Asymmetric speed w/ SSH Port Forwarding

[Clément Péron]

Hi,

I was trying to have a SSH tunnel with at least 150Mbps/s in both directions.

I have a laptop computer under Ubuntu 20.04.2 and a remote server also
under Ubuntu 20.04.2.

I measured the speed of my internet connection with Iperf3 and without
SSH Tunnel it is OK.
$> iperf3 -c <SERVER_IP> -p 7503
- 500 Mbits/sec laptop -> server
$> iperf3 -c <SERVER_IP> -p 7503 -R
- 927 Mbits/sec laptop <- server

Then I open a SSH Tunnel: laptop -> server
$> ssh -L 7503:127.0.0.1:7503 root at my_server

Doing the iperf3 test again
$> iperf3 -c 127.0.0.1 -p 7503
- 13.6 Mbits/sec
$> iperf3 -c 127.0.0.1 -p 7503 -R
- 672 Mbits/sec

And now the speed is terrible from my laptop to the server.

In the iperf console this looks like this
[ ID] Interval           Transfer     Bitrate         Retr  Cwnd
[  5]   0.00-1.00   sec  11.2 MBytes  94.3 Mbits/sec    2   1023 KBytes
[  5]   1.00-2.00   sec  0.00 Bytes  0.00 bits/sec    1    639 KBytes
[  5]   2.00-3.00   sec  1.25 MBytes  10.5 Mbits/sec    0    639 KBytes
[  5]   3.00-4.00   sec  0.00 Bytes  0.00 bits/sec    0    639 KBytes
[  5]   4.00-5.00   sec  1.25 MBytes  10.5 Mbits/sec    0    639 KBytes
[  5]   5.00-6.00   sec  0.00 Bytes  0.00 bits/sec    0    639 KBytes
[  5]   6.00-7.00   sec  1.25 MBytes  10.5 Mbits/sec    0    639 KBytes
[  5]   7.00-8.00   sec  0.00 Bytes  0.00 bits/sec    0    639 KBytes
[  5]   8.00-9.00   sec  0.00 Bytes  0.00 bits/sec    0    639 KBytes
[  5]   9.00-10.00  sec  1.25 MBytes  10.5 Mbits/sec    0    639 KBytes

During some seconds there is no Bitrate at all :(.

I understand that the SSH tunnel will add some overhead and I will
lose around 10/20% of Bandwidth but this looks like a huge drop.

Do you have any idea what can create this behavior?

Thanks for your help,
Clement