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NETGEAR - 8 x 4 DOCSIS 3.0 Cable Modem - Black

The NETGEAR CM400 High Speed Cable Modem provides a connection to high-speed cable Internet, up to 340 Mbps. With DOCSIS 3.0 it is 8X faster than 2.0. It is CableLabs DOCSIS 3.0 Certified to work with cable Internet providers XFINITY from Comcast, Spectrum, Cox, Cablevision and more.

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    What's Included

    • Ethernet cable
    • High Speed Cable Modem - DOCSIS 3.0 (CM400)
    • Power adapter
    • Quick install guide
    • Stand

    Ratings & Reviews

    Overall Customer Rating:
    95% of customers would recommend this product to a friend (1723 out of 1832)



    Compatible with cable Internet Providers like XFINITY from Comcast, Spectrum, Cox, Cablevision & more. Call your internet service provider for additional compatibility information.

    Gigabit Ethernet Port

    DOCSIS 3.0 Cable Modem with 1 Gigabit Ethernet port. Fastest wired speeds to connect your router or computer.

    Save on Fees

    Eliminate monthly cable modem rental fees - up to $120 per year.

    Higher Speeds

    Up to 340 Mbps download and upload speed for streaming HD videos, faster downloads, and high-speed online gaming.

    Improved WiFi Connection

    Boosts speed, reliability, & range of WiFi connections.


    8 downstream and 4 upstream channel bonding offers the fastest possible cable Internet speeds during peak hours.

    DOCSIS 3.0

    DOCSIS 3.0 up to 8x faster download speeds than DOCSIS 2.0.

    External Router Needed

    This devices requires an external router for WiFi capabilities. Recommended to pair with NETGEAR WiFi router.

    Customer rating

    Rating 4.5 out of 5 stars with 1832 reviews

    would recommend to a friend



    Most relevant reviews

    See all customer reviews
    • Rating: 1 out of 5 stars

      Garbage--dead after 8 months

      • Verified PurchaserVerified Purchase
      • My Best Buy® MemberMember

      After purchasing this Netgear model, it was not powerful enough for a 2000 square foot townhouse. So it was exchanged for the Netgear C6300 ($150+. Unfortunately because of the exchange, Best Buy is making me review this model instead). The C6300 worked great for 8 months...then suddenly, the internet stopped working. Devices would pick up the network but not work. System reset would not work. So Comcast came out three times and inspected everything. They even reburied an outside line. Still, no internet. Comcast said everything was working according to them! I didn't suspect this modem/router was the issue because all lights were on, and the unit was 8 months old. But finally, the Comcast technician swapped this out for their own equipment...and then the internet worked. The Netgear C6300 had died. Since it was within the year, I called customer service. After registering everything, and waiting forever for them to answer, they said they would not help me because the could not verify it was broken. The Netgear rep needed me to have Comcast re-establish the modem/router so they could check that it had actually failed. Now, do you think I want to call Comcast for them to take off their working equipment, to reauthorize the dead Netgear equipment, just so I can then call Netgear back and they can verify it is dead? Ridiculous. I told them No, I would throw it in the garbage and never purchase Netgear again.

      No, I would not recommend this to a friend

    • Rating: 5 out of 5 stars

      It was a good modem!

      • Verified PurchaserVerified Purchase
      • My Best Buy® Elite MemberElite Member

      Recently I had exchanged this modem for a "Zoom - DOCSIS 3.0 High-Speed Cable Modem - Black" due to internet issues I was having, however this exchange was based on Comcast convincing me the problems with my internet was with the modem -- and not their service -- and they recommended that I return and exchange the modem for another. This didn't fix the issue as the problem was with Comcast, however I will share my experience with this modem since it was a pretty good modem. Basically, it's a Cable Modem and it does its job. It has a nice and sturdy, attractive and sleek look and feel to it. I bought a Netgear Wireless Router to go along with it and they complimented each other very well, especially when standing vertically. This doesn't have built-in WiFi and only has one port to connect to a computer or router. It's extremely simple to setup. In fact the only amount of complexity with using this modem is calling up Comcast to provision it for use, but even then it takes about 10 or so minutes. Just be sure to have your MAC Address on hand so you don't have to move the router around again trying to get to it. The admin interface on this device is either for changing your modem's password and viewing logs, nothing special. The only problem I had with the modem is when Comcast's signal dropped or was disrupted, the modem would take a long time trying to reestablish a connection. Manually power cycling would connect much quicker. If it wasn't for Comcast's inability to fix issues on their end, I'd have kept this modem; like I said, I exchanged it for another because they recommended I did, even though the problem was them, not Netgear. I do recommend this modem!

