CenturyLink Speed Test

This diagnostic tool validates the performance of your CenturyLink internet connection. It is important to note that CenturyLink operates two very different networks: High-Speed Internet (DSL), which uses traditional copper phone lines, and Quantum Fiber, which uses dedicated fiber optic cables. Your test results will vary significantly depending on which technology powers your home.

While Quantum Fiber is highly stable, legacy DSL connections often experience speed degradation due to distance from the local node or interference from internal phone wiring.

Understanding Your Speed Metrics

When analyzing your results, look for these three key indicators:

Download Speed: On DSL plans (e.g., 20, 40, or 100 Mbps), speeds can fluctuate during peak hours or bad weather. On Quantum Fiber plans (e.g., 940 Mbps), speeds should remain consistent and near-gigabit levels.

Upload Speed: This is the main differentiator. DSL plans typically have very low upload speeds (often less than 10% of download speed), which causes lag in video calls. Fiber plans offer Symmetrical Speeds (Upload equals Download).

Latency (Ping): DSL connections often have higher latency (40-60ms) due to the copper infrastructure. Fiber connections should typically show ping times under 10ms.

What Results Should You Expect?

The "Distance" Factor (DSL Only)

If you are on a DSL connection, your speed is physically limited by the length of the copper wire from your home to the neighborhood box (DSLAM). Typical benchmarks include:

Download Speed: ~80-90% of the "up to" speed listed on your bill.

Upload Speed: Often capped at 5 Mbps or lower on copper lines.

Stability: Older lines may drop connection during rain or if the phone line has static.

If you pay for "Up to 40 Mbps" but consistently get 20 Mbps, you may be too far from the hub to physically receive the faster signal. This is a limitation of physics, not a router fault.

Why Is Your CenturyLink Connection Slow?

Before contacting support, check these common configuration faults:

Missing DSL Filters: If you have a landline phone, you must have a microfilter installed on every phone jack. Without these filters, phone calls will disconnect your internet or severely slow it down.

Old Wiring: Internal phone wiring in older homes often degrades DSL signals. Connecting the modem directly to the NID (Network Interface Device) box outside can verify if the issue is inside your walls.

C4000 Modem Issues: Users with the Greenwave C4000 series modems often report firmware bugs requiring a reboot to restore speeds.

CenturyLink Technical Details

How to Get an Accurate Test

Wi-Fi interference makes it difficult to diagnose line issues, especially on DSL connections where bandwidth is already limited.

To confirm the actual speed reaching your modem, connect a Cat5e or Cat6 Ethernet cable directly from the modem's yellow LAN port to a laptop. If this wired test shows speeds matching your bill, your DSL line is healthy, and the slowness is caused by Wi-Fi congestion.

When to Call Support

Escalate the issue to CenturyLink if you observe these specific failures:

Blinking Red DSL Light: If the "DSL" or "WAN" light is flashing red, the line is physically disconnected.

Static on Phone: If you hear crackling on your landline, the copper wire is damaged, which will kill your internet speed.

Walled Garden: If you are redirected to a CenturyLink activation page instead of the internet.

You can troubleshoot via the CenturyLink App or by calling 800-244-1111.