Troubleshooting Your Fiber Internet Connection: How to Boost Your Download Speed and Avoid Captchas


What could be causing my internet speed to drop drastically and inconsistently, despite having a fiber connection and no VPN?

I have a CenturyLink fiber internet service that was working fine until recently, when my download speed went from around 950mbps to as low as 4mbps, while my upload speed remained high. The speed fluctuates randomly and is worse on wifi than on ethernet. I have contacted CenturyLink and they have replaced the modem, the ONT, and the cables, but nothing has changed. They keep asking me if I am using a VPN, which I am not. I also get captcha requests from Google when I search for something, indicating some suspicious activity on my network. I am using Mac computers and I don’t know much about VPNs or how to check if someone is siphoning my internet. How can I troubleshoot this issue and find out what is going on?


If you are experiencing a sudden and significant drop in your internet speed, there could be several possible causes. Some of them are related to your internet service provider (ISP), some are related to your network devices, and some are related to your computer settings or applications. In this article, we will explore some of the most common scenarios and how to troubleshoot them.

Scenario 1: Your ISP is having issues

One of the first things to check is whether your ISP is having any problems with their service or infrastructure. Sometimes, ISPs may experience outages, congestion, maintenance, or other issues that affect their performance and reliability. To find out if this is the case, you can try the following steps:

  • Contact your ISP and ask them if they are aware of any issues or disruptions in your area. They may be able to provide you with more information or an estimated time of resolution.
  • Visit your ISP’s website or social media accounts and look for any announcements or updates regarding their service status. You may also find other customers reporting similar issues or complaints.
  • Use a third-party website or app that monitors the internet speed and availability of different ISPs around the world. For example, you can use [DownDetector](, [Speedtest](, or [Fast]( to see if your ISP is experiencing any slowdowns or outages.
  • If your ISP is having issues, there is not much you can do except wait for them to fix them. However, you can try to switch to a different DNS server, which may improve your browsing speed and security. DNS stands for Domain Name System, and it is responsible for translating website names into IP addresses. Sometimes, your ISP’s default DNS server may be slow, overloaded, or blocked by some websites. To change your DNS server, you can follow these steps:

  • On your Mac, go to System Preferences > Network > Advanced > DNS.
  • Click the + button and enter the IP address of a different DNS server. You can use a public DNS server, such as Google DNS ( and or Cloudflare DNS ( and
  • Click OK and then Apply to save the changes.
  • Scenario 2: Your network devices are malfunctioning

    Another possible cause of your internet speed drop is that your network devices, such as your modem, router, or cables, are malfunctioning or outdated. These devices are essential for connecting your computer to the internet, and if they are not working properly, they can affect your speed and stability. To troubleshoot this scenario, you can try the following steps:

  • Restart your modem and router. This is a simple but effective way to resolve many network issues, as it clears the cache and resets the settings. To do this, unplug the power cords from both devices, wait for about 30 seconds, and then plug them back in. Wait for a few minutes until the devices are fully rebooted and the lights are stable.
  • Check your cables and connections. Make sure that your cables are not damaged, loose, or tangled, and that they are plugged into the correct ports. If possible, use a different cable or port to see if that makes a difference. If you are using a wireless connection, make sure that your router is placed in a central and open location, away from any sources of interference, such as walls, metal objects, or other electronic devices. You can also try to change the wireless channel or frequency of your router, which may reduce the interference from other nearby networks. To do this, you need to access your router’s web interface, which usually requires entering its IP address into your browser. You can find the IP address and the login credentials on the back or bottom of your router, or in the user manual. Once you are logged in, look for the wireless settings and change the channel or frequency to a less crowded one.
  • Update your firmware and drivers. Firmware is the software that runs on your network devices, and drivers are the software that allows your computer to communicate with them. Sometimes, these software may have bugs, vulnerabilities, or compatibility issues that affect your network performance. To update your firmware, you need to access your router’s web interface, as explained above, and look for the firmware update option. Follow the instructions on the screen to download and install the latest version of the firmware. To update your drivers, you need to go to System Preferences > Software Update on your Mac, and check for any available updates. Alternatively, you can visit the manufacturer’s website and download the latest drivers for your network devices.
  • Scenario 3: Your computer settings or applications are interfering

    The last possible cause of your internet speed drop is that your computer settings or applications are interfering with your network connection. Sometimes, your computer may have some settings or features that limit or prioritize your bandwidth usage, or some applications may be consuming a large amount of your bandwidth in the background. To troubleshoot this scenario, you can try the following steps:

  • Disable any VPNs or proxies. VPNs and proxies are services that allow you to access the internet through a different location or server, which may improve your privacy or bypass some restrictions. However, they can also slow down your internet speed, as they add an extra layer of encryption and routing to your connection. If you are not using a VPN or proxy, you can disable them by going to System Preferences > Network > Advanced > Proxies and unchecking any boxes that are checked. If you are using a VPN or proxy app, you can quit or uninstall it from your Mac.
  • Check your bandwidth usage. Bandwidth is the amount of data that you can send or receive over your network connection in a given time. If you are using too much bandwidth, your internet speed may suffer. To check your bandwidth usage, you can use a third-party app, such as [Bandwidth+]( or [iStat Menus](, which can show you how much bandwidth each app or process is using on your Mac. You can also use the built-in Activity Monitor app, which you can find in the Applications > Utilities folder. Once you open the app, click on the Network tab and sort the processes by the Sent Bytes or Received Bytes columns. You can then identify and close any apps or processes that are using a lot of bandwidth, such as streaming, downloading, or syncing services.
  • Reset your network settings. If none of the above steps work, you can try to reset your network settings, which may resolve any configuration or compatibility issues that are affecting your network connection. To do this, you need to delete some files from your Mac, which may require administrator privileges. Follow these steps:
  • Quit any apps that are using the internet.
  • Go to Finder > Go > Go to Folder and enter `/Library/Preferences/SystemConfiguration/` in the box. Click Go.
  • Select the following files and move them to the Trash:
  • NetworkInterfaces.plist
  • preferences.plist
  • Restart your Mac and reconnect to your network.
  • Conclusion


this article, we have discussed some of the possible causes of your internet speed drop and how to troubleshoot them. We have covered three scenarios: your ISP is having issues, your network devices are malfunctioning, and your computer settings or applications are interfering. We have also provided some steps and tips to resolve each scenario. We hope that this article has helped you to improve your internet speed and enjoy a better online experience.

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