ARRIS S33 vs S34 vs Motorola MB8611 Cable Modem Comparison
Buy the ARRIS SURFboard S34 over the older ARRIS S33 and Motorola MB8611 if you use Comcast Xfinity, because only the S34 is certified for Xfinity Next Gen Mid-Split networks delivering 100 to 250+ Mbps upload speeds over 85 MHz OFDMA upstream channels. On Cox and Spectrum legacy splits, the S33 and MB8611 deliver identical multi-gigabit downloads via their 2.5GbE ports.
- Xfinity Next Gen Upload Winner: Only the ARRIS SURFboard S34 is certified by Comcast Xfinity for Mid-Split (5–85 MHz) upload speeds up to 250+ Mbps; the S33 and MB8611 are permanently throttled to 35–40 Mbps upload on Xfinity.
- Ethernet Port Warning: The ARRIS S34 and Motorola MB8611 have a single
2.5GbEport; the ARRIS S33 has1x 2.5GbE + 1x 1GbE(do not plug two devices into the S33 unless your ISP gives you two public IPs!). - Zero Puma 6/7 Chipset Flaws: All three modems use low-latency Broadcom BCM3390 DOCSIS 3.1 silicon with Active Queue Management (DOCSIS-PIE).
- Stop Paying $15/mo Rental Fees: Buying a standalone modem pays for itself in 10–14 months and eliminates ISP gateway Double NAT and forced public hotspots.
Why the ARRIS S34 Unlocks 200+ Mbps Uploads on Comcast Xfinity (Mid-Split)
For the past two decades, North American cable networks (Comcast Xfinity, Cox, and Charter Spectrum) operated on a legacy Sub-Split RF spectrum allocation, dedicating only a tiny 5 MHz to 42 MHz slice of coaxial spectrum to upstream traffic while reserving 54 MHz to 1,002 MHz for downstream downloads. That narrow 42 MHz ceiling is why even a 1,200 Mbps cable plan historically crawled along at a painful 35 Mbps upload speed.
Comcast Xfinity has now upgraded the majority of its US footprint to Next Gen Speed Tier (Mid-Split DOCSIS 3.1), shifting the upstream diplexer boundary from 42 MHz up to 85 MHz and activating wide OFDMA upstream channels that boost residential uploads from 35 Mbps to 100–250+ Mbps. Even though the older ARRIS S33 and Motorola MB8611 technically contain 85 MHz hardware diplexers, Comcast never certified their bootfiles for Next Gen tiers. The ARRIS SURFboard S34 is specifically engineered and officially certified on Xfinity's Next Gen Device List—meaning switching from an S33 or MB8611 to an S34 on Xfinity immediately multiplies your upload speed by 5x.
Hardware Architecture: Broadcom BCM3390, 2.5GbE Ports & Thermal Design
All three modems—the ARRIS SURFboard S33, ARRIS SURFboard S34, and Motorola MB8611—are pure standalone DOCSIS 3.1 cable modems (no built-in Wi-Fi router) built around the gold-standard Broadcom BCM3390 processor. None of them suffer from the infamous Intel Puma 6/7 hardware latency jitter bug, and all three support 32x8 DOCSIS 3.0 SC-QAM fallback channels alongside 2x2 DOCSIS 3.1 OFDM/OFDMA channels plus built-in DOCSIS-PIE Active Queue Management (AQM) to reduce upstream bufferbloat.
Pay close attention to the rear Ethernet port layout:
- ARRIS S34 & Motorola MB8611 (1x 2.5GbE Port): Feature a single 2.5GBASE-T port designed to plug straight into your router's 2.5GbE WAN port. The Motorola MB8611 also includes a wider vented vertical case and dedicated front status LEDs for downstream/upstream bonding.
- ARRIS S33 (1x 2.5GbE + 1x 1GbE Ports): Includes a second 1GbE port, which frequently confuses buyers. Because a standalone modem does not have a DHCP server or NAT router, you cannot plug both a router and a PC into the S33 unless you pay your ISP for two separate public IPv4 leases; the first device to boot will grab your single ISP IP and leave the second device offline.
ISP Compatibility Matrix: Xfinity, Cox & Spectrum Policies
Before buying your own DOCSIS 3.1 modem, check how your specific cable provider handles customer-owned equipment in 2026:
- Comcast Xfinity: Allows customer-owned modems on all tiers up to the 2,000 Mbps (Gigabit x2) plan. Buy the ARRIS S34 (or Netgear CM3000 / Hitron CODA56) to get full 100–250+ Mbps Next Gen Mid-Split uploads and save the $15/month xFi Gateway rental fee ($180/year). Note: if you do not live in an unlimited-data region, verify whether Xfinity charges more for Unlimited Data on customer-owned modems vs xFi Complete in your state.
- Cox Communications: Certifies the ARRIS S33, S34, and Motorola MB8611 across plans up to 2 Gbps, saving $14/month over the Panoramic Wifi gateway.
