Why is my computer's internet connection slow through a router, but Wi-Fi works fine?

It's puzzling when a smartphone or tablet has excellent wireless speeds, while a desktop computer connected to the same router barely loads pages. Users often assume the problem lies with their ISP, even though the local network is functioning properly. In reality, the root cause often lies in the physical connection or software conflicts at the operating system level.

Unlike a wireless protocol, which takes care of some of the signal optimization calculations, a wired connection requires perfect line integrity. Even the slightest cable damage or malfunction network card may cause throughput to drop to minimal values. It's important to understand that Wi-Fi and LAN ports use different hardware modules within the router.

In this article, we'll conduct a thorough diagnostic of your hardware. We'll examine hidden driver settings, check the quality of twisted pair cable crimping, and rule out Windows software errors. There is no magic here., only the consistent elimination of bottlenecks that interfere with normal data exchange.

Physical issues: cables and ports

The most common, but often ignored, reason is the condition of the cable. EthernetUnlike Wi-Fi, where the signal is transmitted over the air and dynamically adapts to interference, a wired channel requires the physical integrity of all eight wires. If the cable is pinched, severely bent, or has a poor connection at the connector, the network card may drop speeds from 1 Gbps to 10 or 100 Mbps.

Pay attention to the LAN port indicators on the motherboard and router. They typically light green for high speeds and yellow (or orange) for low speeds. If you see a yellow light, this is a clear sign of problems with the physical level connections. It's also worth checking the connector itself: if the plastic clips are broken, the cable may come loose with the slightest movement.

⚠️ Caution: Do not use cables marked CAT3 or CAT5 without index if your plan exceeds 100 Mbps. For modern speeds, you need a standard cable CAT5e or CAT6.

Often, the problem can be solved by simply replacing the patch cord. Even if the old cable appears intact, one of the wires may have broken internally, causing the network adapter to go into emergency mode. Try connecting your computer to the router with a short, known-good cable to rule this out.

Network card drivers and Windows settings

If the cable is OK, we move on to the software part. The Windows operating system may not correctly manage the network card's power saving. In an attempt to save power, the system may switch to network adapter into sleep mode or limit its performance, which leads to unstable ping and low speed.

To check, you need to go to the Device Manager. Press the key combination Win + X and select the appropriate item in the menu. Find the "Network adapters" section, right-click on your controller (usually it's Realtek, Intel or Killer) and select "Properties". On the "Advanced" tab, look for options related to Energy Efficient Ethernet or Green Ethernet, and try to disable them.

Having up-to-date drivers is also critical. Standard Windows drivers often perform poorly with modern gigabit cards. It's recommended to download the latest software from the official website of your motherboard or laptop manufacturer. An outdated driver may not be able to properly handle large volumes of traffic, creating packet queues.

IP and DNS conflict

Sometimes a computer receives incorrect network settings. If another device on your local network has the same static IP address, a conflict will occur, and the internet on your PC will work intermittently or not work at all. Wi-Fi devices may receive addresses from a different range or pool, so the issue doesn't affect them.

You can check your current settings via the command line. Enter the command ipconfig /all and pay attention to the lines "IP address" and "Default gateway". If the address starts with 169.254.x.x, this means the computer was unable to receive settings from the router automatically. In this case, you need to reset the network settings.

To reset, open a command prompt as administrator and enter the following commands one by one:

netsh winsock reset
netsh int ip reset
ipconfig /release
ipconfig /renew
ipconfig /flushdns

After executing these commands, the computer will rewrite the network stack and request fresh data from the router. This often solves problems with DNS servers, which can respond slowly to requests, creating the illusion of a slow internet connection.

Router restrictions and traffic prioritization

Modern routers have intelligent traffic distribution features known as QoS (Quality of Service). Your router's settings may prioritize wireless devices or specific applications. In this case, the router is deliberately throttling the wired connection, favoring Wi-Fi clients.

Go to the router's web interface (usually at 192.168.0.1 or 192.168.1.1). Find the section related to QoS, Bandwidth Control, or Traffic Manager. Check if there's a speed limit (Limit) for your computer's MAC address. Also, make sure "Wi-Fi First" or a similar feature that prioritizes wireless over wired networks isn't enabled.

⚠️ Note: Router interfaces from different manufacturers (Asus, TP-Link, Keenetic) vary significantly. If you're unsure of what you're doing, it's best to reset your router to factory settings to rule out software configuration errors.

