NETGEAR CM400 DOCSIS 3.0 Cable Modem: features, specs and who it suits

The NETGEAR CM400 (model CM400-100NAS) is a cable modem. It connects a home to a cable internet service and passes the connection on through a single Ethernet port. It is a modem only, with no Wi-Fi of its own, so it is meant to be paired with a router. Here is what its specs mean and what to confirm with your provider.

What a cable modem does

A cable modem translates the signal on your coaxial cable into a standard Ethernet connection. Providers often supply one, but a customer-owned modem is an option on many networks. The CM400 is a customer-owned type. The brand says it is certified by CableLabs, the industry body that tests cable equipment, and it lists compatibility with US cable providers such as Xfinity from Comcast, Spectrum and Cox.

DOCSIS 3.0 and channel bonding

DOCSIS is the standard cable networks use for data. NETGEAR says DOCSIS 3.0 delivers speeds eight times faster than DOCSIS 2.0. The key feature is channel bonding, where the modem uses several channels at once instead of one. The CM400 has 8 downstream by 4 upstream bonded channels. NETGEAR quotes speeds of up to 340Mbps for download and upload, which is a maximum under ideal conditions rather than a promise for every home.

Newer standards exist, such as DOCSIS 3.1, which are designed for faster tiers. NETGEAR positions this model for cable plans up to 100Mbps, so match it to your plan's speed.

One gigabit Ethernet port

The modem has one Ethernet port with auto-sensing, which means it negotiates its speed with whatever it is plugged into. A single port means one device connects directly, usually a router. NETGEAR notes that a separate router is required for Wi-Fi. If you want several wired devices, they connect through the router or a switch.

NETGEAR describes the CM400 as suited to streaming HD video, downloads and online gaming, which are all things that benefit from a stable connection. It lists 64MB of memory.

What it doesn't do

The listing says the modem is not compatible with bundled voice services. If your provider supplies home phone service through the same equipment, this modem won't handle it. It also has no built-in Wi-Fi or router functions.

Size

The modem measures about 8.5 x 7.2 x 2.0 inches (roughly 22 x 18 x 5 cm) and weighs 1.1 lb (about 0.5 kg), which is small enough for a shelf or a media cabinet near the cable outlet.

Who it suits

It suits a household that owns its own router, has a cable plan within the modem's range and wants to own its modem. It is less suited to people on faster tiers or those with bundled phone service.

What to check before you buy

• Provider approval: check that your provider lists the CM400-100NAS as supported on its network.
• Plan speed: compare your plan's speed to the 100Mbps the model is intended for; NETGEAR quotes up to 340Mbps maximum.
• Voice service: confirm that you don't rely on bundled phone service through your modem.
• Router: you will need a separate router or Wi-Fi system.
• Activation: most providers need you to register the modem's details, so keep the packaging and serial numbers handy.
• Warranty and support: check the terms for your region in the documentation.

The short version

• A DOCSIS 3.0 cable modem with 8x4 channel bonding.
• NETGEAR quotes up to 340Mbps and positions it for plans up to 100Mbps.
• One gigabit Ethernet port; a separate router is required for Wi-Fi.
• Listed as compatible with Xfinity, Spectrum and Cox, but not with bundled voice services.

Bloiq is reader-supported. Some links may earn us a commission; it never affects what we write. How we make money.