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What is Bufferbloat?

Bufferbloat is lag that appears only when your connection is busy — pages, calls and games stall the moment a download or upload starts.

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Bufferbloat is extra delay that shows up only under load. When you start a big download, a cloud backup or a video upload, oversized buffers in your router or modem fill up with data. Every other packet — a game input, a Zoom voice frame, a web request — has to wait in that queue, so latency jumps from ~20 ms at rest to hundreds or thousands of ms.

Think of a single-lane road: at rest, cars flow freely. Add one slow truck (a big download) and everything behind it crawls, even a fast motorbike (your ping). The road's speed limit didn't change — the queue did.

This is why your internet can show a great speed-test number yet still feel laggy during calls or gaming: the Mbps is fine, but the delay-under-load (bufferbloat) is the real problem.

What this measures

  • Idle (resting) latency vs latency while the link is fully loaded
  • The size of the latency spike in each direction — download and upload separately
  • Whether the spike is in your router/modem queue or on the ISP link

How it works

  1. Run the bufferbloat test on the connection that feels bad
  2. Read your bufferbloat against the good-vs-bad table below
  3. Apply the fixes in order and re-test to confirm the improvement

Why this matters

Bufferbloat is the #1 hidden cause of 'fast internet that still lags'. It wrecks video calls, cloud gaming and competitive gaming exactly when another device is downloading — very common on shared Indian home broadband and mobile hotspots.

Top fixes

  • Enable SQM / Smart Queue Management (cake or fq_codel) on your router — the single most effective fix
  • Replace an old ISP-provided modem/router with one that supports SQM (OpenWrt, some ASUS/Netgear models)
  • Set the SQM bandwidth cap to ~90% of your plan so the queue can never fully fill
  • On mobile hotspots, avoid running large uploads while on a call — hotspots buffer heavily
  • Shift heavy downloads to off-peak hours on shared home broadband

FAQs

Is bufferbloat the same as slow internet?

No. Slow internet is low Mbps; bufferbloat is high delay under load. Your speed can be high while bufferbloat still makes calls and games lag — they are measured differently.

How do I test for bufferbloat?

Run our bufferbloat test: it measures your latency at rest, then again while saturating the link, and reports the increase as an A-to-F grade. A big jump means bufferbloat.

Can my ISP fix bufferbloat?

Usually you fix it yourself with SQM on your router. The oversized buffers are typically in your home equipment, so a good SQM setup keeps the queue short regardless of the ISP.

Test my bufferbloat →

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