Take a tour of your modem

There's a lot of technology built into that small box that gives you access to the web. This article will unlock the key points about all those ports, flickering lights, and sticker details found on the modem.

By the way, most CenturyLink modems will closely resemble the modems used in this article. However, keep in mind that your modem may vary slightly. Not to worry, we'll do our best to point out potential differences across modems.

Back of the Modem: Ports and Connections

(1) DSL or LINE

On newer CenturyLink modems the DSL or LINE port is color coded GREEN and it looks just like a phone jack. Older modem models may not be color coded.

Use the GREEN phone cord to connect the DSL port directly to the phone jack in your wall. This phone line carries both a voice and data signal into the modem. However, the modem has a built in filter and will split the signal between voice and data. Therefore, this phone line does not need a filter. In fact, putting a filter on this line would prevent the data signal from reaching the modem and consequently preventing a connection to the Internet.

Although a GREEN phone cord is typically provided with your modem kit, any standard phone cord will work just as well.


The port labeled PHONE is typically black and is the size of a standard phone jack. The PHONE port lets you run a phone line to a nearby telephone. There is no need to put a filter on the phone line between the modem and the telephone. Because the modem has an internal filter, the data signal will already be filtered out.

A common mistake is to run a phone cord between the PHONE port on the modem and the phone jack in your wall. Remember, the phone cord from the wall should go directly into the DSL or LINE port in the back of the modem.Older modems may not have a phone port at all. If your modem does not have a phone port, and you want to run a traditional phone from the same wall jack as modem, then you will need to use a dual inline filter.


The yellow Ethernet ports on the back of the modem allow you to connect directly to the modem's network using a basic Ethernet cable. If you received your modem from CenturyLink, then your kit probably contained a yellow Ethernet cable. Something to be aware of, the Ethernet cable may look like a phone cord, but if you look closer you'll see it's slightly bigger.

Newer CenturyLink modems typically have four Ethernet ports. Older modems may only have one Ethernet port and the port may be labeled DATA. 

If your modem has more than one yellow Ethernet port, you can safely use any one of the yellow ports. The additional ports allow you to connect additional computers or peripheral equipment, like say a printer.

The data transfer capabilities of this port depend on the modem model. Looking for modem specifications?

(4) USB

There are actually two types of USB ports that you may find on a CenturyLink modem.

  • Newer modems typically have a Type A USB (4 pin rectangular slot) port. Although this type of USB port is shown in the example above the port is currently non-functioning. It may be enabled in a future firmware release.
  • Older modems typically have a Type B USB (4 pin square) port. This type of USB port is not shown in the example above. It is intended to connect the modem directly to a device that does not have an Ethernet port. This type of connection is not ideal, but is a viable alternative for some older devices. If by chance you are using the Type B USB port to connect a device, it's suggested to not also use the modem's Ethernet port(s).


The small red circle on the back of the modem labeled RESET allows you to either reboot the modem or to restore the modem to all of its default settings. This includes the wireless settings. If you forget your customized wireless credentials, you can use the RESET button to restore the modem's default Network Name (SSID) and the Network KEY or PASSPHRASE.

The button is recessed so you need to use the tip of a pen or the end of a paperclip to press the button.

  • Pressing and holding for less than 10 seconds will only reboot the modem.
  • Pressing and holding for more than 10 seconds will reset the modem defaults.

After resetting the modem, the power light will turn amber and you will need to run through the modem activation process again just as if it was a brand new modem being installed.

Something to keep in mind when you use RESET, any devices previously connected will no longer be able to connect until you enter the most current KEY or PASSPHRASE into the device's wireless connection.


To work, the modem requires a source of electrical power. A power adapter typically is provided with the modem. After you connect the power adapter to the modem and an electrical outlet, give the modem a minute or two to boot up and you'll see the POWER indicator light up on the front of the modem.

Newer CenturyLink modems do not have a power switch. If your modem does not have a "power" switch, then it is automatically turned on when you plug it in. Older CenturyLink modems may still also have a power ON/OFF switch. In addition to plugging in the power, make sure the switch is turned to the ON position.

It is possible that over time, the power adapter can go bad. If you've confirmed that your wall outlet works and the power adapter is properly attached to the modem, but the POWER light on the front of the modem does not light up, then you may need a new power adapter. Make sure that if you replace the power adapter that it has the proper voltage and amperage for your specific modem. You can find this information in the small print labeled POWER RATING on the sticker under the modem.

Front of the Modem: Indicator Lights and Modem Model


If the light near the POWER label is not lit up at all, then the modem is not receiving power or is not turned ON (if your modem has a power switch). You should check the cord to make sure it's completely plugged in and that there is no obvious damage to the cord.

A solid green light indicates the modem has power and is ON.

A red light typically indicates the modem is in the process of rebooting. However, if after several minutes it continues to be red, then it is an indication of hardware failure.

An amber (yellowish-orange) glow typically indicates the modem is in the process of either booting up or going through a firmware upgrade. However, if after several minutes it continues to be red, then it is an indication of a software failure.

(2) DSL

DSL, or Digital Subscriber Line, is the technology that is used by CenturyLink to provide you with access to the Internet over your local telephone network. When your modem is first powered ON, it will call out over the phone line to make a connection with CenturyLink's network.

