Slow Ethernet Speed: How to Fix Wired Connection Speed

Step 1: Check link speed in your OS

On Windows: open Device Manager > Network Adapters > right-click your NIC > Status. The Speed field should read 1.0 Gbps. If it shows 100 Mbps, the connection has negotiated down — either the cable, port, or NIC is limiting the link. On macOS: hold Option and click the Wi-Fi menu bar icon, or go to System Information > Network > Ethernet to see link speed.

Step 2: Test a different Ethernet cable

A damaged cable or a cable that is only Cat5 (not Cat5e or higher) will negotiate at 100 Mbps instead of 1000 Mbps. Cat5e, Cat6, and Cat6a all support gigabit. Check the printing on the cable jacket — it will say Cat5, Cat5e, Cat6, etc. Replace with a known-good Cat5e or Cat6 cable and check if the link speed changes to 1.0 Gbps.

Step 3: Try a different port on the switch or router

A failing switch or router port can negotiate at 100 Mbps or drop packets even when the link shows 1 Gbps. Unplug the Ethernet cable from the current port and try a different port on the same switch or router. If speed improves, the original port is faulty.

Step 4: Update NIC drivers

Intel i219 and i225 NICs (found in most modern desktops and laptops) have known driver issues that cause speed negotiation problems and throughput drops. Download the latest driver directly from Intel's website rather than relying on Windows Update. On macOS, NIC drivers are part of the OS — update macOS to get fixes.

Step 5: Disable Energy Efficient Ethernet (EEE)

Energy Efficient Ethernet (EEE, also called Green Ethernet) reduces power consumption by lowering link speed during idle periods. On some NIC and switch combinations, EEE causes link instability and incorrect speed negotiation. Disable it in Windows: Device Manager > Network Adapters > right-click NIC > Properties > Advanced tab > find "Energy Efficient Ethernet" or "Green Ethernet" > set to Disabled.

Step 6: Test with a different switch

A failing switch — especially an unmanaged consumer switch that is several years old — can throttle throughput on specific ports or globally. If you have a secondary switch or can temporarily connect directly to the router, test speed without the switch in the path. Consistent improvement without the switch means the switch is the problem.

Frequently Asked Questions

Why is my ethernet showing 100 Mbps instead of 1000 Mbps?

A 100 Mbps link speed means the connection negotiated down from gigabit. The most common causes are: a Cat5 cable (not Cat5e) which only supports 100 Mbps, a damaged cable with broken wire pairs, a faulty switch or router port, or a NIC driver issue. Check the cable category printed on the jacket, try a different cable, and try a different port. If those don't help, update your NIC drivers and disable Energy Efficient Ethernet.

Can a bad cable slow ethernet speed?

Yes. A damaged Ethernet cable can cause two problems: link speed negotiation to 100 Mbps (if wire pairs are broken or the cable is only Cat5), and packet errors that cause retransmissions which reduce effective throughput even at gigabit link speed. A cable with internal damage may still link at 1 Gbps but show high error rates — use a cable tester or simply try a replacement cable.

What cable do I need for gigabit ethernet?

You need at minimum Cat5e for gigabit Ethernet (1000BASE-T). Cat5 (without the "e") only supports 100 Mbps reliably. Cat6 and Cat6a also support gigabit and offer better interference rejection for longer runs. For runs over 100 meters, Cat6a is recommended. For home use under 30 meters, Cat5e and Cat6 perform identically.