Why you should trust this review
I have used cable modems from every major manufacturer over the past 12 years and have personally moved between four ISPs and six different modem-router combos. The MB8611 was bought at retail in November 2024; Motorola did not provide a unit. Testing happened on a Comcast Xfinity 1.2 Gbps plan for 14 months, then on a Cox 1 Gbps plan for 4 months after a move.
This is the modem I currently use as my primary, and it has saved me roughly $200 in rental fees so far.
How we tested the MB8611
- 13,100 logged hours of uptime over 18 months across two ISPs
- Throughput tested via fast.com, speedtest.net, and iPerf3 to nearby servers
- Stability monitored with PRTG and the modem’s own diagnostic page (192.168.100.1)
- Compatibility validated by transferring service from Comcast to Cox without modem replacement
- Power draw measured with a Kill A Watt P4400
- See our methodology for full protocol
Who should buy the MB8611?
Buy it if:
- You are on a 1 Gbps or 1.2 Gbps cable plan and currently rent a modem
- Your ISP charges $10+/month for modem rental
- You have or plan to buy a router with a 2.5 GbE WAN port
- You want a modem and not a modem-router combo
Skip it if:
- You are on a 2 Gbps+ cable plan, the Nighthawk CM2000 is the better choice
- You are on fiber or DSL (this is a cable modem)
- You want a modem-router combo for one less device
Throughput: full plan speed
On Comcast Xfinity 1.2 Gbps, fast.com consistently returned 1.16 to 1.21 Gbps download and 36 to 41 Mbps upload (the upload limit is the plan, not the modem). On Cox 1 Gbps, the modem returned 940 to 980 Mbps reliably. The 2.5 GbE Ethernet port means a modem-side bottleneck is not an issue at these speeds.
Stability: 18 months and counting
The modem’s diagnostic page logged zero T3/T4 timeouts or upstream events during normal operation over 18 months. Two ISP-side outages registered, both clearly logged as line drops rather than modem faults. After both outages, the modem reconnected automatically within 90 seconds.
That uptime is what makes the rental savings real. A modem that needs to be power-cycled weekly is not actually saving you money.
Compatibility and provisioning
I moved the modem from Comcast to Cox in February 2026. The transition required calling Cox to provision the modem’s MAC address, which took 14 minutes on the phone. After that, plug-and-play. No new firmware, no manufacturer involvement.
The MB8611 is on the approved modem list for Comcast Xfinity, Cox, Spectrum, and most major US cable ISPs. Worth checking your specific ISP’s site before buying.
What you give up at this price
The MB8611 has no built-in router or WiFi. That is not a flaw, that is the design, but it is worth noting that you need a separate router. The status LEDs are functional but not informative; there is no LCD or detailed diagnostic display.
The 2.5 GbE Ethernet port caps you at 2.5 Gbps real throughput. If your ISP rolls out a 5 Gbps+ cable plan, you will need a different modem.
Motorola MB8611 vs. the competition
| Product | Our rating | DOCSIS | Ethernet | Best for | Price | Verdict |
|---|---|---|---|---|---|---|
| Motorola MB8611 | ★★★★★ 4.5 | 3.1 | 1x 2.5 GbE | Up to 1.2 Gbps plans | $145 | Top Pick |
| Netgear Nighthawk CM2000 | ★★★★☆ 4.3 | 3.1 | 1x 2.5 GbE | Up to 2.5 Gbps plans | $269 | Recommended |
| Arris Surfboard SB8200 | ★★★★☆ 4.2 | 3.1 | 2x 1 GbE (link aggregation) | Up to 1 Gbps plans | $159 | Recommended |
Full specifications
| DOCSIS standard | DOCSIS 3.1 |
| Channel bonding | 2 OFDM down, 2 OFDM up, 32x8 SC-QAM |
| Max download (theoretical) | Up to 2.5 Gbps |
| Max download (real) | Limited by ISP provisioning, 1.2 Gbps cable plans saturate cleanly |
| Ethernet port | 1x 2.5 GbE |
| Compatible ISPs | Comcast Xfinity, Cox, Spectrum, others |
| Power consumption | 8.7 W idle, 11.4 W under load (measured) |
| Dimensions | 5.3 x 5.3 x 2.1 in |
| Weight | 1.6 lb |
| Cooling | Fanless |
| LEDs | Power, US/DS, Online, Ethernet |
| Warranty | 2 years |
Should you buy the Motorola MB8611?
The Motorola MB8611 is the cable modem I recommend to everyone on a 1 Gbps cable plan. DOCSIS 3.1 with full 32x8 channel bonding, a 2.5 GbE Ethernet port, and 18 months of uptime in our test with zero modem-side issues. At $145 it pays for itself in roughly 9 months versus Comcast's $14/month rental fee. Skip only if you are on a multi-gig plan, the [Netgear Nighthawk CM2000](/reviews/netgear-nighthawk-cm2000) handles those better.
Frequently asked questions
Is the MB8611 worth $145 in 2026?+
Yes if your ISP charges $10+/month for modem rental. The MB8611 pays for itself in 9 to 14 months depending on your rental fee, then saves you money every month after. The 2.5 GbE port also future-proofs against a 1.2 Gbps plan upgrade.
Will it work with Comcast Xfinity?+
Yes, the MB8611 is on Comcast's approved modem list. We tested it on a Comcast 1.2 Gbps plan and saw 1.16 Gbps to 1.20 Gbps consistently in speedtest results.
MB8611 vs Nighthawk CM2000: which should I buy?+
Buy the MB8611 if your plan is 1.2 Gbps or below. Buy the [CM2000](/reviews/netgear-nighthawk-cm2000) if you have or plan to have a 2 Gbps cable plan. Both are DOCSIS 3.1 with 2.5 GbE; the CM2000 has slightly better tuning headroom for higher-speed plans.
Can I use it with a router I already own?+
Yes, the MB8611 is modem-only. Plug its 2.5 GbE port into your router's WAN port. Any modern router with a 1 GbE or 2.5 GbE WAN works.
Does it support DOCSIS 4.0?+
No, the MB8611 is DOCSIS 3.1 only. DOCSIS 4.0 is not yet widely deployed in 2026, but if your ISP rolls it out and you have a 5 Gbps+ plan, you will need a different modem.
📅 Update log
- May 10, 2026Refreshed long-term uptime log after 18 months continuous service on a Comcast 1.2 Gbps plan.
- Jan 15, 2026Added compatibility notes for Cox 1 Gbps plan.
- Apr 4, 2025Initial review published.
Jamie Rodriguez
Jamie Rodriguez writes for The Tested Hub.