- Charter Spectrum: Spectrum already provides a free standalone DOCSIS 3.1 2.5GbE modem (such as the EU2251/ET2251) at $0/month; furthermore, Spectrum is rolling out High-Split (5–204 MHz) symmetrical gigabit exclusively on Spectrum-issued modems first, so Spectrum subscribers should usually keep the free Spectrum standalone modem and pair it with their own router.
How to Check Coax Signal Levels (dBmV & SNR) at 192.168.100.1
Once you activate your ARRIS or Motorola modem via the Xfinity or Cox mobile app, log into the modem's local diagnostic page at https://192.168.100.1 (on ARRIS S33/S34, default username is admin and the password is the last 8 digits of the serial number printed on the bottom label; on Motorola MB8611, default is admin / motorola).
Inspect your coaxial line health against these DOCSIS 3.1 engineering thresholds:
- Downstream Power Level: Must sit between
-7.0 dBmVand+7.0 dBmV(0.0 dBmVis ideal;-10to+10 dBmVis the outer specification limit). - Downstream SNR / MER: Must be
>35.0 dBacross all 256-QAM channels and the OFDM PLC channel (38–42 dBis ideal). - Upstream Transmit Power: Must sit between
+35.0 dBmVand+49.0 dBmV. If Upstream Power exceeds+51 dBmV, remove unnecessary coaxial splitters between the street drop and your modem so the amplifier doesn't drop offline during temperature swings.
ARRIS S34 vs ARRIS S33 vs Motorola MB8611 Technical Comparison
| Feature / Specification | ARRIS SURFboard S34 | ARRIS SURFboard S33 | Motorola MB8611 |
|---|---|---|---|
| DOCSIS Chipset | Broadcom BCM3390 (32x8 + 2x2 OFDM) | Broadcom BCM3390 (32x8 + 2x2 OFDM) | Broadcom BCM3390 (32x8 + 2x2 OFDM) |
| Xfinity Next Gen Upload Certified? | Yes (100–300 Mbps Mid-Split Upload) | No (Capped at 35–40 Mbps Upload) | No (Capped at 35–40 Mbps Upload) |
| Upstream Frequency Switch Range | Switchable 5–42 MHz or 5–85 MHz | 5–42 MHz (Not certified for Xfinity 85 MHz) | 5–42 MHz (Bootfile issues on Xfinity) |
| Ethernet Ports | 1x 2.5GbE RJ45 Port | 1x 2.5GbE + 1x 1GbE RJ45 Ports | 1x 2.5GbE RJ45 Port |
| Surge Protection & Chassis | Compact White/Black Dome | Compact White Dome | Large Vertical Vented + Coax Lightning Surge |
| Best Use Case in 2026 | Comcast Xfinity & Cox (Up to 2.5 Gbps) | Cox & Legacy Sub-Split Cable Only | Cox Only (Avoid on Xfinity due to rdkb reboots) |
Cable Modem Upgrade, Activation & Coax Signal Checklist
- Choose the ARRIS SURFboard S34 if you use Comcast Xfinity so your account automatically provisions for 100–250+ Mbps Next Gen upload speeds.
- Take a photo of the HFC MAC Address and Serial Number on the bottom of the modem before sliding it into your networking rack.
- Connect the modem directly to the main incoming coaxial line (or the first 5–1002/1218 MHz MoCA-rated two-way splitter) without amplified splitters on the modem leg.
- Plug only your router's WAN port into the modem's 2.5GbE port; whenever swapping routers, power-cycle the cable modem for 30 seconds to clear its learned CPE MAC lock.
- Activate the modem using the Xfinity or Cox mobile app, then wait 10 minutes for the modem to download its ISP configuration bootfile and reboot twice.
- Log into https://192.168.100.1 to confirm Downstream Power is between -7 and +7 dBmV, SNR is >36 dB, and Uncorrectable Codewords are not climbing rapidly.
Frequently Asked Questions
Why does the Motorola MB8611 have random reboot complaints on Comcast Xfinity?
Over the past two years, Comcast pushed updated DOCSIS 3.1 firmware profiles across parts of its network that caused customer-owned Motorola MB8611 modems to experience T3/T4 timeout reboots and locked them out of Mid-Split upload tiers. For Xfinity, the ARRIS SURFboard S34 (or Hitron CODA56) is far more reliable and officially Next Gen certified.
Why did my internet stop working when I unplugged my old router from my ARRIS modem and plugged in a new router?
Standalone cable modems lock onto the MAC address of the very first Ethernet device plugged into them after boot. Whenever you connect a different router or laptop to a cable modem, unplug the modem's power cord for 30 seconds and plug it back in so it clears its CPE MAC table and issues a public IP to the new router.
Can I access 192.168.100.1 through my router without unplugging Ethernet cables?
Yes! As long as your home router's LAN subnet is not also set to 192.168.100.0/24, your router will automatically route requests for https://192.168.100.1 out the WAN port to the cable modem's management interface.
What do the front LED colors on the ARRIS S33 and S34 mean?
A solid Blue LED means the modem is actively bonded on high-speed DOCSIS 3.1 OFDM channels. A solid Green LED means the modem is connected in legacy DOCSIS 3.0 mode only, and flashing Green/Amber indicates the modem is scanning coaxial frequencies or registering with the ISP CMTS.