How to Create a Reverse Ssh Tunnel

Need to skirt around that pesky corporate firewall?

Or host a service while NATed?

What you need is a reverse SSH tunnel and you will be well on your way to confusing your friends trying to tell them what you've done.

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Steps

1. 1
   Server: apt-get install openssh-server
2. 2
   Server: ssh-keygen
   
   
3. 3
   Client: apt-get install openssh-client
4. 4
   Client: ssh-keygen
5. 5
   Client: ssh-copy-id user@server
   
   
6. 6
   Server: Edit /etc/ssh/sshd_config as root.
   • Change '#PasswordAuthentication yes' to 'PasswordAuthentication no'.
   • Add 'GatewayPorts clientspecified' to the end of the file.
     
     
     
7. 7
   Client: Now we create the reverse tunnel with
   ssh -R 10.0.0.111:5555:127.0.0.1:4444 user@10.0.0.111
   • -R makes the tunnel reversed
   • 10.0.0.1 is the ip address of the interface on your server that is facing the Internet
   • 5555  is the servers port to listen on.
   • 4444 is the port to forward to on your client.
8. 8
   Now you can open ports on the server to the Internet and forward them through your tunnel to your client.

 Tips

• Use -nNR when creating the tunnel if you don't need a shell.
• You can change the computer that the port is forwarded to by changing the local loop-back address (127.0.0.1) to the ip address of that computer. So, 10.0.0.111:5555:192.168.0.2:4444 would forward port 5555 on 10.0.0.111 to port 4444 on 192.168.0.2
  

  Warnings

• Keep the id_rsa file created by ssh-keygen safe! This is you private key! Give it to no one! id_rsa.pub however, you can give out to anyone.

Things You'll Need

• Two computers: One that you will be forwarding ports to and the other that you can open to the Internet.
• These instructions assume both systems are running Ubuntu or a similar distro.
• Basic knowledge of the command line might help.