The ARRIS DOCSIS 3.0 8×4 Cable Modem CM820A features high speed data access to cable service subscribers for both home & business. The CM820 meets the productivity needs with the speed and performance found only in the 8×4 bonded channel cable environment along with industry-leading ARRIS reliability. With the CM820A offers data services at speeds over 300Mbps to their subscribers to compete against VDSL and fiber to the home threats, as well as provide a platform to deliver competitive high capacity commercial services to businesses.
Is the CM820 compatible with Comcast?
Yes! This model is compatible with Comcast Xfinity in most areas. Please contact your Comcast office or their customer service to confirm compatibility in your area with your service plan.
Does the Arris CM820A have WiFi?
No. This model is just a cable modem and only supports wired internet service. Click here to check out our list of routers that pair perfectly with this model!
Beth –
I was told by Comcast to replace my outdated modem (that I owned.) I purchased this Arris model, and couldn’t be happier. It did not come with installation instructions however, so I emailed the supplier (on a Saturday) and they replied same day with installation instructions. Impressive! I wanted to try to install it on my own, without calling Comcast. However, I found out halfway through the step by step process that I needed to contact Comcast first, in order to give them the model number of this new modem, so that the activation would be successful. No worries…the internet provider agent completed the installation remotely, and I am up and running! Now I am finally enjoying the internet speed and strength that I have been paying for, and not receiving with the old, outdated modem.
Mr. Cheap Skate –
I was getting notices from Comcast that my old Motorola cable modem was not giving me the benefits of higher bandwidth speed…which I ignored for the past year assuming they were just trying to get me to spend more on a faster speed plan. Then recently I started having intermittent internet loss, so I decided to buy this modem . While waiting for it to arrive I upgraded the firmware on my netgear N300 wireless router and it seemed like that gave me a stable internet signal. When the modem arrived I set it up and to my surprise it increased my speed from 7 to 12 .
The reason for not giving 5 stars is the the seal of the plastic bag that contained the modem was opened, but the modem itself was new and the cable also. There were no instructions that came with it, but I followed the instructions on comcast website and was able to easily get it set up without calling comcast.
Samwise –
After trying out 3 different cable modems, I’m somewhat convinced this Arris CM820A is the one to get for Comcast. My situation is we weren’t getting the speed that we signed up, and our connection also drops off periodically. After checking Comcast’s approved modem list, I purchased 3 different ones to test, and this Arris one seem to be the most stable.
It’s been 2 months since we replaced our old 3.0 modem with this one, and we only had to reboot twice in that span. What I like is each time when we noticed a slowdown in download/upload, the Arris would show a different color light on the corresponding stream, so there is an accurate indication system.
J. Salzenstein –
Works great, but didn’t come with instructions on how to set up… I had to search for the manual online, which wasn’t crazy difficult, but took more time than it should have. (You also need to then call your cable provider to activate, which was also an exercise in frustration.)
George R. –
Very easy self-installation when I added internet to my Comcast account. Basically you just hook it up to the cable and router, although depending on the type of router you may have to tweak its settings so that it correctly assigns local IP addresses to your various devices. Comcast makes you order a self-installation kit for $10-$20, which contains just a generic Ethernet cable and standard coax cable. They don’t tell you what is in the kit, and you don’t have the option of not paying for it. Ripoff.
Babbity Rabbity –
Got a message from Comcast saying the modem they originally gave me could no longer support my internet speeds, so instead of upgrading for fear of hidden fees and to ditch the $10.00/month fee I pay for leasing theirs, I bought my own. So far, it’s been working great. No complaints.
Tseg –
I got the notice months ago from Comcast that my tried and true tiny Arris that looks like the CM820A but many generations earlier (but still DOCSIS 3.0) was outdated and they wanted to “upgrade” me to that huge modem/wifi unit they have been putting in market (Arris TG862G). I had been renting the modem for years… because the company I work for pays the bills. The new unit was horrible. I kept dropping wifi, both from the Comcast unit as well as the Netgear wifi router I had connected to it. I never had the issue with the old Arris unit.
I sprung for the CM820A and it’s as good if not better than the unit I retired months ago… At under $80 this is a no brainer vs. renting a Comcast monster unit that is glitchy. I will mention I had to call into Comcast to have them activate it as the online registration was not taking. I’m not sure of the issue, but it took Comcast about 45 minutes and multiple tries to get the switch to take. With that said, they were very patient and accommodating. I got a little nervous as the unit number on the front just says CM820 (not Comcast approved) but the decal underneath states CM820A – Comcast approved.
Boston Mom –
Bought this because Comcast notified me that my old modem (which I had been renting from them)was outdated. Had to go on the Arris website to download installation instructions. Installation was simple. I did need to call Comcast and tell them I was making the change, just to be sure they would stop billing me for the rented modem. Haven’t done a speed test, but my internet is working well. Recommend buying this modem and saving yourself the $10 per month rental fee at Comcast!
