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

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?

6 REPLIES 6
Lead Moderator

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

Good morning. 

 

No we do not throttle throughput when you are using your own router connected to our D3.1 modem.

 

Some information that would help to diagnose the issue can be found here: 

DATA-TO-POST-TO-GET-HELP-FROM-THE-COMMUNITY 

 

Regards,

Julia

Social Media Customer Service-Lead Moderator

 

Helper

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

Is any other device connected to the router when you are having these issues? Does the router have QoS or other data management system activated? 

Sharer

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

Just spitballimg... but double check your router's NAT acceleration options. May need to make sure Cut Through Forwarding (CTF) or something is enabled.

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

I want to reiterate that the routers tested here are all flagship routers—Netgear Nighthawk R7000, Asus AX88U, and Asus GT-AX11000—and all should be able to sustain higher than ~400 Mbps download speed during a speed test. The Asus models are Wi-Fi 6 units, capable of multi-gig throughput when wireless or wired. Each device is run a clean, controlled state, with no other LAN ports/devices in use.

 

All routers are running up-to-date firmware, exhibit no hardware defect (monitored via individual core CPU usage in the GUI), are connected via CAT7 ethernet, and have all elective software/bandwidth regulation functions (including QoS) firmly disabled.

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

Hi there,

 

Both of the Asus Wi-Fi 6 units in use here (Asus AX88U and Asus GT-AX11000) are quad-core, hardware-intensive models with more than enough resources to handle single-gig WAN-to-LAN throughput.

 

Both NAT Acceleration and CTF are enabled by default and hidden in the GUI.

Sharer

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

Hmmm... curious indeed. NAT acceleration/QoS are usual suspects after cables/link speed negotiation.

Perhaps a reset of the windows stack? Can try the TCP Optimizer over at speedguide.net to reset everything to winblows defaults with just a few mouse clicks (rightclick, run as admin so it can run the netsh commands properly and all)--will call for a reboot and will recheck for chimney and all that good stuff again.

Worth a shot?