How to Fix a USB-C to Ethernet Adapter Not Working: Driver Updates, Speed Negotiation Issues, and Mac/Windows Troubleshooting for 2.5G Adapters

You plug a USB-C to Ethernet adapter into your laptop, expect a fast wired connection, and get nothing — or a frustratingly slow 100 Mbps link instead of the 2.5 Gbps you paid for. This is one of the most common wired-networking headaches in 2026, affecting MacBooks, Windows laptops, and even Linux machines. If the adapter works but the connection itself is dead, our broader guide on how to fix Ethernet not working on Windows, Mac, and Linux covers the wider set of causes. The good news: nearly every failure has a clear, fixable cause. This guide walks through each one in order, from the simplest checks to chipset-specific driver fixes.

Step 1: Identify Your Adapter’s Chipset

The chipset inside your adapter determines which driver it needs and whether your OS supports it natively. The three chipsets you’re most likely to encounter in 2026:

• Realtek RTL8153 / RTL8153B: The most common 1 Gbps chipset. Windows 10/11 includes inbox drivers. macOS supports it natively as of macOS Monterey and later.
• Realtek RTL8156 / RTL8156B: The 2.5 Gbps version. Windows 10/11 does not include this driver by default — you must install it manually from Realtek. macOS Sonoma and Ventura support RTL8156B natively; older macOS versions require a manual driver.
• ASIX AX88179 / AX88179A: Common in older third-party adapters and some OEM hubs. Apple removed native ASIX support starting with macOS Big Sur (11.0), breaking many adapters that worked on Catalina. Windows 10/11 requires a signed driver from ASIX.

On Windows, open Device Manager → Network Adapters to see the listed device name and chipset. On macOS, go to System Information → USB to identify the connected device. Knowing your chipset before troubleshooting saves time.

Fix on Windows: Driver Issues and Speed Negotiation

Install or Update the Driver

Windows 11 includes a generic CDC-ECM driver that works with many 1 Gbps USB Ethernet adapters but does not handle 2.5 Gbps Realtek or ASIX adapters correctly. If Device Manager shows your adapter under Network Adapters with a yellow warning triangle, or the adapter shows as “USB 10/100/1000 LAN” when you expected 2.5G, the inbox driver is incorrect.

For RTL8156 / RTL8156B adapters: download the USB 2.5G Ethernet LINUX driver package from Realtek’s official site (not the PCIe 2.5G driver — they are different). Run the installer, reboot, then confirm the adapter shows as “Realtek USB GbE Family Controller” or “Realtek 2.5G USB Ethernet Controller” in Device Manager.

For ASIX adapters: download the signed Windows driver from the ASIX website directly. After installation, right-click the adapter in Device Manager, select Properties → Advanced, and verify the Speed & Duplex setting is set to “Auto Negotiation”.

Fix USB Power Management Killing the Adapter

Windows 11 aggressively suspends USB devices to save power. This can disconnect your Ethernet adapter intermittently or prevent it from being recognized after the system wakes from sleep. To disable this:

1. Open Device Manager → expand Universal Serial Bus Controllers.
2. Right-click each USB Root Hub entry → Properties → Power Management.
3. Uncheck “Allow the computer to turn off this device to save power.”
4. Repeat for every USB Root Hub listed.

Also disable USB Selective Suspend: open Power Options → Change plan settings → Change advanced power settings → USB Settings → USB Selective Suspend Setting → set to Disabled.

Force Re-Detection After Windows Update

Windows feature updates occasionally overwrite third-party Ethernet adapter drivers with the generic Microsoft version, breaking 2.5G adapters. If your adapter stopped working after a Windows update, uninstall the adapter in Device Manager (right-click → Uninstall device, check “Delete the driver software”), unplug the adapter, reboot, then re-run the manufacturer driver installer before plugging the adapter back in. This clears any driver conflict introduced by the update.

