See Set Up SSH Keys.

ssh -v ...

Take care of both with this one-liner:

On the Client PC:

echo "Host *
        ServerAliveInterval 60
        GSSAPIAuthentication=no" >> $HOME/.ssh/config

(be sure to copy and paste everything including the CRLF's and spaces)

If a permissions error is thrown:

chmod 600 /home/gcooper/.ssh/config

If you get an error message “unknown terminal type”, you can try specifying a different terminal like this:

TERM=xterm-color ssh -l username remote.host.name

Adjust your firewall first or you may lose access!

vim /etc/ssh/sshd_config

Port 2222

service sshd restart

http://www.howtoforge.com/reverse-ssh-tunneling

http://www.alexonlinux.com/reverse-ssh-tunnel-or-connecting-to-computer-behind-nat-router

This technique is used to access an SSH host behind a NAT firewall using a middle-man PC with a static IP address.

• Box behind NAT creates a reverse tunnel connection to the middle-man
• User connects to middleman PC on reverse tunnel port

On the middle-man host with a real static IP address:

• Set “GatewayPorts yes” in /etc/ssh/sshd_config
  • Restart sshd if sshd_config changed
• Configure to use SSH keys rather than passwords
  • Less trouble
  • More secure

On remote host (behind NAT) that you want to access:

ssh -R 22222:localhost:22 root@middleman

or if SSH is listening on a non-standard port:

ssh -R 22222:localhost:22 root@middleman -p 2222

From your workstation, connect through the middle-man PC:

ssh -p 22222 root@middleman

http://www.howtoforge.com/reverse-ssh-tunneling#comment-4762

Use AutoSSH to keep a tunnel up constantly.