Solved.
I had to enable "Packet Steering" on all CPUs.
iperf3 -c it1.speedtest.aruba.it -R -P 4
Connecting to host it1.speedtest.aruba.it, port 5201
Reverse mode, remote host it1.speedtest.aruba.it is sending
[ 5] local 79.46.219.163 port 39500 connected to 31.14.130.68 port 5201
[ 7] local 79.46.219.163 port 39512 connected to 31.14.130.68 port 5201
[ 9] local 79.46.219.163 port 39514 connected to 31.14.130.68 port 5201
[ 11] local 79.46.219.163 port 39518 connected to 31.14.130.68 port 5201
[ ID] Interval Transfer Bitrate
[ 5] 0.00-1.00 sec 48.6 MBytes 407 Mbits/sec
[ 7] 0.00-1.00 sec 51.8 MBytes 434 Mbits/sec
[ 9] 0.00-1.00 sec 42.6 MBytes 357 Mbits/sec
[ 11] 0.00-1.00 sec 50.2 MBytes 421 Mbits/sec
[SUM] 0.00-1.00 sec 193 MBytes 1.62 Gbits/sec
- - - - - - - - - - - - - - - - - - - - - - - - -
[ 5] 1.00-2.00 sec 49.8 MBytes 417 Mbits/sec
[ 7] 1.00-2.00 sec 48.1 MBytes 404 Mbits/sec
[ 9] 1.00-2.00 sec 52.1 MBytes 437 Mbits/sec
[ 11] 1.00-2.00 sec 50.8 MBytes 426 Mbits/sec
[SUM] 1.00-2.00 sec 201 MBytes 1.68 Gbits/sec
- - - - - - - - - - - - - - - - - - - - - - - - -
[ 5] 2.00-3.00 sec 52.1 MBytes 437 Mbits/sec
[ 7] 2.00-3.00 sec 46.5 MBytes 390 Mbits/sec
[ 9] 2.00-3.00 sec 47.6 MBytes 399 Mbits/sec
[ 11] 2.00-3.00 sec 54.8 MBytes 459 Mbits/sec
[SUM] 2.00-3.00 sec 201 MBytes 1.69 Gbits/sec
- - - - - - - - - - - - - - - - - - - - - - - - -
[ 5] 3.00-4.00 sec 48.5 MBytes 406 Mbits/sec
[ 7] 3.00-4.01 sec 45.8 MBytes 382 Mbits/sec
[ 9] 3.00-4.01 sec 45.4 MBytes 379 Mbits/sec
[ 11] 3.00-4.01 sec 52.1 MBytes 436 Mbits/sec
[SUM] 3.00-4.00 sec 192 MBytes 1.60 Gbits/sec
- - - - - - - - - - - - - - - - - - - - - - - - -
[ 5] 4.00-5.00 sec 49.1 MBytes 414 Mbits/sec
[ 7] 4.01-5.00 sec 44.6 MBytes 376 Mbits/sec
[ 9] 4.01-5.00 sec 42.6 MBytes 359 Mbits/sec
[ 11] 4.01-5.00 sec 50.0 MBytes 421 Mbits/sec
[SUM] 4.00-5.00 sec 186 MBytes 1.57 Gbits/sec
- - - - - - - - - - - - - - - - - - - - - - - - -
[ 5] 5.00-6.00 sec 49.9 MBytes 418 Mbits/sec
[ 7] 5.00-6.00 sec 43.6 MBytes 366 Mbits/sec
[ 9] 5.00-6.00 sec 44.6 MBytes 374 Mbits/sec
[ 11] 5.00-6.00 sec 49.6 MBytes 416 Mbits/sec
[SUM] 5.00-6.00 sec 188 MBytes 1.57 Gbits/sec
- - - - - - - - - - - - - - - - - - - - - - - - -
[ 5] 6.00-7.00 sec 52.8 MBytes 443 Mbits/sec
[ 7] 6.00-7.00 sec 48.8 MBytes 409 Mbits/sec
[ 9] 6.00-7.00 sec 44.6 MBytes 374 Mbits/sec
[ 11] 6.00-7.00 sec 49.4 MBytes 414 Mbits/sec
[SUM] 6.00-7.00 sec 196 MBytes 1.64 Gbits/sec
- - - - - - - - - - - - - - - - - - - - - - - - -
[ 5] 7.00-8.00 sec 47.6 MBytes 399 Mbits/sec
[ 7] 7.00-8.00 sec 48.6 MBytes 407 Mbits/sec
[ 9] 7.00-8.00 sec 43.9 MBytes 368 Mbits/sec
[ 11] 7.00-8.00 sec 49.4 MBytes 414 Mbits/sec
[SUM] 7.00-8.00 sec 190 MBytes 1.59 Gbits/sec
- - - - - - - - - - - - - - - - - - - - - - - - -
[ 5] 8.00-9.00 sec 46.9 MBytes 393 Mbits/sec
[ 7] 8.00-9.00 sec 47.5 MBytes 399 Mbits/sec
[ 9] 8.00-9.00 sec 47.1 MBytes 396 Mbits/sec
[ 11] 8.00-9.00 sec 49.2 MBytes 414 Mbits/sec
[SUM] 8.00-9.00 sec 191 MBytes 1.60 Gbits/sec
- - - - - - - - - - - - - - - - - - - - - - - - -
[ 5] 9.00-10.00 sec 50.9 MBytes 427 Mbits/sec
[ 7] 9.00-10.00 sec 46.9 MBytes 393 Mbits/sec
[ 9] 9.00-10.00 sec 45.4 MBytes 381 Mbits/sec
[ 11] 9.00-10.00 sec 50.1 MBytes 420 Mbits/sec
[SUM] 9.00-10.00 sec 193 MBytes 1.62 Gbits/sec
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval Transfer Bitrate Retr
[ 5] 0.00-10.00 sec 524 MBytes 440 Mbits/sec 10658 sender
[ 5] 0.00-10.00 sec 496 MBytes 416 Mbits/sec receiver
[ 7] 0.00-10.00 sec 504 MBytes 423 Mbits/sec 9915 sender
[ 7] 0.00-10.00 sec 472 MBytes 396 Mbits/sec receiver
[ 9] 0.00-10.00 sec 485 MBytes 407 Mbits/sec 10644 sender
[ 9] 0.00-10.00 sec 456 MBytes 382 Mbits/sec receiver
[ 11] 0.00-10.00 sec 534 MBytes 448 Mbits/sec 10722 sender
[ 11] 0.00-10.00 sec 506 MBytes 424 Mbits/sec receiver
[SUM] 0.00-10.00 sec 2.00 GBytes 1.72 Gbits/sec 41939 sender
[SUM] 0.00-10.00 sec 1.89 GBytes 1.62 Gbits/sec receiver
iperf Done.
Thanks