Just a quick note to relate a problem I recently encountered, that might interest others.
Hardware Configuration: Arris cable Modem connected to a Netgear /ac router, using a gigabit Ethernet link.
About six months ago I was experimenting with the Netgear router, and enabled both its Downlink and Uplink QoS High Performance options. The performance did increase slightly, but nothing special. Since there seemed to be no problems, I left them enabled and proceeded to forget about having changed them.
Then about two months ago, problems slowly started showing up. First a gaming PC attached directly through a Cat-6 cable to the Router started dropping in speed, from over 200 Mbps, to 100 Mbps, then to less than 10 Mbps. A wireless PC at the other end of the house, dropped from 17+ Mbps to an erratic 3 Mbps. Finally, the Up-link speeds on both PC's, which had been rock- solid at over 10 Mbps, dropped to less than 0.4. Netflix was also taking a very long time to start up
I tried all the simple things, like checking cables, VPN enabled and disabled, rebooting everything, but nothing helped.
Finally, after removing the router from the setup, and connecting the gaming system system directly to the cable modem, it's performance was back to over 200 Mbps. Then, returning the cables to the original connections, caused the entire network to crawl again. Obviously the router was the weak link.
On a hunch, I disabled both the Up-link and Down-link QoS options in the Netgear router, and rebooted everything.
Voila. All the problems were fixed.
Apparently, the QoS settings at my ISP had changed from their original values, and were no longer compatible with the Netgear router QoS parameters. Note that downloading the latest Router F/W also had no effect.
Disabling QoS was the solution to my problems.
Sometimes the best thing to do is just leave well enough alone.
Update to my previous QoS Post:
It looks like Netgear has been having issues with QoS, for at least 2 years. If you search their KB articles, you'll find several articles on resolving QoS issues.
However, all of them conclude that you'll probably be better off by disabling both the Up-stream AND Downstream options - which are disabled by default.
It appears that the most reliable way to improve performance is to pay your ISP for faster service. The same thing goes for slow VPN service.