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I have the following setup:

  • Raspberry Pi with no public IP address
  • Public "jumpserver"

Currently i have autossh running on the Raspberry to connect to the jumpserver.

Works without problems. I connect to the jumpserver via ssh and from there via ssh to the Raspberry Pi.

Now i want to add a VNC client on the Raspberry to the game so i can directly connect to it from my local machine. My plan would be:

  • Start VNC on the Raspberry (Port 5901)
  • Make an connection with autossh to create a reverse tunnel between localhost:5901 and jumpserver:1702
  • Create iptable-entries on the jumpserver to forward incoming traffic on port 5555 to localhost:1702

The first question is: Could this work like this? Not sure about the vnc port on the Raspberry being the same as the local port auf autossh. Or would i need another local port for autossh and also use iptables on the Raspberry to forward the incoming traffic from autossh to the VNC port?

Any help is appreciated.

Thank you

I already created iptable entries on the jumpserver like this, but it doesnt work:

sudo iptables -t nat -A PREROUTING -p tcp --dport 5555 -j DNAT --to-destination 127.0.0.1:1702
sudo iptables -t nat -A POSTROUTING -p tcp -d 127.0.0.1 --dport 1702 -j SNAT --to-source 127.0.0.1:5555

1 Answer 1

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The use of DNAT-to-localhost is somewhat redundant given that you could just as well have the SSH tunnel listen on 0.0.0.0:5555 directly. (To allow this, enable GatewayPorts on the listening side of the tunnel, i.e. on the jumpserver's sshd_config – GatewayPorts clientspecified will allow you to specify the listening address as part of the ssh -R option.)

Redundancy aside, the DNAT rule seems like it would work (there is in fact even a REDIRECT target specifically for NATing to localhost).

On the other hand the SNAT rule is useless, and it seems like you're confusing how source/destination ports work. A connection made to port 5555 does not need to come from port 5555 (it's only the reply packets that do; keep in mind that iptables NAT will automatically handle reverse NAT for reply packets).

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