How to perform a line test at the network box

If your internet speed test is slower than you expect, testing your own service can help you determine where the problem lies.

What is the network interface device?

The network box (sometimes called the "network interface device" or NID) connects the provider network to the wiring inside your home. It's where our outside wiring meets your inside wiring.

How to test service at the network box

First, locate your network box. They are usually about 6" by 9" and gray, attached to the outside of your home near your electric meter and other utility connections. If you don't see it outside, it could be in your basement or attic. Sometimes it is painted to match the exterior color.

Note: If you live in an apartment, ask your building manager for access; you may have a test jack inside your unit. If you live in a mobile home, the network box may be attached to a pole on your lot.


To test your internet or phone service, you will need to bring with you:

  • A flathead screwdriver 
  • Your modem and modem cables 
  • An extension cord (in many cases)


Then, follow the steps below.


1. Use a flathead screwdriver to open the "CUSTOMER ACCESS" portion of the telephone network box.

2. Locate the test jack that has a wire running from the house plugged into it. Unplug that cord from the test jack.

3. Plug one end of the modem cord (looks like a phone cord) into the test jack. Plug the other end into the port labeled "DSL / LINE" on the side or back of your modem.

4. Make sure the modem's power cord is firmly plugged into the small round port on the modem, then plug it into an outlet. You may need an extension cord to reach the nearest outlet, which could be outside, in the garage or in your house.

5. Wait for the DSL status light on the modem to turn solid green This may take up to 5 minutes. Connect a device to the modem, ideally using an Ethernet cable for a direct connection, or use a wireless (WiFi) connect if needed. Then run another speed test. If you have any questions, chat with tech support to review your findings.

Important reminder: Once you've finished testing, be sure to plug the original cord back into the test jack (the reverse of step 1 above). Then close the box cover and secure the screw tightly.

Now, let's look at your results

QUESTION: Did you experience the same problem at the network box that you were having previously?

If YES, then most likely there is an issue with outside equipment or phone/internet lines belonging to the CenturyLink network. Submit a repair request so that CenturyLink can fix the problem.

If NO, then this means there is likely an issue with your inside wiring, jacks or equipment configuration. Try these common troubleshooting tips for slow internet. Or check your WiFi, as in some cases it's the wireless connection that is causing things to be sluggish, rather than the wired internet connection.


You can also run the Troubleshooter, which can identify and diagnose common problems. If not, you can also create a service request from there.

Need assistance? Contact technical support by phone or chat. We're here to help!

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