Bufferbloat is the lag you get when your connection is busy. When someone in your home starts a big download, upload or stream, your router fills its buffers with data, and your game packets wait in the queue. Ping that's normally 20 ms can jump to 200 ms or more. The good news: bufferbloat is one of the easiest lag problems to fix, usually with a single router setting called SQM.
How bufferbloat happens
Every router and modem has buffers: small memory queues that hold packets when data arrives faster than it can be sent. Some buffering is necessary. The problem is that many devices have oversized buffers. Under load, they queue hundreds of milliseconds of data instead of dropping a few packets to signal "slow down".
Your game sends small, time-sensitive packets. They end up stuck behind huge queues of download or upload data.
Signs you have bufferbloat
- Your ping is fine when you're alone and bad when others are online.
- Lag appears the moment someone starts a video call or a game download.
- Speed tests show great Mbps, but games feel laggy.
- Uploads hurt even more than downloads: cloud backups, streams, sending large files.
How to test for bufferbloat
Run a test that measures latency under load:
- Waveform bufferbloat test — gives a grade from A+ to F and shows latency during the download and upload phases.
- Cloudflare speed test — shows "loaded latency" for download and upload.
How to read the results:
| Latency increase under load | Verdict |
|---|---|
| under 5 ms | Excellent |
| 5–30 ms | OK for most games |
| 30–100 ms | Noticeable in competitive games |
| 100+ ms | Severe — fix it |
How to fix bufferbloat
1. Enable SQM on your router
Smart Queue Management (SQM) keeps queues short and shares the connection fairly between traffic types. Look for:
- OpenWrt: SQM with CAKE or fq_codel
- Ubiquiti: Smart Queues
- Other routers: features called Smart Queue, bandwidth management or QoS with bandwidth limits. Check whether yours is real SQM or just a priority list.
2. Set the bandwidth limits correctly
SQM only works if the router is the bottleneck, not your ISP's modem. Set the download and upload limits to about 90–95% of your measured speed. Test again and lower the limits slightly if latency still rises.
3. If your router has no SQM
- Use QoS to prioritise your gaming device, together with a bandwidth limit slightly below your line speed.
- Or upgrade to a router with real SQM. For many households this is the single best gaming upgrade.
4. Reduce the load
As a stopgap, schedule large downloads and backups for times when nobody is gaming.
Does bufferbloat affect ping on Ethernet?
Yes. Bufferbloat happens in the router and modem, not in the cable. A wired PC suffers just as much when someone else is uploading. That's why Ethernet alone doesn't always fix lag.
