Good catch; I added that to my note. I've never had traffic meter on.
Do you have the same nighthawk X8 (R8500) or some other router? If you have the same as me, it would be interesting to compare settings and figure out why you can get the full throughput while I cannot. That investigation may help others.
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Full disclosure that I am a Comcast employee but not posting in any sort of official capacity. My goal here is to share some troubleshooting I did to improve my speed tests in the hopes it may help others.
I recently installed Gigabit to give it a try. Installation was mainly a matter of switching out my current modem for an XB6. The technician also performed quite a bit of tests in the house and installed an amplifier since my signal was decent but borderline.
Speed tests after the completed install showed the expected speeds of roughly 950Mb down/40 up. This was with the technician's PC plugged directly into an XB6 port. I could get similar speeds with a direct PC connection to the XB6. This tells me that my PC (skylake i5 class) and embedded ethernet port have the performance needed to take advantage of the Gig speed tier.
However, my production setup connects the PC to an unmanaged gigabit switch (Trendnet TEG-S82g) with that switch connected to a dedicated and arguably high-end wireless router ( Netgear Nighthawk X8 ) with latest firmware. With this connection, I started seeing speed tests of only ~300Mb down and sometimes as low as 90Mb down. The first piece of troubleshooting attacked this issue; the bottom line is that the router had somehow negotiated a link to the XB6 at less than gigabit speed. A simple unplugging and replugging of the XB6<-->router ethernet cord forced a re-negotiation to gigabit speed and I was able to get 400-425Mb download speeds.
At this point I upgraded all cabling to brand-new Cat6 to remove cabling problems from the equation before proceeding. With that cabling and a direct connection to the XB6, I could get back to the 940Mb speed from before, but the normal setup was still giving about 420Mb.
Digging into Netgear forums, I noted that many users said that QoS and traffic meter needed to be turned off for best performance with Gig ISP connections. Mine has always been off, so that was no help. Another suggestion was to turn off MAC filtering (aka Access control), which I use heavily. Turning off this option got me to about 537Mb down. Removing the unmanaged switch from the equation and connecting the PC directly to the router showed effectively no change in speed.
For the last trick, I turned on 802.3ad link aggregation on the router and the PC and connected two cables from the PC to the router's aggregation ports (without the unmanaged switch in the picture). WIth this setup, speeds increased to 630Mb.
I'm still disappointed that I can't get to true Gig speed with full hard-wired connections, even with link aggregation. But the issue seems to be either with the capability of the Nighthawk (a sad statement given its near-flagship status) or possibly with the XB6 and how it communicates with the router. I find the latter hard to believe.
Edited to update: I've finally been able to get Gig speed on this Nighthawk, and even on a single link without aggregation. The additional feature I had to turn off was "block sites". Ultimately it seems that the router simply does not have the horsepower to provide full Gig bandwidth if _any_ packet or other inspection features are used. This includes QoS, access control, block sites, block services, etc.
Bottom line: if you cannot get true Gig speed in speed tests when subscribed to the Gig speed tier, make sure it is not your PC, router, and/or cabling at fault.
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