Troubleshoot your fiber connection

Before troubleshooting your CenturyLink Fiber connection, it may be helpful to know something about how we install the service.

A small box, called an optical network terminal (ONT) will be installed outside or inside your home. 

Home Networking

This connects to your home power and to your CenturyLink fiber-compatible router (also called a “residential gateway”). The router can then connect to your computers and other devices by WiFi or with an Ethernet cable.

How to check your router

From the fiber terminal, an Ethernet cable will run either directly into your router, or first to a wall jack and then to your router (depending on whether the terminal is installed outside or inside).

The Ethernet cable plugs into to the WAN/LAN port on the back of the router. Once this is connected, you will see a solid green light next to the WAN/LAN indicator on the front.

No "WAN/LAN" light?

The Wide Area Network (WAN) light shows that your router is connected to the fiber terminal. If this light is off, it means you aren’t connected to the network. The most common causes of this are loss of power to the terminal (ONT) or an unplugged network cable.

Start by checking the connections on the back of the modem. 

  • Make sure you have an Ethernet cable plugged into the WAN port on the back (see below). If you have a third-party modem, sometimes this is labeled the INTERNET port.
  • Make sure the power cord is plugged firmly into the small round port (not pictured)

WAN Lights

Once you've made sure everything is correctly plugged into the router, next make sure the other end of the Ethernet cable is securely plugged into either the wall jack or the indoor terminal box.

Now check the WAN/LAN light again.

Still not on? Check to see whether any electrical breakers or outlets with circuit breakers in them have been tripped. 

If your fiber terminal was installed in your garage or outside your home, it's likely that it plugs into a ground-fault circuit interrupter (GFCI) outlet. These have built-in circuit breakers that can trip when there is an overload or other issue with the electrical current. They are commonly used in homes for safety.

No "INTERNET" light?

If you have a solid WAN light but no internet light (or if the internet light is flashing red and green), this is an issue for the CenturyLink repair team. Please contact us to get help. 

Fiber internet equipment

A fiber internet connection involves the use of some specialized equipment. Learn more below about the optical network terminal (ONT), the wall wart device, and battery back-up units often used with fiber internet service.

Optical Network Terminal (ONT)

Your fiber internet connection, which runs from the main network to your property over fiber-optic cable, does not provide its own power, and can’t be hooked up directly to your personal equipment.

Therefore, a special box, called an optical network terminal (ONT), has to be installed inside or outside your home. This terminal transmits the fiber output from the main line to your router (gateway), which can then connect to your phone and internet devices.

Since the terminal is powered by your home electrical supply, it will typically be plugged into a GFCI electrical outlet. Some ONTs also have the option of battery backup, allowing them to maintain service in the event of a power outage.


In this photograph of a fiber terminal, you can see the ports where the wiring that connects the terminal to your home is plugged in.

ONT Lights

Where is the optical terminal (ONT) installed?

The terminal box can be installed in a few different locations around your home.

An outdoor ONT is typically located behind the home near other utility connections. Common indoor locations include the garage or a utility closet.

If you live in an apartment complex or condo, your optical terminal box may be accessible only with the help of a technician. Or some newer communities may have internal terminal boxes. If needed, you can contact your property manager to ask about getting access.

CenturyLink uses two different manufacturers for our ONTs: Adtran and Calix. The terminals will always be branded with the company logos you see below.

"Wall wart" power device

If your home does not have a circuit-breaker (GFCI) outlet available, our technician will install a "wall wart" on the power cord from the fiber terminal (ONT).


​This funny name is a common device that converts the AC power to 12-volt DC power. 

Power Wall Wart Device

There’s a RESET button on the wall wart, just like on a GFCI outlet. So if there’s a surge in electrical current, the circuit will trip and cut off power to the optical terminal, protecting it from being blown. In this case, you would just push the reset button to restore power to your terminal box.

Battery backup units

If you are a CenturyLink residential customer with Fiber Gigabit service (or any non-line-powered voice service), you can purchase a battery backup unit (BBU) from us. 

Battery Back-up - back

This little box, also known as an Uninterruptable Power Supply (UPS), will keep your service up and running during a power outage.
The unit provides temporary power to essential network equipment and devices, allowing you to dial 911 in an emergency. You can purchase either an 8-hour or a 24-hour backup unit. 

Battery Back-up - front

It’s important to note that the backup unit can't guarantee functionality in all outage events and will depend upon whether or not the network itself is in operation. While running on backup power, you may not be able to access the internet, again depending on the nature of the outage.

Whether you use a CenturyLink backup unit or one from a different supplier, you are responsible for monitoring, replacing and properly disposing of the batteries in the backup unit. You need to check the BBU at least twice a year to make sure it is functional and ready for use.

Warning Icon

Failure to maintain your battery back-up unit may cause loss of access to Emergency 911 and other services during a power outage.

More information regarding battery backup units is available from the supplier website. Search for these two battery models:  PP36PB-GRST-2-24D and PP36PB-12BBU-2-24D

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