iperf is a tool for measuring the maximum TCP and UDP bandwidth along
a path between two hosts.  It allows the tuning of various
parameters and UDP characteristics, and reports bandwidth, delay
jitter, datagram loss.  iperf was originally developed by NLANR/DAST.

iperf3 is a new implementation from scratch, with the goal of a
smaller, simpler code base, and a library version of the functionality
that can be used in other programs.  iperf3 also a number of features
found in other tools such as nuttcp and netperf, but were missing from
iperf 2.x.  iperf3 is not backwards compatible with iperf 2.x.

WWW: https://github.com/esnet/iperf