--- title: "Quantum Fiber / CenturyLink slow internet in United States: tests, evidence and complaints · Kilobat Guides" url: "https://kilobat.app/guides/quantum-fiber-slow-internet-complaint" description: "Quantum Fiber / CenturyLink internet slow or dropping out in United States? Check equipment, compare tests, keep evidence and follow the complaint route." --- # Quantum Fiber / CenturyLink slow internet in United States: tests, evidence and complaints If your Quantum Fiber / CenturyLink connection is slow or unreliable, start with these equipment checks. Then document a repeatable result and ask for a specific investigation. Applies to: C4000, C3000, C2100, C844 and C424 modems (menus as of 2026); the C3510 menu differs slightly. Customers with a SmartNID and 360 WiFi pods manage Wi-Fi only in the Quantum Fiber app. · Checked: 3 November 2026 ## When this helps - You use Quantum Fiber / CenturyLink in United States. - Your connection is slower than expected, drops out or performs badly at certain times. ## Check your Quantum Fiber and CenturyLink modem These checks apply to Quantum Fiber and CenturyLink modem. Check the model before following its menus. 1. Sign in and select **Modem Status › Connection Status** for the firmware, connection and IPv4 address. 2. Check **Internet Status** for authentication failures and session time. 3. Select **Utilities › System Log** for a timed list of system actions, or **Firewall Log** where offered. 4. Run **Utilities › Diagnostic Test** to check the WAN, PPP and DNS. ## Separate the service from your home Wi-Fi For the exact settings and supported equipment, see [the Quantum Fiber and CenturyLink modem guide](https://kilobat.app/routers/quantum-fiber). Do not factory-reset the equipment as a first step. A reset can erase service settings and interrupt phone service. 1. Compare a wired connection to the router with Wi-Fi on the same device. 2. Repeat the same test server during the slowdown and at a quieter time. 3. Record download, upload, latency and whether another household device was using the connection. ## How to complain to Quantum Fiber / CenturyLink Use [Quantum Fiber / CenturyLink’s official support](https://www.centurylink.com/home/help/internet/modems-and-routers/modem-status.html) to report the fault. Request a formal complaint reference if it remains unresolved. Include the plan wording, dates, test conditions, previous references and the specific outcome you want. Ask for a written response. For the local escalation route and conditions, follow [the United States complaint guide](https://kilobat.app/guides/us-internet-speed-fcc-complaint). ## Collect the evidence with Kilobat On a Mac, Kilobat can record connection checks and produce a support report. Review the report and add your test conditions before sharing. The basic report export is free. [Kilobat Pro’s complaint wizard](https://kilobat.app/internet-complaint) helps assemble your evidence, impact and requested resolution into a draft you review and send. Measurements cover this Mac while monitoring ran. They cannot prove whole-home uptime, establish provider fault or replace a required official measurement procedure. ## Sources - [Quantum Fiber Support: Modem settings in the GUI](https://www.quantumfiber.com/support/equipment/user-guides/gui-settings.html) - [Quantum Fiber Support: C4000XG modem user guide](https://www.quantumfiber.com/support/equipment/user-guides/c4000xg-modem.html) - [Quantum Fiber Support: How to restart your SmartNID or modem](https://www.quantumfiber.com/support/equipment/troubleshooting/restart-your-modem.html) - [Quantum Fiber Support: How (and when) to reset your modem](https://www.quantumfiber.com/support/equipment/troubleshooting/modem-reset.html) - [Quantum Fiber Support: How to install a 360 WiFi pod](https://www.quantumfiber.com/support/services/360-wifi/add-wifi-pod.html) - [Quantum Fiber Support: 360 WiFi FAQs](https://www.quantumfiber.com/support/services/360-wifi/faqs.html) - [CenturyLink Help: Security settings (port forwarding, UPnP, NAT)](https://www.centurylink.com/home/help/internet/modems-and-routers/advanced-setup/security-settings.html) - [CenturyLink Help: Configure QoS on your modem](https://www.centurylink.com/home/help/internet/modems-and-routers/advanced-setup/qos.html) - [CenturyLink Help: Wireless setup](https://www.centurylink.com/home/help/internet/modems-and-routers/wireless-setup.html) - [CenturyLink Help: Utilities menu](https://www.centurylink.com/home/help/internet/modems-and-routers/utilities.html) - [CenturyLink Help: How to check your modem firmware version](https://www.centurylink.com/home/help/internet/modems-and-routers/utilities/update-modem-firmware.html) - [CenturyLink Help: Modem status menu](https://www.centurylink.com/home/help/internet/modems-and-routers/modem-status.html) - [CenturyLink Help: WAN settings](https://www.centurylink.com/home/help/internet/modems-and-routers/advanced-setup/wan-settings.html) - [CenturyLink Help: Advanced setup in the modem settings](https://www.centurylink.com/home/help/internet/modems-and-routers/advanced-setup.html) Checked on 3 November 2026. ## Related guides - [Internet slower than advertised? Test it before you complain](https://kilobat.app/guides/internet-slower-than-advertised): A low speed test is a starting point. - [Wi-Fi slow but Ethernet fast? Find the wireless bottleneck](https://kilobat.app/guides/wifi-slow-ethernet-fast): If the same device is consistently faster on Ethernet, investigate the wireless path first. - [Slow internet complaint letter: a template with the evidence to attach](https://kilobat.app/guides/broadband-complaint-letter): A useful complaint says what happened, how you tested it and what you want the provider to do next.