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Test and Fix Bufferbloat on Your Home Connection

High ping under load is bufferbloat, not a slow line. Measure it idle and loaded, then enable Smart Queue on the router and check the grade again.

by@guidox updated:10/30/26 time:20 min level:Intermediate tested on:Windows 11 24H2, 500 Mbit/s fibre works on:Windows 10, Windows 11, any router with QoS/SQM
TL;DR

Run the **Waveform bufferbloat test** once idle and once while the line is loaded. If latency climbs by more than about **30 ms**, enable **SQM / Smart Queue** on the router at **90% of your measured speeds**.

Before you start

Requirements

  • A PC connected by Ethernet
  • Access to the router's admin page
  • Nothing else downloading during the test
Step by step

Instructions

01

Measure the idle baseline

Run the bufferbloat test with the line quiet and keep the result: idle latency and the letter grade.

https://www.waveform.com/tools/bufferbloat
tipRun it twice. The first run compiles nothing and always looks better than the second.
02

Read what the grade means

A or B is fine. C and worse usually means the router queues packets in a deep buffer, and the damage shows up on **upload** first - which is why a video call can ruin a game.

03

Test on cable, not Wi-Fi

Wi-Fi adds its own retries and hides the router's queueing. Plug the test machine into a LAN port before drawing conclusions.

04

Enable Smart Queue in the router

Look for **QoS**, **SQM**, **Smart Queue** or **Cake/fq_codel** in the router UI. Set the download and upload limits to roughly 90% of the speed you measured - a queue only works when it is slightly shorter than the line.

Download: 90% of measured speed
Upload: 90% of measured speed
Queue type: cake / fq_codel
⚠ warningAbove 100% the queue never engages and the grade stays bad.
05

Re-run the test

The loaded latency should sit close to the idle one, and the grade should move to A or B. Run both tests again at the time of day you actually play.

06

If the router has no SQM

Stock firmware without QoS cannot fix bufferbloat. Options are a router with SQM support, OpenWrt on a supported model, or a small x86 box doing the routing. Software 'game boosters' on the PC do not touch the queue.

Troubleshooting

Common issues

Speeds dropped after enabling SQM

Expected - the shaper is doing its job. Raise both limits to 95% if the grade stays good, or lower them again if it does not.

Only upload looks bad

Upload queues fill first on home connections. Set the upload shaper 5% lower than the measured value and retest.

Latency is fine but the game still lags

That is packet loss or a distant server, not bufferbloat. Check the in-game latency graph and the server region.

The test always reports A but games stutter

A VPN or the ISP's own queue can add jitter the test does not see. Test with the VPN off and compare the in-game ping graph.

FAQ

Frequently asked

Is bufferbloat my ISP's fault?

Usually it is the router's queue, sometimes the ISP's. Fixing the local queue is cheap and gets most of the benefit.

Does it increase my bandwidth?

No, it slightly reduces it. You trade a few percent of speed for stable latency.

How to undo this

Turn SQM/QoS off in the router and save. The line returns to its old behaviour, including the bad latency under load.

Changelog · 1 entry
  1. 2026-10-30
    First version
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