iperf3 - unable to connect to server: Connection refused

Is there any flag to override this?

In iperf2, I'm able to send a stream of UDP data to an IP address using a command like:

iperf -c <remote_ip> -u -b 100M -n 5G 

I'm trying to use the latest version, which is iperf3.

I'm trying to conduct throughput tests, where there isn't an iperf process at the other end. I can send a bunch of UDP data to an IP address at the other end of the link. Then using netflow statistics, I can see the throughput speed of the link.

This works fine for iperf (v2). However I can't see a flag in iperf3 to ignore a missing server. Does this not exist in iperf3 (to avoid it being used as a denial of service tool?)

(I've been looking through the iperf support forums on sourceforge, can't find this question addressed.)