      I would recommend this to a friend

    • Rating: 5 out of 5 stars

      Netgear CM 400 DOCSIS v3.0 Cable Modem

      • Verified PurchaserVerified Purchase

      I bought this in April 2015 to replace a CM 100 to get the recent Time Warner Cable speed upgrades on their L.A. system. It is on their list of approved modems, so I bought this to save the monthly rental fee. TWC has a feature on their website that will allow you to update your modem, but it just doesn't work right (either for user OR TWC supplied modems). After a phone call to their "Customer Care" people, I was able to read them the MAC address of my old modem & the new one (on the box) and the rep manually updated TWC's database. It has been great ever since! This CM 400 modem has been flawless since installation, just like the CM100 I had for abut 3 years. Keep in mind that this is a modem only, and not a "combo" modem & WiFi unit. Since I already had a separate WiFi setup, I only needed the modem updated which is the cheaper & better way to go. This model supports all of the current (6/2015) TWC plans up to and including "Ultimate 100" (100 Mb/s). This should be fast enough for just about 99.9% of the user base. If you need more speed than that, it starts to get really expensive to go faster both in monthly bills and for faster equipment. As an example, I am running the 50 Mb/s speed, and we have an Apple TV upstairs, a BluRay/NetFlix downstairs, 2 college students at home, and a small home office setup for an IT consultant (me) with everything running happily 24/7. I would buy this again! It will pay for itself by Christmas.

      I would recommend this to a friend

    • Rating: 1 out of 5 stars


      • Verified PurchaserVerified Purchase
      • My Best Buy® MemberMember

      After installing my new Modem as per the provided instructions, I powered it up and was dismayed to see that the indicator LEDs were flashing amber. Neither the provided instructions nor the downloadable user manual made any mention of flashing amber lights, so I subsequently contacted Netgear tech support. Following a protracted phone conversation, the tech support supervisor agreed that the Modem was defective [even when I assured him that the Modem was transmitting data] and that he would arrange for a 'hot swap'. So far, so good. The second day following my conversation with tech support, FedEx delivered a replacement Modem. I hooked it up only to have the same problem occur...flashing amber LEDs but no data transmission this time. Disgusted with Netgear products, I went to a local store and bought a Motorola (Arris) Modem. When I subsequently contacted my ISP tech support with yet a third Modem MAC ID change, the tech support guru told me that mine was the 8th report of defective Netgear Modems that he had dealt with, which certainly does not speak well for Netgear equipment.

      No, I would not recommend this to a friend

    • Rating: 1 out of 5 stars

      Stopped working and can't update firmware

      • Verified PurchaserVerified Purchase
      • My Best Buy® MemberMember

      This modem worked well for the first nine months, but they sent an email a couple weeks ago saying that there was an important security firmware update that needed to be installed, but when I tried to navigate to the install file, it told me that it has to be "pushed" out by my ISP. I called them, and they said that because it isn't one of their modems, they can't update it. I have to get the update from NetGear. NetGear does not have tech support after the first 90 days after purchase (you have to pay $50 for help!), so I posted in the forums to see if there was another way to get the update. There isn't. So I have a non-functional modem. I had to buy another one--this time from my ISP, so I don't have this problem again. NetGear should be ashamed. No free tech support for their products is ridiculous.

      No, I would not recommend this to a friend

    • Rating: 4 out of 5 stars

      Modem works well

      • Verified PurchaserVerified Purchase
      • My Best Buy® MemberMember

      I previously had a dlink modem that was about 7 years old. I decided to upgrade to take advantage of a faster internet connection I now have, and as I had already purchased a Netgear wireless router about a year ago, I decided to get a Netgear modem as well. I had some trouble with the initial setup as my modem worked directly connected to my laptop, but would not work with the wireless router. I called Netgear and found out that they only offer complimentary support service for 12 months. As I purchased my router over a year ago, I was out of luck. After I expressed my frustration with this rule and indicated that I was a loyal Netgear customer and just purchased another one of their products, the agent agreed to offer me complimentary assistance and helped me to reset my model and router so that they would work together. After that my modem has worked well. I have an up to 75 Mbps internet plan from Comcast and have an actual download speed of about 30 Mbps when tested over the wireless connection (I have not tested through the ethernet connection yet).

      I would recommend this to a friend

    • Rating: 3 out of 5 stars

      Not Recommended

      • Verified PurchaserVerified Purchase
      • My Best Buy® MemberMember

      I bought this new and installed it and immediately had my wifi speeds drop dramatically (75mbps with Comcast wifi modem to 30 mbps with Netgear wifi modem—speeds didn't change even when hardwired to computer). I initially blamed Comcast and they sent out a tech who was super informative. He explained that he's been seeing some glitches with the Netgear wifi modems lately and that my new modem was not locking onto available channels which is why it was slower than it should be. He suggested a different brand (Motorola or Arris). I replaced with an Arris modem and added Eero for wifi. The new modem was able to lock onto available channels and speeds went up to 175mbps. I'm giving it 3 stars because it operated. It just didn't operate well and it's possible i just got a bad one.

      No, I would not recommend this to a friend

    • Rating: 1 out of 5 stars

      Product is not good


      I bought Netgear CM400 model on Thanksgiving day and installed on 12/01 it did not work. Continuous trouble shooting with Netgear 1st level support, 2nd level and supervisor, there is defect with this product alone, so I have returned the product and took a new one of the same model and installed on 12/04 it worked for 10 days then it started the issue. After call with the Netgear 1st level support, 2nd level and supervisor came to know that there is defect in hardware for the model itself which they have fixed and available only in their warehouse, and not have been distributed to the retail units. If the product is bought across any retail units still it may have issues.

      No, I would not recommend this to a friend

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