SSH tunneling/port-forwarding tricks

Here are a few tricks about SSH tunnels I don't want to forget.

Tunneling through a “jump host”

It is possible to access a service behind a firewall or NAT by using a public SSH server as a “jump host”.

A possible script to make connections to port 1234 of the “jump host” to be forwarded to port 80 of the host not publicly accessible is the following:


set -e



  "ssh -c none -g -L ${REMOTE_PUBLIC_PORT}:localhost:${LOCAL_SERVICE_PORT} ${LOCAL_USER}@localhost -p ${REMOTE_PRIVATE_PORT}"

Someone calls this approach “double tunneling”, here is a graphical explanation to make it stick into my memory:

SSH tunneling/port-forwarding through a “jump host”

Keep in mind that connections to port 1234 must be allowed by the firewall on the “jump host”, in my iptables setup (which uses a chain named in-new for new input connections), I'd do something like that:

sudo iptables -A $INPUT_CHAIN -p tcp -m tcp --dport $REMOTE_PUBLIC_PORT --tcp-flags FIN,SYN,RST,ACK SYN -j ACCEPT

In order to delete this single rule it is possible to list all the rules with this command:

 sudo iptables -v -n -L $INPUT_CHAIN --line-numbers

take note of the rule number, and then call:

sudo iptables -D $INPUT_CHAIN <rule number>

Tunneling to your IM contacts

SSH port forwarding can be combined with Telepathy and ssh-contact too.

For instance the command below makes your SSH server accessible to the local port 2222 of the contact you choose:

ssh-contact -- -l remote_ssh_user -R 2222:localhost:22

This other command makes the SSH server of your contact accessible on your local port 2222:

ssh-contact -- -l remote_ssh_user -L 2222:localhost:22

These kind of tricks can be useful if you want to do some file transfers via SCP/sftp, for example.


It's been a while since I did some networking stuff, so my terminology may sound a little off: I could have used “Jump Node” or “Relay Node” instead of “Jump Host”, let me know if you think there is room for improvement in the article or in the drawing.

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Respect. Thanks for the post.

Ritratto di Anonymous

Respect. Thanks for the post.

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