Router to Modem/PC Auto-Negotiation at 100Mbps (not 1Gbps)

Published by Nyau Wai Hoe - Updated on

In the age of fiber optics and high-speed broadband, an internet speed of 1Gbps is becoming the new norm. However, sometimes you might find that the connection between your router and modem, or your router and PC, auto-negotiation at a speed of just 100Mbps instead of the expected 1Gbps. This speed reduction can lead to a noticeable decline in your overall internet experience, making downloads, streams, and other online activities significantly slower. While it might seem like a perplexing issue, there are a few common culprits that can be at the root of this problem. In this article, we’ll walk you through the steps to diagnose and fix the issue, ensuring that your devices communicate at their maximum potential speed.

Also see: Change Ethernet from 100Mbps to 1Gbps in Windows 11/10

Router to Modem or PC Auto-Negotiate at 100Mbps but not 1Gbps

Resolving 100Mbps auto-negotiation cap instead of 1Gbps between router and modem/PC

1. Check and re-seat the Ethernet cable

One of the most common reasons for a reduced speed between devices is a loose or improperly seated Ethernet cable. Sometimes, the physical connection between the router and the device might not be as snug as it should be, leading to a poor signal and thus a reduced speed.

  1. Turn off both your router and the connected device (modem or PC).
  2. Unplug the Ethernet cable from both ends.
  3. Take a moment to inspect the Ethernet ports on both devices. Ensure there’s no dust, debris, or any visible damage.
  4. Gently plug the Ethernet cable back into both ports. Ensure you hear a ‘click’ which indicates the cable is securely locked in place.
  5. Turn on both devices and check the connection speed.
  6. Try to do this a couple of times (plugging out and plugging back in) and see if it will auto negotiate correctly each time. This is a common but sometimes effective workaround.

Replugging LAN cable on Router Modem

After re-seating the cable, check your connection speed. If it’s still not reflecting the 1Gbps you’re expecting, it’s time to move to the next potential solution.

Linked issue: Ethernet Internet Speed Capped at 100 Mbps (Fix)

2. Try a different Ethernet cable

Faulty or substandard Ethernet cables are a frequent cause of network issues. Not all cables are built the same, and over time, even the best can degrade or become damaged. This can result in incorrect auto-negotiation speeds (100Mbps or slower) between the router, modem, and PC.

Types of Ethernet cables:

  • Cat 5: Supports speeds up to 100Mbps
  • Cat 5e: Supports speeds up to 1Gbps
  • Cat 6: Supports speeds up to 10Gbps (for distances up to 55 meters)
  • Cat 6a & above: Supports higher speeds and longer distances

Auto-Negotiation Cap at 100Mbps

If you’re using an older cable, especially one that is Cat 5 or below, it might be the reason why you’re not getting speeds above 100Mbps.

  1. Disconnect your current Ethernet cable.
  2. Connect a different, preferably newer, Ethernet cable between your router and the other device.
  3. Check the connection speed. If the speed is now 1Gbps or closer to it, then the previous cable was likely the issue.

Remember, a cable might look perfectly fine on the outside but can still have internal issues affecting its performance. Switching to a different cable eliminates this variable. However, if the problem persists, there might be other underlying causes.

Related problem: Windows 11 Ethernet “Unidentified Network” (How to Fix)

3. Router configuration issues (auto-negotiation settings)

Even if your hardware is in perfect shape, incorrect settings within your router’s configuration can be a barrier to achieving gigabit speeds. The router’s settings play a pivotal role in determining how data is transmitted through your network.

  1. Access your router’s administration page. This is typically done by entering the router’s IP address into a web browser. Common addresses include or, but refer to your router’s manual if unsure.
  2. Once logged in, navigate to the “Network” or “LAN/WAN” settings section.
  3. Look for options such as “Link Speed”, “Auto-Negotiation”, or “Connection Speed”. Ensure that these are set to the highest available speed, usually indicated as “1000Mbps” or “1Gbps”. If it’s set to “Auto”, the router should automatically choose the fastest speed, but sometimes manual selection is more reliable.How to set Router Auto-Negotiation setting to 1Gbps instead of 100Mbps
  4. Save any changes made and then restart your router to ensure the new settings are applied.

While inside your router settings, it’s also a good opportunity to check for firmware updates. Manufacturers often release updates to improve performance, fix bugs, or enhance security.

Related resource: Ethernet Not Working in Windows 11 (Fix)

4. Check network card properties

Your computer’s network card, often known as the Ethernet or LAN adapter, has its own settings that can influence connection speeds. Incorrectly configured settings (particularly the Auto-Negotiation setting) can prevent the card from communicating at the highest possible speed.


  1. Access the Network Connections Panel: Right-click on the “Start” button, select “Network Connections” or “Network and Sharing Center”, and then choose “Change adapter settings” on the sidebar.
  2. Right-click on your active Ethernet connection and select “Properties”.
  3. Click on the “Configure” button or something similar, depending on your operating system.
  4. Navigate to the “Advanced” tab.
  5. In the property list, find “Speed & Duplex” or a similar naming convention.
  6. The default setting is usually “Auto-Negotiation”. However, if it’s set to anything lower than the expected speed, like “100Mbps Full Duplex”, that’s likely the culprit. Change the value to “1.0 Gbps Full Duplex” or the highest available setting.Windows 11 Set Auto-Negotiation to 1Gbps
  7. Click “OK” to save the changes, then restart your computer to ensure the new settings take effect.

