tcpbench(1) on OpenBSD
The text 4eccd0310bef, as OpenBSD 6.6, OpenBSD 6.5, OpenBSD 6.4 shipped it.
TCP/UDP benchmarking and measurement tool
Flags it lists
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-4 -
-6 -
-B -
-R -
-S -
-T -
-U -
-V -
-b -
-k -
-l -
-n -
-p -
-r -
-s -
-t -
-u -
-v