Ping Argus › What is bufferbloat, and how do you fix it?

What is bufferbloat, and how do you fix it?

Bufferbloat is latency that collapses the instant your connection gets busy. It is the single most under-reported fault on home internet, it has nothing to do with how fast your line is, and on most routers it is a settings change rather than a purchase.

Last updated 29 August 2026

What is actually happening

When traffic arrives faster than a link can send it, something has to hold the excess. Routers hold it in a queue. The problem is that manufacturers made those queues enormous, on the reasoning that dropping packets is bad and buffering them is polite.

It is not polite. TCP needs to see a dropped packet — that is how it learns to slow down. Give it a huge buffer instead and it keeps accelerating, filling the queue until every packet behind it waits half a second to get out. Your download still finishes at full speed. Everything else on the connection is now standing in that queue.

That is why a call breaks up the moment somebody starts a download, and why it is not fixed by paying for a faster line: a bigger pipe just fills a bigger queue.

How to test for it

You cannot see bufferbloat in an ordinary speed test, because an ordinary speed test measures throughput and reports latency separately, when the line is idle. The measurement that matters is latency during the transfer.

Run a test that measures idle latency, then keeps measuring while it saturates the line in both directions. The difference between the two is your bufferbloat. Under 30 ms of rise is good. Over 200 ms is severe, and you will be feeling it daily.

The fix, in order

1. Look for SQM, Smart Queues, QoS, Adaptive QoS or Bandwidth Control in your router's settings. Different manufacturers use different names for the same feature.
2. Set the shaper to about 90% of your real measured speeds, not the speeds on your bill. Slightly under is the entire trick: it keeps the queue on your router, where the algorithm can manage it, instead of at the provider where it cannot.
3. Re-run the test. Latency under load should drop dramatically, and you will notice it on calls immediately.
4. No such setting anywhere? That is the single best reason to replace a router. Anything running OpenWrt handles it properly, as do most GL.iNet, eero and Ubiquiti devices. Ask your manufacturer for a firmware update first — some have added it.

Why 90% and not 100%

The queue forms wherever the bottleneck is. If your router shapes at exactly your line speed, the bottleneck stays at the provider's equipment, in a buffer you have no control over. Shaping slightly below moves the bottleneck to your own router, where a modern queue algorithm can drop or mark packets intelligently.

You are trading a few per cent of peak throughput for a connection that stays usable while it is busy. On any line above about 50 Mbps that is a trade worth making without thinking about it.

How bad is yours?

This site measures it directly: idle latency first, then latency while downloading and uploading at full tilt, reported as the rise. It also tells you the shaper numbers to type in, calculated from your own measured speeds.