[DarkDelta]

Hello and welcome to this small tutorial.

What is reverse tunneling?

Reverse tunneling is connecting a server behind a inbound-blocking firewall to another server or computer.
Wikipedia article about reverse connections: http://en.wikipedia.org/wiki/Reverse_connection

see it like this:

Source = random, non firewalled, server
Destination = the firewalled server (e.g. home computer)
PC = well...you know that.

you connect like this:

PC -> Source <- Destination

So, if you for instance, create a port 80 tunnel to browse the webserver on the Destination, and use the local port 2000 on the Source, it will look like this.

PC -> Source:2000 <- Destination:80

port 2000 is the tunnel to port 80.

But, how do i do this?

Step 1:
Edit your sshd_config file (usually found in /etc/ssh)

Add below "Port 22"

Code

GatewayPorts yes

then issue:

Code

Ubuntu:
/etc/init.d/sshd restart

Arch:
/etc/rc.d/sshd restart

Step 2:
Set up the tunnel

Code

ssh -R source_port:localhost:destination_port user@source

Let's break it down.

ssh
The SSH Client Command

-R
Reverse Connection

source_port:localhost:destination_port

it will look something like this..

Code

2000:localhost:80

..if you want to forward port 2000 to port 80.

You can do this with port 22 (SSH) too.

Code

2000:localhost:22

then on the source server, ssh to:
ssh -l destination_user -p 2000 localhost

now you are ssh'ing into the destination server, where otherwise it would have been impossible.

if you're on another computer, and you normally SSH into your source server via port 22, you can now SSH into your destination server via SSH too, just connect to source server's hostname or IP and then port 2000 (or other when you've changed it.)

user@source
the connection info to where the tunnel should lead.
e.g.

Code

[email protected]

I hope you have learned from this.

to see the tunnel in action:
http://n01p.com:2001/~remon/microtime.php

yes, that runs on a firewalled server, normally unreachable from the outside.

[Ui Hirasawa]

Good tutorial, will be useful!

[Alison Wonderland]

Could you explain this (what it is usefull for)
i didnt quite understand the wikipedia explanation