Test for Bufferbloat

What Bufferbloat Is and Why It Matters

Bufferbloat is a specific type of latency problem that has nothing to do with your internet plan speed. It happens when a download or upload saturates your connection and the router or modem's buffers fill up — temporarily holding packets for hundreds or even thousands of milliseconds before forwarding them. During that window, a video call stalls, a game spike-lags, or a voice call chops up, even though your speed test a minute later shows your full advertised speed.

The frustrating part about bufferbloat is that it is invisible to standard speed tests, which measure peak throughput under ideal conditions. A connection with severe bufferbloat can report 500 Mbps download while simultaneously making calls unlivable whenever someone else in the house starts a large download. The fix is not faster internet — it is Active Queue Management (AQM) on the router. But first, you need to confirm it is actually bufferbloat causing your problem.

How to Test for Bufferbloat

The best free tool is the Waveform Bufferbloat Test at waveform.com/tools/bufferbloat. It runs a download and upload load test while simultaneously measuring ping latency — the key is that it measures latency while the line is loaded, not during idle conditions. Standard speed tests measure idle latency, which tells you nothing about how the connection behaves when it is actually carrying traffic.

The Waveform test grades your connection A through F based on latency increase under load:

Run the test on a wired Ethernet connection first. If you score C or below, you have bufferbloat. If you score A on Ethernet but C on Wi-Fi, the problem is the Wi-Fi radio's own buffers, not your modem or ISP.

Confirming the Problem Yourself

You can verify bufferbloat without a web tool using just a terminal. Start a continuous ping to 1.1.1.1 (ping 1.1.1.1), then simultaneously start a large download — a Linux ISO, a game update, anything that saturates your connection for several minutes. Watch what happens to your ping times during the download. If idle ping was 15ms and it jumps to 400ms while downloading, that is bufferbloat. If it stays near 15ms throughout, your router is managing queues well.

Fixing Bufferbloat: Active Queue Management

The root cause is oversized hardware buffers in your modem or router that allow too many packets to queue before discarding them. The solution is Active Queue Management (AQM) — specifically algorithms like CAKE (Common Applications Kept Enhanced) or FQ-CoDel (Fair Queuing with Controlled Delay), which actively limit queue depth to keep latency under control even during saturation.

• If your router runs OpenWrt or DD-WRT: enable SQM (Smart Queue Management) with CAKE as the algorithm. Set the download and upload limits to 95% of your measured line speed. This is the gold-standard fix and typically brings a grade F connection to A+ without changing anything else.
• If your router has a QoS or traffic management feature: enable it and configure your maximum upload and download speeds. Consumer QoS implementations vary in quality, but most improve bufferbloat substantially.
• If your ISP provides a combo modem/router gateway: you often cannot install AQM firmware. Consider putting the gateway in bridge/IP passthrough mode and adding a router with proper AQM support (Eero, Asus with OpenWrt, or a dedicated OpenWrt device).
• For DOCSIS 3.1 cable modems: some modern gateways (Arris, Motorola with DOCSIS 3.1 OFDM) implement AQM internally. If your gateway's firmware supports it, enabling Low Latency DOCSIS (LLD) can significantly reduce bufferbloat without any router changes.

Frequently Asked Questions

My speed test is great but video calls are terrible. Could this be bufferbloat?

Very likely. Speed tests measure bandwidth under ideal conditions — they do not load the connection with competing traffic at the same time as measuring latency. Bufferbloat only appears under load. If your video calls degrade specifically when someone else in the household is downloading or streaming, bufferbloat is the most probable cause. Run the Waveform test during a time when the problem is happening and look at the latency-under-load reading.

Will getting faster internet fix bufferbloat?

Not necessarily. Faster internet increases how long it takes to saturate the connection, so a 1 Gbps plan shows less bufferbloat than a 25 Mbps plan in everyday use — but when the line does saturate, the latency spike is just as bad. Adding more bandwidth does not fix the underlying queue management problem; it just means saturation happens less often. The correct fix is AQM, not a faster plan.

Is bufferbloat my ISP's fault?

Usually not in the traditional sense. The large buffers that cause bufferbloat are typically in the equipment on your side of the connection — your router or ISP-provided gateway. Your ISP cannot control how your equipment manages its queues. That said, some ISPs use oversized buffers in their head-end equipment that affect your upstream path, particularly on cable DOCSIS connections. If enabling AQM on your router fixes the download latency but not the upload latency, the bufferbloat may be in your ISP's equipment upstream.

How do I know if my router supports CAKE or FQ-CoDel?

Check whether your router can run OpenWrt firmware — the OpenWrt hardware compatibility table at openwrt.org lists supported devices. If your router is on the list and you can flash OpenWrt, CAKE is included in current builds. Alternatively, Eero routers include SQM by default. Asus routers with Asuswrt-Merlin firmware support FQ-CoDel. The Firewalla Gold and Purple run Linux-based firmware with AQM support. For most people, checking whether their current router has any “QoS” or “traffic prioritization” option in the admin UI is the quickest first step — even basic QoS improves bufferbloat compared to no queue management.