Troubleshooting Ethernet Speed Limitations: When Your LAN Connection Is Stuck at 100 Mbps
Recently, many users have encountered a perplexing issue where their wired Ethernet connection unexpectedly caps at 100Mbps, despite previously experiencing higher speeds. If you’re facing a similar problem, it can be frustrating, especially with a new or recently built system. In this article, we’ll explore potential causes and provide a step-by-step guide to troubleshoot and resolve this issue, including when a motherboard replacement might be necessary.
Understanding the Context
Suppose you have a modern motherboard, such as the GIGABYTE B650M AORUS ELITE AX (WIFI+BT) AM5, and you notice your network speeds stubbornly max out at 100Mbps. Your download speeds, which previously ranged between 600-700Mbps, suddenly drop and remain stuck at the 100Mbps ceiling.
This scenario suggests that the problem could be related to the LAN port or network adapter, but comprehensive troubleshooting is essential to pinpoint the exact cause.
Initial Troubleshooting Steps
1. Verify the Cable and Modem Setup
- Test with a different Ethernet cable: Connect your modem directly to a laptop using a different cable. If the connection hits 600Mbps again, your cable and modem are functioning properly.
- Test the LAN port on your PC: Connect your laptop using the same cable to the LAN port behind your PC. Again, if speeds are normal, it indicates the cable and modem are not at fault.
2. Check System Network Settings
- Open the Control Panel > Network and Internet > Network and Sharing Center > Ethernet and verify the speed displayed — it should ideally be higher than 100Mbps.
- Check the ‘Aggregated Link Speed (Receive/Transmit)’ in device properties or system information; if it shows 100/100 Mbps, it confirms the limitation.
3. Modify Network Adapter Settings
- Access your network adapter properties and change the ‘Speed & Duplex’ setting from ‘Auto Negotiation’ to ‘1.0 Gbps Full Duplex’ or ‘2.5 Gbps Full Duplex’.
- Reset network settings through Windows Settings or Command Prompt commands like
netsh int ip reset. - Run system health checks (
sfc /scannow,chkdsk,DISM /Online /Cleanup-Image /RestoreHealth
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