What you need before you start

Your Xfinity modem connects to two things: the coaxial cable from your wall (the thick cable with a metal connector) and power. Before you plug anything in, gather these items. You will need the coaxial cable that comes from your wall outlet — this is the same cable that would connect to a cable box or TV. You will also need the power adapter that came with your modem, or a standard power outlet within six feet of where you want the modem to sit.

Check the back of your modem for the label with your account number and MAC address. You may need this information later, so take a photo or write it down. If you do not have the original power adapter, any standard modem power adapter rated for your modem model will work — check the model number on the bottom or back of the unit.

Your modem should be placed in a central location in your home, away from metal objects, microwaves, and cordless phones. A shelf or table near where the coaxial cable enters your home works best. Do not place it in a closet, cabinet, or on the floor — these locations block the signal and cause connection problems.

Key Takeaways

  • Connect the coaxial cable from your wall to the port labeled "Cable In" on the back of the modem, then plug in the power adapter.
  • Wait three to five minutes for the modem to fully start up — you will see lights change from red to green on the front panel.
  • Once the lights stabilize, your modem is connected to Xfinity's network and ready for your router to connect to it.
  • If lights stay red or amber after ten minutes, restart the modem by unplugging it for 30 seconds, then plugging it back in.
  • You can check your connection status through the Xfinity app or by calling Xfinity customer service if the modem does not come online.

Connecting the cables

Locate the port on the back of your modem labeled "Cable In" or "Coax In" — it is usually the largest port and has a threaded metal connector. Take the coaxial cable from your wall and screw it firmly into this port by hand. You should feel it tighten; do not use a wrench or pliers, as this can damage the connector. The cable should be snug enough that you cannot easily pull it out by hand.

Next, plug the power adapter into the modem's power port — this is a small round or rectangular port, usually on the side or back. Then plug the power adapter into a wall outlet. You should see lights on the front of the modem begin to turn on. Do not be alarmed if they are red or amber at first; this is normal during startup.

Waiting for the modem to come online

After you plug in the power, the modem needs time to connect to Xfinity's network. This process usually takes three to five minutes, but can take up to ten minutes on the first connection. During this time, the lights on the front will change. You may see a power light come on first, followed by other lights turning on or blinking.

Watch the front panel of the modem. Most Xfinity modems have lights for power, internet, and downstream/upstream signals. When the modem is fully connected, the internet light (usually labeled "Online" or "Internet") will be solid green. If you see a solid green light, your modem is connected to Xfinity's network and is ready for your router to connect to it.

If the lights are still red or amber after ten minutes, the modem may not have connected. This can happen if the coaxial cable is loose, if there is a service outage in your area, or if your account is not yet active with Xfinity. Check that the coaxial cable is hand-tight, then wait another five minutes.

Restarting the modem if it does not connect

If the modem does not show a solid green internet light after fifteen minutes, restart it. Unplug the power adapter from the wall outlet and wait 30 seconds. While you wait, you can also unplug the coaxial cable from the modem and check that it is not bent or damaged. After 30 seconds, plug the power adapter back in, and if you unplugged the coaxial cable, plug that back in as well.

The modem will go through the startup sequence again. This time, watch for the lights to change more quickly — a restart usually takes two to three minutes. If the internet light turns solid green this time, the restart worked and your modem is now connected.

If the modem still does not connect after a restart, the issue may be with your Xfinity account, a service outage, or a problem with the line coming into your home. At this point, you will need to contact Xfinity customer service. Have your account number and the MAC address from your modem label ready when you call.

Connecting your router to the modem

Once your modem shows a solid green internet light, it is ready for your router to connect to it. Your router connects to the modem using an ethernet cable — a thin cable with plastic connectors on each end. Look for the port on the back of the modem labeled "Ethernet" or "LAN" (usually there are one or more of these ports). Plug one end of the ethernet cable into any of these ports.

Plug the other end of the ethernet cable into the port on your router labeled "WAN," "Internet," or "Uplink" — this is usually a different color from the other ethernet ports on the router. Once the cable is connected, your router will begin connecting to the modem. This usually takes one to two minutes. You will see lights on both the modem and router change as they communicate.

Checking that everything is working

After your router connects to the modem, you should see lights on both devices stabilize. The modem's internet light should remain solid green, and the router should show a solid light indicating it is connected to the internet. You can now connect your devices to your router's wireless network or to the router using ethernet cables.

To verify everything is working, try connecting a phone, laptop, or tablet to your router's wireless network and opening a web browser. If a webpage loads, your connection is working. If you cannot connect or pages do not load, restart both the modem and router by unplugging them for 30 seconds, then plugging them back in.

What to do if you have problems

If your modem connects but your internet is very slow, restart both the modem and router. Slow speeds can also happen if your router is too far from where you are using it, or if there are many devices connected at once. Move closer to the router to test if distance is the issue.

If the modem will not connect at all even after multiple restarts, check whether there is a service outage in your area. You can check this through the Xfinity app or website, or by calling Xfinity customer service. If there is no outage, the coaxial cable from your wall may be damaged, or your account may not be active yet. Xfinity customer service can help you troubleshoot these issues.

Frequently Asked Questions

How long should it take for the modem to show a green light?

Most Xfinity modems show a solid green internet light within three to five minutes of being powered on. If it takes longer than ten minutes, restart the modem by unplugging it for 30 seconds. If it still does not connect after a restart, contact Xfinity to check whether your account is active or if there is a service outage.

Can I use any ethernet cable to connect the modem to the router?

Yes, any standard ethernet cable will work. The cable does not need to be a special type or brand. If you do not have an ethernet cable, you can also connect your router wirelessly to the modem, though this is less common with Xfinity modems and routers.

What do the different colored lights on the modem mean?

The power light shows the modem is on. The internet or online light shows the modem is connected to Xfinity's network — this should be solid green when everything is working. Other lights show signal strength and data flow. Red or amber lights usually mean the modem is still starting up or is not connected yet.

Do I need to do anything with the modem after it connects?

Once the modem shows a solid green internet light and your router is connected, you do not need to do anything else with the modem. It will stay on and maintain your connection. You do not need to restart it regularly unless you have connection problems.

What if the coaxial cable from my wall is too short?

You can buy a longer coaxial cable at any electronics store or online. Make sure it is rated for cable internet use. Screw it into the "Cable In" port on the modem the same way you would any coaxial cable. Avoid running the cable through walls or under carpets, as this can damage it.