By ensuring that both the router and your computer’s network card are configured to auto-negotiate at gigabit speeds, you remove two potential bottlenecks from your network setup.

Other concern: File Transfer Speed Very Slow or Drops to Zero in Windows 11

5. Hardware limitations

Sometimes, the bottleneck might not be due to settings or faulty cables but inherent hardware limitations. Not all devices are built to support gigabit speeds, especially older models. If even a single device supports only 100Mbps and doesn’t accommodate gigabit speeds, the entire chain of connection will auto-negotiate to 100Mbps.

Steps to check and understand hardware limitations:

  1. Router/Modem Specifications: Consult your router or modem’s user manual or look up its specifications online. Determine the maximum supported speed for LAN/WAN ports. If they are rated at 100Mbps, they won’t be able to handle 1Gbps, regardless of other factors.Auto-Negotiation 100Mbps Gigabit Router
  2. Computer’s Network Card: The age and type of your computer can impact the speeds you achieve. To check:
    • For Windows: Open “Device Manager”, expand the “Network adapters” section, and locate your Ethernet adapter. Look up its model online to determine its maximum supported speeds.
    • For macOS: Go to “Apple Menu” > “About This Mac” > “System Report”, and under “Hardware” select “Ethernet Cards”. Check the model and look up its specifications online.
  3. Upgrade Hardware if Necessary: If your hardware inherently supports only 100Mbps, consider upgrading to a more recent model. Modern routers, modems, and network cards are designed to handle gigabit speeds.

Remember, even if you have a gigabit connection from your ISP, the actual speeds you experience on devices are only as fast as the weakest link in your hardware chain.

Windows 11 Auto-negotiation 1Gbps vs 100Mbps

6. ISP Limitations

While we often focus on our internal network setup, sometimes the limitation might come from outside, specifically from your Internet Service Provider (ISP). ISPs offer various packages, each with its own speed cap, and sometimes the promised speeds might not match the actual provision.

  1. Review your plan: Double-check the speed tier you’ve subscribed to with your ISP. If your plan offers up to 100Mbps, that will be the maximum speed achievable regardless of your internal setup.ISP Internet Plan
  2. Run a speed test: Use online tools like or to gauge your current internet speeds. Ideally, perform this test with a device connected directly to the modem via Ethernet to get the most accurate reading.Internet Connection Speed Test
  3. Contact your ISP: If you’re subscribed to a gigabit plan but not getting the expected speeds, reach out to your ISP. They can provide insights, perform remote tests, and sometimes even boost the connection from their end.
  4. Equipment provided by the ISP: Sometimes, the modem or gateway device provided by the ISP might not be optimized for the highest speed tiers. Inquire if they have newer or different models available that might be better suited for gigabit connections.

It’s always a good practice to have open communication with your ISP. They can provide insights, updates, or solutions you might not be aware of.

7. Factory reset the router (not recommended)

If none of the aforementioned solutions work, as a last resort, you might consider performing a factory reset on your router. This action will revert the router to its original settings, potentially clearing any auto-negotiation configuration issues. However, this approach comes with significant considerations and risks.

Steps and considerations for Router’s factory resetting:

  1. Backup configuration: Before you proceed with the reset, ensure you backup your current router configuration. Most routers offer a “Backup” or “Save Config” option within their admin interface. This allows you to save your settings and restore them after the reset, if necessary.
  2. Potential data loss: Understand that a factory reset will erase all your personalized settings. This includes Wi-Fi network names (SSIDs), passwords, port forwarding rules, and any other custom configurations.
  3. ISP credentials: Some ISPs require specific login credentials to access the internet. Ensure you have these details at hand, as a factory reset might erase them, and you’ll need to re-enter them to re-establish your internet connection.
  4. Initiate the reset: Usually, routers have a small “Reset” button which, when pressed and held for about 10 seconds, will start the reset process. Alternatively, the router’s admin interface might have a “Factory Reset” or “Restore Default Settings” option.Factory reset router
  5. Reconfigure your router: After the reset, you’ll need to reconfigure your router. This includes setting up Wi-Fi networks, entering ISP credentials, and applying any other custom settings.
  6. Reconnect devices: Devices that were previously connected to your Wi-Fi might require reconnection or re-authentication due to the changed settings.

Always treat a factory reset as a last-resort measure due to its sweeping implications. If you’re unsure about any step, it might be worth consulting with a tech-savvy friend or professional.


In many situations, if your network speed suddenly drops, settling at an auto-negotiation cap of 100Mbps, after having worked flawlessly for a long time, the culprit is often a faulty or damaged Ethernet cable. While re-seating the cable on both ends (router, modem, or PC) can temporarily remedy the situation, it’s a sign that your cable is on its way out. If this quick fix does the trick, consider it a clear signal to order a replacement cable soon.

On the other hand, if these issues arise immediately after setting up a new network connection, the root of the problem might be more complex. In such cases, it’s essential to explore the range of potential causes and solutions outlined above, as network hitches can span from simple hardware mishaps to intricate configuration challenges.

    Nyau Wai Hoe
    Nyau Wai Hoe is the Founder and Chief Editor of With a degree in software engineering and over 12 years of experience in the tech support industry, Nyau has established himself as an expert in the field, with a primary focus on the Microsoft Windows operating system. As a tech enthusiast, he loves exploring new technologies and leveraging them to solve real-life problems.

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