What it is¶

flent (the FLExible Network Tester) wraps netperf (and other tools such as iperf) to run scripted tests and plot the results. It is the standard tool for measuring bufferbloat: how much latency rises when a link is saturated. Throughput tests like iperf will not show that.

Setup¶

The far end needs a running netserver (from the netperf package). The near end needs flent:

sudo apt-get install flent netperf        # client
netserver                                 # on the remote host (listens on TCP 12865)

The RRUL test¶

RRUL (Realtime Response Under Load) saturates the link in both directions with several TCP flows while measuring latency with UDP/ICMP probes.

flent rrul -p all_scaled -l 60 -H netserver.example.com -t "wan-baseline" -o rrul.png

Run it once with your normal queue settings and again after enabling a smart queue discipline such as fq_codel or cake (tc qdisc replace dev eth0 root fq_codel) to see the difference. Results are saved as .flent.gz data files that can be re-plotted later.