This article covers DOCSIS 3.0 High Sp Cable Modem.

Overview

The NETGEAR CM400 is a DOCSIS 3.0 cable modem designed to eliminate monthly rental fees while delivering reliable internet connectivity. It supports up to 340 Mbps download speeds using 8x4 channel bonding (8 downstream, 4 upstream), making it suitable for HD streaming, online gaming, and general browsing.
This modem is compatible with major US cable providers such as Comcast Xfinity, Spectrum, and Cox. It does not include Wi-Fi, so you'll need a separate router for wireless devices. The CM400 is a cost-effective solution for users who want to own their hardware and save up to $156 per year on rental fees.

Connectivity & Compatibility

The CM400 offers one Gigabit Ethernet port for wired connections. It is DOCSIS 3.0 certified, which is backward compatible with DOCSIS 2.0/1.1 networks. However, it does not support voice services (VoIP). Before purchasing, verify that your cable provider allows customer-owned modems and that the modem's MAC address can be registered on their network.
Note: This modem is designed primarily for North American cable systems. Compatibility with Japanese cable TV services (e.g., J:COM) is not guaranteed. Check with your local provider for supported modem models.

Product Info

The NETGEAR CM400 was released around 2015 and is positioned as an entry-level to mid-range cable modem. It is widely available on Japanese online retailers for approximately ¥11,000 (new) or less (used). The package includes the modem, an Ethernet cable, and a power adapter. The standard warranty is one year.
Market positioning: This is a DOCSIS 3.0 modem optimized for internet plans up to 340 Mbps. For gigabit plans, you'll need a DOCSIS 3.1 modem. The CM400 is a solid choice for budget-conscious users who don't need the latest speeds.

Best Use Cases

  • Users paying monthly modem rental fees: If your ISP charges $10-15/month for a modem, the CM400 pays for itself in under a year. Ideal for Comcast, Spectrum, and Cox customers in the US.
  • Users who already have a Wi-Fi router: Since the CM400 is a pure modem (no routing, no Wi-Fi), it's perfect for those who want to keep their existing router setup.
  • Budget or light internet users: For plans under 340 Mbps, the CM400 delivers sufficient performance for streaming, email, and social media. Not recommended for heavy gamers or 4K streaming households that need >500 Mbps.
  • Not suitable for: Users with gigabit internet plans, those needing voice service, or anyone using a Japanese cable provider that doesn't support DOCSIS 3.0 modems.

Product Disclosure (Amazon)

  • Manufacturer: NETGEAR
  • Seller: Amazon US
  • Fulfilled by: Amazon US
  • ASIN: B00MN2EUEA
  • Note: This article covers a manufacturer-made product based on Amazon listing details.