  • If the light near the DSL or LINE label is not lit up at all, then the modem is not detecting a signal from the CenturyLink network.
  • A slow blinking green light indicates the modem has found the CenturyLink network but has not yet created a connection, or it has not yet "trained up".
  • A fast blinking green light indicates the modem is in the process of creating a connection with the CenturyLink network, or "training up".
  • A solid green light indicates that the modem has completed the connection, also known as "trained up".


Whereas the DSL light indicates your modem's connection to the CenturyLink network, the INTERNET light indicates your modem's connection to the Internet. If the INTERNET light is either solid green or flickering green, you're in good shape. The green light indicates you are connected to the Internet. A flashing green light indicates that data is being transmitted between your modem and the Internet.

If the light is blinking alternately between red and green, it means the modem is auto detecting the WAN configuration. An amber (yellowish-orange) glow typically indicates the modem is in the process of running through the initial activation process to enable it to get on the CenturyLink network. This is a function that is required before the modem is allowed to connect to the Internet. A red light indicates that either the modem is failing to authenticate on the CenturyLink network (in PPP mode) or the CenturyLink network is not receiving your IP address (in DHCP mode).

(4) ETHERNET 1-4

There will be one Ethernet light for each Ethernet port on the back of the modem. Any Ethernet port that is connected by an Ethernet cable to a device will cause the Ethernet light to come on. If the light is a solid color it means that port is connected. The light will flicker whenever data is being transmitted through the corresponding port.


Your modem will only have a WIRELESS light if it has built-in wireless capabilities. When the WIRELESS light is solid green it indicates that the modem's wireless functionality is turned ON, but no data is being transmitted wirelessly. The green light will begin to flicker when data is being sent and received wirelessly.

If the WIRELESS light is amber (yellowish-orange) it usually means that the wireless functionality is temporarily disabled using the wireless schedule feature found in the modem configuration interface. This functionality may not apply to all modem models.If the light near the WIRELESS label is not lit up at all, then the wireless functionality for the modem is OFF. Find out how to turn it back on.

(6) Model Number

It doesn't get much easier to figure out your modem model than reading it from the front of the modem. Keep in mind the model "number" may actually include any numbers and letters that you may see here. You might also want to take note of the brand of the modem manufacturer. You'll need both the brand and the model number if you want to look up the details of your specific modem.

(7) WPS Button

WPS, or Wi-Fi Protected Setup, is an easy way of connecting wireless devices to your wireless network with a press of a button.

Bottom of the Modem: Sticker with Unique Modem Details

If you aren't able to read your sticker, or if some of these items aren't included on your modem's sticker, then you can connect to the modem's visual interface to find the information.

Model Number

The model "number" does actually include any numbers and letters that you may see here. You might also want to take note of the brand of the modem manufacturer. You'll need both the brand and the model number if you want to look up the details of your specific modem.

Serial Number

The modem's serial number is a code assigned by the manufacturer to uniquely identify each modem. Although it's called a "number," it may actually include letters as well.

MAC Address

The MAC address is a permanent unique identifier used to distinguish your modem from other pieces of hardware across the networks that it interacts with.


The SSID, or Service Set Identifier, may also be referred to as the Network Name or sometimes even ESSID (Extended Service Set Identifier). Typically the SSID is a string of alphanumeric characters and it is case sensitive.

When you try to connect a device to your modem's wireless network, the device will list all of the wireless network names it finds. Typically, it'll find more than one network. In order to connect to your own network and not your neighbor's, you'll need to know the network name (SSID or ESSID) that your modem is broadcasting.

The SSID is the public name of the wireless network being broadcasted by your modem. The SSID listed on your sticker is the factory default.Security Type

Security Type

This is the type of wireless security protocol that your modem uses by default.

Key / Passphrase

The KEY or PASSPHRASE listed on the sticker is your modem's default value.

When you try to connect a device to your wireless network, if security is turned on, you'll be prompted to provide the network KEY or PASSPHRASE. Often times the value on the sticker is what you should enter. However, if the wireless default settings were ever customized, then the default may not work. In some cases, both the customized and the default values will work.

If the default value for the KEY or PASSPHRASE isn't working, and you've forgotten your customized wireless credentials, then your only option is to use the RESET function on your modem to reset your modems wireless credentials to the defaults.


WPS, or Wi-Fi Protected Setup, is a way of easily connecting wireless devices to your wireless network. WPS may use either the PBC (push button configuration) method or the PIN (personal identification number) method. If your modem is configured to use the PIN method, then when you attempt to connect a wireless device using WPS, you will be prompted to provide the WPS PIN.

Modem GUI Address

The modem's visual interface, which allows you to manage the various functions available on your modem, can be accessed by entering this string into the address bar of a web browser, such as Internet Explorer or Firefox. You must be connected to your modem's network in order for the address to successfully find your modem.

Admin Username & Admin Password

Some modems will require this information in order to access the modem's visual interface.

Power Rating

The POWER RATING is listed in the small print of the sticker. This information will tell you the proper voltage and amperage your specific modem requires. If for some reason your modem's power cord is damaged, you should make sure to replace it with a power adapter that matches the modem's power rating.