[ubuntu] Need help with iperf tests

I am running performance tests using iperf on virtual machines created using vagrant. One of my VMs acts as tcpclient where iperf client runs and the other one acts as tcp server where my iperf server runs

They are run using the following commands:

iperf3 -c 192.168.3.11 -t 1 -b 1G -> client

iperf3 -s -I 1 -> server


I have disabled checksum offloading on both the VMs

If I send traffic at low rates, things seems to be fine. But if I increase the traffic rate(500mbps/1gbps), iperf sends packets large sizes ie., beyond the MTU of the ethernet interface.
And when this happens, tcpdumps shows these packets with incorrect checksum

Shouldn't iperf/tcp automatically detect the MTU and adjust the segment sizes accordingly?


I even tried setting the segment size using --set-mss / packet length using -l options of iperf client. But none of these seems to work.
Can you please help point the issue?


Thanks!