Furthermore, older router models may have weak processor power. When actively downloading torrents to a PC, the router's processor may struggle to process NAT tables for the wired interface, while the Wi-Fi module, which has its own firmware, continues to operate more reliably.

Comparison of Features: LAN vs. Wi-Fi

To better understand the nature of the problem, let's compare the technical features of both connection types. Users often forget that even with the same advertised speed, actual throughput can vary due to duplex and loss.

As the table shows, a wired connection should, in theory, be more stable. If Wi-Fi performs better, this almost always indicates a faulty LAN port or cable, as under ideal conditions, a cable outperforms air in all reliability parameters.

Why can Wi-Fi be faster than old cable?

If your cable is rated CAT5 (without the "e") and has 4 wires instead of 8, it is physically limited to 100 Mbps. Modern Wi-Fi 5 (AC) or Wi-Fi 6 (AX) easily delivers speeds above 300-400 Mbps, so the wireless connection in this case will be faster.

The impact of antiviruses and firewalls

Don't discount the software installed on your computer itself. Third-party antiviruses and firewalls often have "Network Protection" modules that scan all incoming and outgoing traffic in real time. On slower PCs, this can create a bottleneck, especially on gigabit connections.

Try temporarily disabling your antivirus and Windows Firewall. If the speed immediately improves, the problem lies in your packet filtering settings. You might find a "Scan secure connections" option or something similar in your antivirus settings. Disabling it often restores normal speeds without compromising overall security.

Also, check for background processes running that you don't notice. Steam, Epic Games, torrents, or cloud storage can consume all your bandwidth, leaving only a fraction of it for your browser. Open Task Manager (Ctrl + Shift + Esc), go to the "Performance" -> "Ethernet" tab and see which process is loading the network.

Detailed diagnostics via the command line

Advanced users might find it helpful to run a packet loss test. This will help them determine where exactly data is being lost: on the way from the PC to the router or further out to the external network. Launch the command prompt and enter the following command:

ping 8.8.8.8 -t

Monitor the response time (time). Normally, a wired connection should be stable, for example, 1-3 ms to the router and 10-20 ms to the external server. If you see spikes up to 100-200 ms or "Timeout exceeded" messages, this indicates a problem.

Compare these metrics with the ping results on a device connected via Wi-Fi. If the ping is stable on Wi-Fi but fluctuates on a cable connection, the problem is localized within your apartment (the cable, the PC port, or the router port). If the ping is poor everywhere, the problem lies with your ISP or the router itself.

⚠️ Important: When running speed tests, disable VPNs and proxy servers. They can significantly lower actual speeds and increase ping, creating the false impression of hardware failure.

Use the utility tracert (trace) to see the path of the packet. The command tracert 8.8.8.8 will show all nodes. The first node is your router. If latency appears already at the first step, look for the problem in the computer or cable.

When is it time to replace equipment?

Sometimes software solutions don't help, and you have to admit the physical death of your hardware. Network cards, especially those integrated into budget motherboards, are sensitive to power surges. If a LAN port is partially burned out, it may detect the cable but won't be able to maintain high speeds.

In this case, there are two options: buy a USB network card (USB to Ethernet adapter) or replace the router with a model with higher-quality components. An external adapter is often more stable than an integrated one, as it has its own cooling system and is not dependent on the motherboard chipset.

You should also consider replacing your router if it's more than 5-7 years old. Technology evolves rapidly, and older devices may not be able to handle modern encryption protocols and high speeds, especially with multiple connected clients.

Why is the speed limited to 100 Mbps, although the tariff is 500?

This is a classic sign of using a CAT5 cable with four active conductors instead of eight. For speeds above 100 Mbps (the Gigabit Ethernet standard), all eight conductors must be intact and connected. Check the connectors for tightness or replace the cable with a CAT5e/CAT6 cable.

Can a virus slow down the Internet only on a computer?

Yes, absolutely. Mining viruses or botnets can use your network resources to send spam or mine cryptocurrency, consuming 100% of your bandwidth. Scan your computer with an antivirus and network activity monitor.

Should I disable IPv6 to speed things up?

In some cases, ISPs incorrectly route IPv6 traffic, leading to long connection timeouts. Disabling IPv6 in your network adapter properties can speed up webpage loading if your ISP doesn't fully support it.

How to check if the network card is overheating?

Windows typically doesn't have a direct temperature sensor for LAN. However, if speed drops after 10-15 minutes of active loading and then recovers after idle time, this may indicate thermal throttling of the network chip or router. Improve ventilation of the system unit.