1 / 2
TechGear
Real discussions from product enthusiasts
Comcast Xfinity Ends SB6121 Support
Users are discussing Comcast's decision to de-list the ARRIS SB6121 modem, with official support ending in December 2022. While some users report it still works for lower speeds up to 75 Mbps, many are advised to upgrade to newer DOCSIS 3.0 or 3.1 models for continued service.
SB6121 Limits Speeds on Plans Over 100 Mbps
Multiple discussions highlight the SB6121's 4x4 channel bonding as a bottleneck for internet plans exceeding 100 Mbps. Users report experiencing significantly lower speeds than provisioned and often upgrade to modems like the SB6190 for better performance and stability.
Frequent Drops Plague SB6121 Users
Users frequently report experiencing intermittent internet connection drops and modem reboots. Troubleshooting often points to signal issues, T3/T4 timeouts, or potential hardware aging, prompting many to consider replacement for more reliable connectivity.
Power Supply Swap Fixes SB6121 Reboots
For users experiencing frequent reboots or connection issues, replacing the original power supply adapter has sometimes resolved the problem. This suggests that aging power bricks can cause instability, rather than an inherent modem hardware failure, offering a potential fix for some users.
Expert answers based on real user experience
Comcast confirmed it is no longer supported as of December 2022 and is not listed on their approved modem page. While some users report it functioning for speeds up to 75 Mbps, it's advisable to check your specific ISP's compatibility list. For reliable service on plans around 100 Mbps or higher, providers generally recommend DOCSIS 3.0 modems with more channel bonding or DOCSIS 3.1 models to avoid potential speed limitations and support issues.
r/Comcast_Xfinity
The SB6121 features 4 downstream and 4 upstream channels, providing a theoretical maximum throughput of approximately 152 Mbps. However, real-world performance is typically constrained to around 120-140 Mbps due to network overhead and ISP provisioning. Users with internet plans exceeding 100 Mbps often find this modem becomes a significant bottleneck, resulting in speeds below their subscribed tier or experiencing intermittent connection stability issues.
ARRIS
Get notified when the price drops
Key features: Compatible with Time Warner Cable, Charter, Cox, Cablevision, and more, Not compatible with Verizon FiOS or AT&T U-verse, no longer approved by Comcast Xfinity, Requires Cable Iternet Service, if not sure your provider is CABLE call them to confirm, BROWN BOX models NOT VALID for this item when sold as New, should report to Amazon immediately and RETURN to Seller, Wired modem only, does NOT include WIFI Router or VOIP Telephone adapter. Gigabit Ethernet port to connect to computer or Router for fast downloads..
ARRIS
ARRIS SURFboard SB8200 DOCSIS 3.1 Multi‑Gig Cable Modem | 2 -1Gbps Ethernet Ports | Works with Xfinity, Cox, Spectrum | For Cable Internet Plans up to 2Gbps | Modem Only, Router Required
Motorola
ARRIS SURFboard SBG6580 DOCSIS 3.0 Cable Modem/ Wi-Fi N300 2.4Ghz + N300 5GHz Dual Band Router - Retail Packaging Black (570763-006-00)
SIMPLIHOME
SIMPLIHOME Harrison Coffee Table Storage Ottoman - 36 inch Wide Upholstered Vegan Leather Square Lift-Top Ottoman in Crimson Red, Transitional Ottoman for Living Room with Hidden Storage
r/HomeNetworking
Users frequently report issues like connection drops occurring up to 4 times daily and unexpected modem reboots. Common contributing factors identified in discussions include T3/T4 timeouts, unstable upstream power levels, or degraded signal quality from the ISP. For modems around 8-10 years old, these symptoms can often be traced back to an aging power supply brick or internal component degradation, leading to intermittent hardware faults that affect overall stability.
r/HomeNetworking, r/techsupport
The modem's internal status page, accessible via its IP address, offers crucial diagnostic metrics. Users can view detailed signal information, including downstream power (dBmV), SNR (dB), upstream power (dBmV), and frequency. It also logs critical events like T3 and T4 timeouts, which are key for troubleshooting connection stability problems with your Internet Service Provider. This page is primarily for monitoring and does not allow for configuration changes.
r/HomeNetworking
For electronic devices like the SB6121, components such as electrolytic capacitors within the power regulation circuitry are prone to degradation over 10 years of continuous use. Factors like heat cycles and power fluctuations can accelerate this aging process, potentially leading to instability, increased error rates (T3/T4 timeouts), or complete failure to power on. While individual component lifespans vary, this age suggests a higher probability of such age-related failures compared to newer hardware.
Expert analysis
A 10 dB downstream signal loss can significantly reduce the signal-to-noise ratio (SNR) for each of the 4 bonded channels, potentially causing data errors and slower speeds. With upstream noise at -45 dBm, the modem will struggle to maintain stable upstream communication, frequently resulting in T3/T4 timeouts and connection drops. The limited 4x4 channel bonding means there's less redundancy and error correction capacity compared to modems with more channels, making it more susceptible to these signal impairments.
Expert analysis
