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What Is Bufferbloat? (And How to Fix It)

Bufferbloat is lag caused by your router holding too much data in a queue when the connection is busy. Ping that’s 20 ms when idle can jump to 300 ms while someone downloads or uploads, so games lag and calls freeze even on a fast plan. The fix is Smart Queue Management (SQM), often called QoS, on your router.

Updated 4 min read

Why bufferbloat happens

Every router has buffers, small waiting rooms for data. They’re meant to absorb short bursts. But many routers and modems have oversized buffers and no smart way to manage them. When a big download or upload fills the line, the buffer fills up too, and every other packet waits its turn at the back of a long queue.

Your game sends tiny packets that should arrive in 20 ms. Stuck behind megabytes of someone’s Netflix or a photo backup, they can wait hundreds of milliseconds. Bandwidth isn’t the problem; the queue is.

Signs you have bufferbloat

  • Video calls freeze or sound robotic when someone else in the house starts streaming.
  • Games lag only when other people are online, or during uploads.
  • Web pages hang for a few seconds while a large file uploads.
  • Your speed test looks great, but the internet still feels sluggish at busy times.

How to test for bufferbloat

  1. Run the bufferbloat test. It measures ping while idle, then while downloading, then while uploading.
  2. Look at how many milliseconds ping rises under load. Under 30 ms (grade A) is great; over 200 ms (D or F) is a real problem.
  3. Run it two or three times. Upload bufferbloat is usually the worst, because upload is the narrower pipe on most plans.

How to fix bufferbloat

1. Turn on SQM / Smart Queue / QoS

Smart Queue Management uses modern algorithms (fq_codel or CAKE) to keep queues short and give small, time-sensitive packets a fair turn. Names vary by brand:

  • ASUS: Adaptive QoS or “QoS” with fq_codel
  • Netgear Nighthawk: Dynamic QoS (on supported models)
  • TP-Link: QoS (model-dependent)
  • Ubiquiti UniFi: Smart Queues
  • OpenWrt: the luci-app-sqm package with CAKE
  • eero: Optimize for Conferencing and Gaming

Open your router’s settings (the router login finder has the address), turn the feature on, and set the download and upload limits to about 90% of your measured speeds. Giving up a little top speed is what keeps the queue short. Then run the test again.

2. Reduce the load

Schedule cloud backups and game updates for overnight, and limit upload speed in apps like Google Photos, iCloud, OneDrive or Dropbox if they allow it.

3. Replace the router if it has no queue management

Many ISP-supplied routers have no SQM at all. A router that supports Smart Queue or CAKE is the permanent fix. Keep the provider’s box in modem or bridge mode and let the new router handle traffic.

Does a faster plan fix it?

Not reliably. A faster plan just fills the queue faster. It can help if your upload is very small (under 5 Mbps), but queue management on the router is what actually removes bufferbloat.

For other causes of lag, see how to reduce ping, and for the basics of latency read ping and jitter explained.

Frequently asked questions

Is bufferbloat my provider’s fault?
Usually it’s the router or modem in your home, which is where the queue builds up. Sometimes the provider’s modem is the culprit, which is why putting your own SQM-capable router in front of it helps.
Will QoS slow down my internet?
Slightly. Setting SQM to about 90% of your speed trades a little top speed for much lower lag. Most people never notice the lost 10%, but they do notice calls that stop freezing.
What is a good bufferbloat grade?
A or A+ means ping rises by under 30 ms under load, which is excellent. B is fine for most homes. C or worse is worth fixing.