the router, or because the provider uses different access channels for different technologies.
It's worth calling technical support and checking if there are any outages in your area. The operator can also see that your port on the switch in your entryway is constantly generating CRC errors, indicating a faulty cable, and block the port remotely to prevent any impact on the overall network.
⚠️ Attention: Tariff plan terms and network capabilities are subject to change. Some providers limit the number of devices connected via cable or require a separate fee for a static IP address. Please check your current contract terms in your personal account.
If your ISP confirms the line is clear and the WAN indicator on the router is lit, but there's no LAN internet, the router may need a firmware update. Firmware errors (bugs) can cause LAN ports to freeze while the WiFi module continues to function. Resetting the router to factory settings (press the "Reset" button) Reset) often helps to solve such logical errors.
Frequently Asked Questions (FAQ)
Why is the LAN port indicator orange instead of green?
An orange light usually means a connection has been established, but at 10/100 Mbps, not 1 Gbps. This could be a sign of poor cable quality (not all eight wires are making contact) or power saving settings. If the speed is acceptable, this isn't a critical error.
Can an antivirus block internet access via cable?
Yes, some antivirus programs and firewalls have a "Home Network Protection" or "Public Network Mode" feature. When connecting a new cable, Windows may detect the network as "Public" and deny access, even though an exception has already been made for the WiFi profile. Check your firewall settings.
What should I do if the cable is intact, the drivers are installed, but there is no internet?
Try replacing the port on your router. Switch the cable from LAN1 to LAN2. Often, one port can fail due to a power surge or physical wear and tear, while the others are working properly.
Does cable length affect internet availability?
The Ethernet standard (twisted pair) guarantees stable operation over distances of up to 100 meters. If your cable is longer, the signal will weaken and the connection will fail. Cable category is also important: for gigabit speeds, a minimum Cat5e cable, installed properly, is required.
Do I need to reboot my router if my cable internet connection is lost?
Yes, this is the first step. A router is a mini-computer, and its DHCP server or switch can freeze. Rebooting clears the device's RAM and restarts the address distribution process for all connected ports.