iperf3 reverse switch with no response

iperf3 reverse switch with no response

I have a requirement to run an iperf server instance on one of our
servers, and during testing our product will connect to the server to
check bandwidth. Client->Server comms works fine in both iperf (2.0.4) and
iperf3, but dualtest/tradeoff (v2) or reverse (v3) fail to do much of
anything when I try to test Server->Client comms.
Reverse output - Server
$ iperf3 -s
-----------------------------------------------------------
Server listening on 5201
-----------------------------------------------------------
Accepted connection from CLIENT, port 37636
[ 5] local SERVER port 5201 connected to CLIENT port 37637
Client
$ iperf3 -c SERVER -f M -n 10M -R
Connecting to host SERVER, port 5201
[ 4] local CLIENT port 37637 connected to SERVER port 5201
As far as I can tell nothing happens from here until I interrupt the
server. If I interrupt the client before the server it spits out many
lines of
iperf3: error - unable to start listener for connections: Address already
in use
iperf3: error - unable to start listener for connections: Address already
in use
iperf3: error - unable to start listener for connections: Address already
in use
If anyone has experienced this sort of nastiness with iperf before I would
really appreciate some insight.