Question

Trouble connecting through SSH tunnel to Droplet

I have an SSH tunneling scheme which works on my local cluster but has connection failures when I try to use it on my Ubuntu droplet. I set up the tunnel in SSH from my local machine like this:

ssh -L 12003:127.0.0.1:12003 NYTrader -N

NYTrader is defined in my config with the droplet IP and user root. That command works apparently - from my droplet:

root@NYTrader:~# ss -tuln
Netid      State       Recv-Q      Send-Q           Local Address:Port              Peer Address:Port      Process
udp        UNCONN      0           0                   127.0.0.54:53                     0.0.0.0:*
udp        UNCONN      0           0                127.0.0.53%lo:53                     0.0.0.0:*
tcp        LISTEN      0           4096             127.0.0.53%lo:53                     0.0.0.0:*
tcp        LISTEN      0           4096                127.0.0.54:53                     0.0.0.0:*
tcp        LISTEN      0           1                      0.0.0.0:12003                  0.0.0.0:*
tcp        LISTEN      0           4096                         *:22                           *:*
root@NYTrader:~#

I have a script on the droplet sending characters every 2 seconds on 12003.

From my local PC:

 telnet 127.0.0.1 12003
Trying 127.0.0.1...
telnet: Unable to connect to remote host: Connection refused

Why is this connection refused? The tunnel appears to be up?


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Accepted Answer

Not sure where I went wrong - but it’s working now. Thanks for the replies

Bobby Iliev
Site Moderator
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June 13, 2024

Hey!

Does the telnet 127.0.0.1 12003 command work as expected when you run it on the Droplet itself?

The command you’ve used for the SSH tunnel seems fine, but can you confirm that NYTrader is correctly defined in your SSH config file? It should look something like this:

Host NYTrader
    HostName <Droplet_IP>
    User root
    Port 22

Another thing that you could test out is that there is no firewall rule on your local machine that could be blocking outgoing connections to localhost:12003. You can test that quickly with telnet portquiz.net 12003

Let me know how it goes!

- Bobby

KFSys
Site Moderator
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June 13, 2024

Heya,

The SSH tunneling setup you described should allow you to forward traffic from port 12003 on your local machine to port 12003 on the remote machine (NYTrader). The fact that ss -tuln shows tcp LISTEN 0 1 0.0.0.0:12003 0.0.0.0:* on the remote machine means that the port 12003 is indeed open and listening on all interfaces (0.0.0.0).

However, the connection refused error when you attempt to telnet to 127.0.0.1:12003 on your local machine indicates that the tunnel might not be properly forwarding the traffic or there could be some other issue preventing the connection.

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