The Arris CM820A is a cable modem primarily used with Comcast & other US-Based cable internet providers. This model features 8×4 channel bonding and supports wired download speeds of up to 343Mbps. Here’s our guide on how to activate the CM820, set it up, log in to it’s settings panel & more! If you don’t see the answer to your question or need clarification, feel free to leave us a comment!

How to Activate Arris CM820

The easiest way to activate your modem is to call your internet service provider using the phone number found on your internet bill and have them walk you through the activation process for your device. It does help speed things up on your call if you have your modem plugged in and ready to activate before you call your provider.

  1. Plug in and power on your Arris CM820.
  2. Screw in the coaxial cable into the port on the back of your modem.
  3. Wait 1 hour for firmware updates to be completed. This ensures that your device has the most recent and easy to activate firmware available. If the modem was recently in service, you can probably skip this step.
  4. After 1 hour, call your internet provider using the phone number found on your internet bill.
  5. Follow the steps provided by your internet provider and complete the activation.

How to Reset Arris CM820

Resetting your Arris CM820 can help resolve a large number of common networking problems, and can also be vital when activating a modem that was used previously by someone else or when doing troubleshooting for a common networking issue. Knowing how to reset your modem is vital as it can save you time and money from needing to call your internet provider’s technical support, miss work for a service call or spend hours doing troubleshooting on your weekend. Here’s how it’s done:

  1. Plug in and power on your Arris CM820.
  2. Locate the reset button hole on the back of your modem where all the ports are located.
  3. Press and hold down the reset button for 30 seconds with a paperclip or toothpick.
  4. After 30 seconds, release the reset button and allow the modem to power cycle itself and finish resetting.
  5. Allow 2-3 minutes for your device to power cycle before reconnecting your WiFi router.
Arris CM820A DOCSIS 3.0 Cable Modem

Arris CM820 Login Instructions

The Arris modem CM820 manual would not be complete without instructions on how to login to the admin settings panel. Logging into your Arris CM820A takes almost no time and allows you to access the modem’s internal settings page. This allows you to view your network status and adjust security and other settings inside of the modem. Since the CM820 does not have built-in WiFi, this feature is not used too often, but can be helpful to know how to do if you’re configuring a more advanced setup.

  1. Plug in your Arris CM820 modem and wait a few minutes for it to power on completely.
  2. Connect an Ethernet cable directly from the port on the back of your modem into your computer or laptop.
  3. Open an internet browser (we prefer Google Chrome, Firefox or Safari) and type in into the web address or URL bar at the top of the page.
  4. You may be directed to the System Status page immediately, OR you may be asked to log in first. Here are the login credentials used by most Arris devices:
    • username: admin
    • password: password

Using A WiFi Router with CM820

The Arris CM820 is just a cable modem and does not have any wireless built-in. If you need WiFi (who doesn’t?) you’ll need to hook up a separate wireless router to your setup to get online wirelessly. Luckily, unlike modems, routers are all pretty much universally compatible with all modems.

Connecting to Your WiFi

To hook up your new wireless router to your CM820, just plug an Ethernet cable into the single Ethernet port on the back of your modem and have the other end go into one of the yellow or grey Ethernet ports on the back of your wireless router. Make sure everything’s plugged in and powered on, and you’ll be good to go.

Most wireless routers that are available for residential use will have the wireless connection information printed on one of the stickers on the bottom or back of the device. Consult these stickers to log into your WiFi initially, then if you want you can change the wireless network name (SSID) and password, add a guest network, set up parental controls, etc. We recommend finding a router that is at least slightly more powerful than your modem. So for this modem, for example, we’d recommend that you pick up something with speeds of at least 400 Mbps, just to ensure you’ve got ample wiggle room on your speeds.

Did we answer all your questions about the Arris CM820A Cable Modem? Let us know in the comments, or leave your own questions for our technicians to answer!

3 thoughts on “Arris Modem CM820 Manual & Activation Instructions

  1. John says:

    No. How do you actually ACTIVATE it???

    1. ModemGuides says:

      Hi John,

      I just had our support add a section for you on here about how to activate this model specifically. Activation is very easy generally, and most of our customers have more problems getting this model connected to wifi than they do with getting their internet activated. We hope this finds you well!

      – MG Support

    2. Cable Guy says:

      Call your internet provider and give them the CM MAC address on the bottom of the modem and tell them you want to activate the modem to have internet access.

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