This is my method to keep connected with a remote Raspberry Pi that has a static external IP address and lives behind a NAT, where I don’t have control over the router (so no port forwarding). For your use case, you might want to choose another method (there are plenty on the world wide web, I’m sure you can find them), but the simple method below works for me.
on Base
Create a new user with adduser tunnel
user tunnel
pass SomeComplicatedPass
You need a modification to sshd_config. At the end of the file, add a Match block to prevent password-based logins (only allow keybased logins for user tunnel) so the password above is of little use to the outside world
# Match blocks must be at the and of this config file, see:
# http://unix.stackexchange.com/questions/67334/openssh-how-to-end-a-match-block
Match User tunnel
PasswordAuthentication no
on Hunter
Login to Hunter. I assume evert as your username on Hunter
Create the reverse tunnel using:
ssh -N -R 2222:localhost:22 tunnel@Base
Or, more sophisticated:
autossh -M 0 -q -f -N \
-o UserKnownHostsFile=/dev/null \
-o StrictHostKeyChecking=no \
-o "ServerAliveInterval 60" \
-o "ServerAliveCountMax 3" \
-R 2222:localhost:22 \
tunnel@Base
This can be done best by doing it from cron and with a script.
crontab -e
@reboot /home/evert/tunnel.sh 60
My script is named tunnel.sh.
You can download my files: reverse_ssh_tunnel.zip
Usage
First login to Base, then connect to Hunter using:
ssh evert@Base
ssh localhost -p 2222
And from there, you can play with Hunter.
Have fun!
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