V0X –
GREAT little modem that works well for Comcast. I have the Extreme 150 Mbps service and my computer connected to the router and this little gem is showing throughput of 180 Mbps. This modem is also the same modem that Comcast leases to customers for $10.00 a month and has a three star certification on the Xfinity MyDeviceInfo page. I replaced a Motorola SB6141 that I JUST purchased at Walmart for this modem. The SB6141 just hit Comcast’s “end-of-life” which means they’ll no longer “support” them, but you can still use them. Since I was within the 45 day return window, I played it safe and opted for the Arris CM820a.
TechCraver –
Comcast sucks, this modem is great. Sticking it to the “man” by not paying $$$ to Comcast to rent a modem. Only catch is they are forcing you to buy new modems every year practically because of their bogus “end of life” modems. Keep an eye out because they add new ones every year. This is all just ways to make you spend more money! If they are forcing you to buy a new one, you might as well save a little money and give it to another business then Comcast.
Side note, make sure you do the self-installation when you sign onto their Internet services. They’ll try and charge you $10, but some workarounds are trying to tell them you are “picking up their validation code at the store”. Be weary of your bill since they hate people who have their own modem and try and tack on all sorts of charges to make up for their modem rental loss.
Can’t wait until there are some competitors and not monopoly in this industry. Or just move to a Google farm and get 1gb dl/ul for locals…
S. Jackson –
It works. My internet still drops, but I’m not sure if that’s on my end or Comcast. I still have to power cycle it or have Comcast reboot on their end several times a week, but this is an improvement from our last one!
Techie –
I ordered this CM820A Modem to replace the “rented” one that I was paying 10 dollars a month for through my Internet provider. I have been using it now for a little over a week! So far its performing flawlessly as expected!!
Thanks Techa Distribution for a great product!!
Koz –
Paid for itself in 3 months when I bought it at discount on Warehouse Deal. I subscribe to 75 mbps service and speedtest regularly shows me pulling over 80 mbps when on a LAN. I think this modem is rated up to 100 mbps, at least. Check the comcast website for compatibility for the plan you are using. Otherwise, it’s literally plug and play after you call in your MAC address number to Xfinity.
Customer –
I’m very pleased with this product. We weren’t getting the amount of internet speed we were paying for because we had an end of life device. With this our internet sped up to 175mbps.
Bob Kerr –
This modem was exactly what was needed to install a new Comcast cable service. Purchased this ahead of a the Comcast tech doing the install (hired Comcast because we had some cable to run in the house). The modem arrived on time, and the tech had no problems installing/configuring. The Internet connection is working perfectly.
Michael D McCoy –
Comcast had a hard time getting it to work on their end but that was due to incompetence on their part not the hardware. This product has worked perfectly once Comcast did their part. ( I’m a SCCM Admin BTW so I know of what I speak on this. )
CJ –
Bought the same model modem I had which burned out due to an issue with the Comcast splitter in my home — it got wet, the modem tried and tried and tried and finally died — it gave up on connecting to the internet. Never an issue till that accident, and no issues since installing the replacement.
ND –
This modem replaced my Comcast rental which was $10/month. I’ve noticed better speeds from this modem over the standard issue Comcast device without changing any other variables (i.e. router, placement in the home, devices used to access wifi.)
Mark in Seattle –
This cable modem initially appeared to work well with Comcast. It then started to only intermittently forward DNS requests causing loss of Internet. I purchased a different cable modem (Motorola) and all is good again. The issue appears to be the software Comcast downloads into the box, as the rest of my setup (NetGear Wireless Access Point) works fine with both the Comcast rented CM and the Motorola.
Nova Scotia –
Why pay $10 month to rent from Comcast? 18 months and I have had zero problems. It’s alread paid for itself. Buy your own wireless router and plug it into this. Own what you pay for. Renting is for suckers.
Paulo R. Crestani Jr. –
The modem is good, but I bought it used and I discovered later that its serial number was registered in Comocast as the equipment belonging them, and I was charged as if I was renting it. It required me to go after Comcast customer service twice and more than 1 year later they agreed to give me back the rents the had charged me monthly, which was enough for me to have bought several brand new modems like this. It seems to be a common case with used modems.
Naomi –
Product was very easy to setup once I realized I should connect my computer directly to the modem to complete setup.
If you’ve ordered this to replace a modem/gateway you’ve been leasing from Xfinity, your instinct may be to try to set it up using the xFi app on your phone.
The xFi app doesn’t recognize this model and gives a recommendation to contact support for help.
This modem paired with a dual band router I had on hand is an adequately-performing replacement for the Xfinity leased model I was using before.