Spectrum Internet Gig - Low throughput on download when connected via ethernet through modem - Time Warner Internet

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This question is about "Spectrum Internet Gig - Low throughput on download when connected via ethernet through modem", with Time Warner Cable internet and apps. I recently upgraded from Spectrum's 200/10 tier to the Internet Gig 940/35 tier.

I've been going crazy the last few days, trying to achieve optimal performance when connected via my networking hardware. Namely, I cannot get proper, max throughput for download when a router is active between the Spectrum-provided DOCSIS 3.1 modem and my PC.



Setup is as follows:
• Spectrum DOCSIS 3.1 Internet Gig modem connects to ASUS GT-AX11000 Wi-Fi 6 Router via CAT7 Ethernet Cable

• Desktop PC with Full Duplex 1 Gbps ethernet card connects to Asus GT-AX11000 Wi-Fi 6 router via CAT7 Ethernet Cable



When the above setup is active, I achieve speedtest.net download speeds no higher than 400-410 Mbps, though upload does hit proper ceiling of ~40 Mbps. When the desktop is connected directly to the modem, the download maxes out at far closer to the ideal, clocking in around ~850 Mbps.



I've tried to troubleshoot with multiple routers—all flagship models across two manufacturers—all running current firmware, all factory reset to ensure no software conflict. Multiple ethernet cables tested, as well.



Does anyone have any idea what could be at a fault? More appropriately, anyone on the forum use Internet Gig in tandem with their own router and achieve 1:1 throughput to mirror what the modem directly provides?



From what I've come across on both the r/Spectrum and r/chartercable subreddits, this issue is fairly common when a user is presented with the need to run the Spectrum DOCSIS 3.1 modem alongside user-owned routers. Is there some sort of server-side throttling/throughput limitation in effect when a user does not directly connect to the modem or to a Spectrum-provided router?

Spectrum Internet Gig - Low throughput on download when connected via ethernet through modem?
 
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