Bufferbloat is when network buffers fill up and hold packets too long. Throughput looks fine. Latency spikes. Calls stutter. Games lag. Anything real time feels broken.

Why Bufferbloat Is Bad

• Queues build during uploads or downloads
• Your packets wait behind big transfers
• Latency can jump from a few milliseconds to hundreds
• Apps time out even though the link is “fast” on paper

How To Measure It With Waveform

The Waveform bufferbloat test runs a baseline latency check (no load), then loads your link with download and upload and measures added latency under load.

How to read it

• Baseline latency: idle round trip time
• Latency under load: what happens during heavy up/down traffic
• Added latency: the difference. This drives the grade
• Grades: A+ through F, with A/A+ meaning very small added latency

My starting point was a B/C range at times. After QoS it moved to A with FQ CoDel and A+ with CAKE. Added latency under load dropped from about 10ms to about 5ms.

What FastTrack Does On MikroTik

FastTrack is MikroTik’s fast path. It bypasses parts of the firewall and the queueing system to boost throughput and lower CPU use. That is great when you want raw speed.

The catch

• If traffic is FastTracked it skips the queue trees
• If it skips queue trees, Smart Queue Management cannot shape it
• Result: bufferbloat persists during heavy transfers

The fix is not to disable FastTrack completely. Keep it for LAN to LAN traffic. Exclude WAN bound traffic so QoS can see and shape it.

Smart Queue Management On MikroTik

I run a MikroTik gateway. Two changes made the biggest difference:

1. Make FastTrack LAN only

• Keep FastTrack for LAN to LAN
• Remove FastTrack from WAN bound traffic so QoS can act

2. Add Smart Queues on WAN and the bridge

• Start with FQ CoDel queues for upload and download
• Upgrade to CAKE for better flow isolation and easier tuning

Results

• Grade A with FQ CoDel
• Grade A+ with CAKE
• Added latency under load cut roughly in half

What FQ CoDel And CAKE Do

• FQ CoDel (FlowQueue Controlled Delay)
  • Combines fair queueing with CoDel’s delay-based drops
  • Keeps queue sojourn time low by dropping just enough packets to drain queues
  • Simple and effective
• CAKE (Common Applications Kept Enhanced)
  • Built on FQ CoDel with better defaults and features
  • Per host fairness modes (dual-srchost / dual-dsthost)
  • NAT aware (correctly identifies flows behind a router)
  • RTT schemes to fit typical paths (regional)
  • Easier to tune for “set it and forget it” operation

In practice CAKE gave me the same or better throughput with lower added latency under load and smoother behavior during bursts.

How I Configured It

Attach queues where queues form

• Upload: parent is the WAN interface
• Download: parent is the LAN bridge

Define queue types

• Start with FQ CoDel types for upload/download
• Then define CAKE types with:
  • NAT aware enabled
  • dual-srchost for upload, dual-dsthost for download
  • RTT scheme set to regional for low-latency links

Apply queue tree entries

• One entry on WAN for upload using the upload queue type
• One entry on the bridge for download using the download queue type

Set realistic limits

• Use max-limit a bit below your true line rate (for example 95 percent)
• This ensures the only meaningful queue is in your router, where CAKE can manage it

Keep FastTrack for LAN

• Modify the FastTrack rule so it matches only LAN to LAN traffic
• Leave WAN bound traffic out of FastTrack so it traverses the queue tree

Notes On Testing And Tuning

• Run the Waveform test multiple times to avoid one-off anomalies
• Look at added latency during both download and upload
• Rare spikes can still appear. Some come from outside your network
• If CPU becomes a bottleneck, reduce limits slightly or confirm hardware offload paths for non-shaped traffic

Results In My Network

• FQ CoDel moved me to Grade A
• CAKE moved me to Grade A+
• Added latency under load dropped from around 10ms to about 5ms
• Real time tools and calls became more stable under heavy transfers

Related

For UniFi radio settings that pair well with this, see my WiFi tuning notes: /blog/unifi-wifi-optimizations-for-better-bufferbloat-and-apple-devices