How to test CenturyLink service at the NID (network phone box)

To find out if an internet or home phone connection problem is inside your home or outside in the CenturyLink network, you can check for an active signal at the "network interface device" (NID). 

What's a network interface device?

The NID is the point where our outside wiring (the provider network) connects to your inside wiring (the subscriber network). Some customers call it the telephone box or network box, while technicians usually call it "the NID."


This device is about 6 by 9 inches and gray (or painted to match the house). It's most often on the outside of the home near the electric meter. Sometimes it's in the basement or attic. It's usually labeled "Network Interface Device" or "Telephone Network Interface" on the outside.

Photo of network interface device, or NID, attached to exterior of house

Network interface device (NID) with "Customer Access" on the side

If you live in multi-unit housing, ask your building manager for help. You may have a test jack inside your unit. DO NOT try to open a network box that serves multiple tenants.
If you have fiber internet service, you have a different kind of terminal. If the box does NOT have a "Customer Access" label on it, STOP. It is likely a fiber network box, which cannot be opened by customers.
Photo of multi-tenant building network terminal - do not open

Provider access for multi-tenant housing

Photo of fiber network terminal - do not try to open

Provider access for fiber internet (ONT)

How to test service at the NID

To test your internet or phone service, you will need to bring these things with you to your NID:
  • Flathead screwdriver 
  • If testing internet service, modem and modem cables
  • If testing phone service, standard landline telephone
  • Extension cord (in many cases)


Then follow the steps below:


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

Illustration showing how to open network interface device with screwdriver

2. Locate the test jack that has a short wire plugged into it. Unplug that wire from the test jack. In some cases, there are two test jacks; you can pick either one to unplug and run your test.

Illustration showing test jack and wire inside network interface device

Select your service type to see the remaining instructions.

3. Plug the modem's DSL cord into the test jack and make sure the other end is plugged into the DSL or LINE port on the back of the modem.

Illustration showing DSL line plugged into test jack on network interface device

4. Plug the modem's power cord into an outlet, using an extension cord if needed. Make sure the other end of the power cord is plugged firmly into the round power port on the back of the modem. 

Illustration showing modem plugged into NID and into power outlet for testing

5. Wait while your modem boots up, which may take a few minutes. Watch for the DSL light to turn solid green. 

Simple illustration of modem showing power light, DSL light and Internet light all on and green

Test results: What color is the DSL light?

GREEN DSL LIGHT: The problem is most likely with the outside equipment or internet lines belonging to the CenturyLink network. Submit a repair request so that CenturyLink can fix the problem.

RED DSL LIGHT (OR OFF): The issue is most likely with your inside wiring, jacks, equipment, or modem settings. Try these common troubleshooting tips for slow internet. Or check your WiFi, as in many cases the wired internet connection is fine, and it's the WiFi signal that is sluggish.

You can also run Troubleshooter, which can diagnose common problems. 

3. Plug the telephone cord into the test jack and make sure the other end is plugged firmly into the phone. Plug the phone's power cord into an outlet or extension cord.

4. Listen for a dial tone in the receiver.

Test results: Do you hear a clear dial tone?

THERE IS NO DIAL TONE or the tone is faint or intermittent: The problem is most likely outside, with our wiring or equipment. Submit a repair request and we will send out a technician. You will not be charged for the visit if the problem is confirmed to be on the CenturyLink side.

THERE IS A CLEAR DIAL TONE at the network box: The problem is most likely inside, with your own wiring or equipment. Use Troubleshooter to get more help walking through steps to check and fix equipment.

Important! Once you're done testing, be sure to plug the original wire back into the test jack (the reverse of step 1). Then close the box cover and tighten the screw securely.

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

Troubleshoot problems with your service

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