Fix on macOS: ASIX Adapters and Native Driver Gaps

ASIX Adapters on macOS Ventura and Sonoma

If your USB-C hub or adapter uses an ASIX AX88179 or AX88179A chipset and stopped working when you upgraded to macOS Big Sur or later, this is a known compatibility break. Apple removed the kernel extension (kext) that drove ASIX adapters natively. You have two options:

• Install the ASIX macOS driver: ASIX publishes a signed kext for macOS. Download it from the ASIX website, install it, then approve the system extension under System Settings → Privacy & Security → Security. Note that kext installation requires a reboot and SIP (System Integrity Protection) must remain enabled — the signed ASIX kext does not require disabling SIP.
• Replace the adapter: A Realtek RTL8156B-based adapter is natively supported on macOS Ventura and Sonoma with no driver installation. Adapters from Cable Matters, Plugable, and Anker using RTL8156B are widely available and eliminate the driver problem permanently.

Adapter Not Appearing in macOS Network Settings

Even with a working driver, macOS sometimes fails to add a new Ethernet interface to your active network service order. If System Information shows the adapter under USB but no Ethernet option appears in System Settings → Network, click the “+” button, select Interface → USB 10/100/1000 LAN (or equivalent), add it, and apply. If the interface appears but shows “Not Connected,” verify the Ethernet cable is seated firmly at both the adapter and the switch or router port.

Why Your 2.5G Adapter Is Only Running at 100 Mbps or 1 Gbps

Speed negotiation failures are the most common 2.5G adapter problem and are usually caused by one of three things:

• Wrong cable category: 2.5GBASE-T requires Cat 5e or better. Cat 5 (without the “e”) is rated to 100 MHz and will not reliably negotiate above 1 Gbps. Check your cable label. If you’re unsure, replace it with a Cat 6 or Cat 6A patch cable.
• Switch or router port only supports 1G: A 2.5G adapter connected to a 1G port will auto-negotiate down to 1 Gbps — which is correct behavior, not a failure. Verify that the port you’re connecting to supports 2.5GBASE-T. Most consumer routers added 2.5G ports in 2022–2024; older routers and unmanaged switches typically max out at 1G. Run a speed test to confirm your actual throughput.
• Wrong Realtek driver installed: Realtek publishes both PCIe 2.5G drivers (for motherboard NICs) and USB 2.5G drivers (for adapters). Installing the PCIe driver on a USB adapter results in the adapter falling back to 1G or not negotiating at all. Uninstall any existing Realtek driver and re-install specifically the USB 2.5G package. Our dedicated guide on how to fix 2.5G and 10G Ethernet not working covers multi-gig speed negotiation in more depth.

USB Hub Interference

Connecting a 2.5G USB-C Ethernet adapter through a powered or unpowered USB 3 hub can cause intermittent disconnects or speed drops. USB 3 hubs running multiple high-bandwidth devices simultaneously (external SSD plus webcam plus Ethernet, for example) can saturate the hub controller’s available bandwidth, causing the Ethernet adapter to throttle or drop. For best results, connect your Ethernet adapter directly to a USB-C port on the laptop, not through a hub. If you must use a hub, choose one with a dedicated Ethernet chipset (rather than a general-purpose multi-port hub) and ensure it is powered by its own AC adapter. Our guide on Ethernet vs. WiFi speed explains why a wired connection is still worth the trouble for bandwidth-intensive tasks.

Quick Reference Checklist

• Identify chipset: Realtek RTL8153/8156 or ASIX AX88179/AX88179A
• Install the correct manufacturer driver — not the Windows inbox or macOS generic driver
• Disable USB Selective Suspend and USB power management on Windows
• On macOS: install the ASIX signed kext or switch to a Realtek RTL8156B adapter
• Use Cat 5e or better cable; verify the switch port supports 2.5GBASE-T
• Connect directly to the laptop USB-C port, not through a hub
• After a Windows update, reinstall the manufacturer driver from scratch