How to set the UDP Packet Size with iperf3? The flag "-M" does not work with iperf3. Is there an alternative?

2 Answers 2


-l is the suitable option for or UDP packet size in iperf3

not -M (which is MSS for TCP)


There isn't a way to do it directly in iperf3. However, you can adjust down the MTU size set on your network interface, and iperf will respect that. So long as you're looking to set your packet-sizes smaller than the actual network MTU, that is.

  • but then the packets get fragmented..
    – Jimmy88
    Nov 6, 2016 at 16:42

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