RT-AC86U wired WAN-LAN throughput with/without QoS (stock fw)

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New Around Here
Recently upgraded my ISP service to 300 Mbps down / 10 Mbps up. Running a web-based speed test from my ISP's server (WAN side) on a desktop PC wired to LAN port of my Asus RT-AC86U I typically reach 20% above provisioned ISP speeds with QoS off, but as soon as I enable any QoS features on the RT-AC86U, my download and upload speed test results drop significantly by roughly 50% to between 60 and 120 Mbps down / 6 to 9 Mbps up. The result are on the upper end (still much lower than no QoS) if the desktop PC I'm testing on is placed in the highest priority, and lower end for other QoS configs, and tests are being done late at night with everything idle. I've mostly wanted to use the "Traditional QoS" (priority profiles) but also tried the "Adaptive QoS" (application profiles), and I found similar throughput drop with both types of QoS. Is much lower throughput when using QoS features typical for this RT-AC86U model, or should I be able to reach full performance by further tweaking the traditional QoS settings or by avoiding for some QoS feature bottleneck? I recall that reviewer testing for this device showed WAN-LAN throughput up to 800 Mbps even with multiple features turned on, which was of course years ago and different firmware.

I'm running current stock firmware version I have up to 20 devices connected (split wired/wireless), typical dual-band wifi config with one guest WiFi. I do use Firewall (enabled) with some "Network Services Filters" blacklisting about 10 outgoing ports (SMB/NetBios/SMPT/SNMP, etc), and parent controls are enabled using device blocking schedule and "Web & Apps Filters" on a small subset of devices. The following features are disabled (where possible) or not used: USB ports and storage, AiProtection (no Network Protection, Malicious sites, two-way IPS, or Infected device blocking), AiMesh, AiCloud, IPv6, and VPN features (all disabled).


Senior Member
I've got an AC86U and used Adaptive QoS for a bit last year with our 200/20 service and it behaved as expected, i.e. up and down speeds matched the percentage of the max I entered into the relevant QoS fields.


Part of the Furniture
Does anyone have an RT-AC86U anymore?

Yep. I would install the latest firmware, reset the firmware, configure it from scratch per my install notes, and speedtest with a wired PC starting at the ISP modem. That should easily measure your provisioned ISP speeds. If not, try different Gigabit Ethernet cables.

Then build up your network how you want it, one step at a time, while keeping an eye on performance.


John Davis

Regular Contributor
what QoS settings did you try - adaptiive and 'automatic' bandwidth setting? Try changing to manual bandwidth setting and putting in what your link speeds actually are - I found on automatic it would regularly give low speeds like you're seeing (presumably because it was under-estimating my connection speed), with it explicitly set that went away

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