UDP without don't-fragment?

[jlearman]

I'm trying to use iperf3 to measure the impact of IP fragmentation on a router. Unfortunately, iperf3 sets the IP "don't fragment" flag. How can I get iperf3 to send UDP/IP packets without the IP don't-fragment flag set?

I see that at https://www.mankier.com/1/iperf3 , there is a --dont-fragment flag. But if don't-fragment is on by default, how do I disable it?

I see that in UDP mode, iperf3 is "PMTUD-aware" and will adjust its buffer sizes based on PMTUD, which I obviously do not want. I see no way to disable this feature either.

I'm using iperf 3.10.1 (cJSON 1.7.13)

[jlearman]

Sorry, the DF bit is not being set. Never mind!

I do see that if the -l parameter is less than the path MTU, it sets DF. It would be nice to not do that, or have a way to override it.