SQM does not work - what is wrong here?

Router
1

Subject: SQM enabled with values set, but no actual traffic shaping occurring (GL-MT6000, firmware v4.9.0)

Device: GL-MT6000 (Flint 2)
Firmware: v4.9.0

I'm trying to fix bufferbloat on a 1 Gbps AT&T Fiber connection using SQM. Setup:

  • WAN is confirmed getting a real public IP (not double-NAT) — verified via AT&T gateway IP Passthrough correctly assigned to the Flint 2's MAC address.

  • FLOW CONTROL → SQM is toggled on.

  • Download set to 717 Mbps, Upload set to 787 Mbps (roughly 85% of my measured 840/920 Mbps real speeds).

  • Tried Queue Rule as both cake and fq_codel.

  • Rebooted the router after every settings change.

Problem: Running a bufferbloat test (waveform.com/tools/bufferbloat) consistently shows actual throughput exceeding my configured caps — e.g., download hitting 840-860 Mbps and upload hitting 900-940 Mbps during the test, well above the 717/787 limits I set. This indicates no shaping is actually being applied, despite SQM showing as enabled with the correct values saved. Bufferbloat grade stays at a C with +80-95ms upload latency under load regardless of which queue discipline is selected.

Has anyone else seen SQM silently fail to shape traffic on this model/firmware version? Is there a known fix, or should I try a factory reset and reconfigure from scratch? Happy to provide logs if that helps diagnose.

2

I have always set up SQM via Luci (advanced settings) and luci-app-sqm package, there are more controls, I did find that by default 4.9.* seems to point SQM at the Lan–Bridge and not the LAN port used for wan, changing this (to eth1) in Luci had the desired effect and applied the SQM setting correctly as on the Bridge it seems to have no to little effect.

Maybe you are seeing the same too. (NB. turn on SQM in LUCI turns it on in the GL-Gui, but use Luci to set values and protocols.)

3

Network Acceleration is off???