Reverse port forwarding can be referred to as reverse tunnel. Reverse
tunnel is a very useful way to access some application on the computer
that behind a restricted or tight Firewall/Gateway/Router. For security
concern, a lots of administrators will configure Firewall/Gateway/Router
to refuse the connection from outside. So you just can not directly
access those computers without reverse tunnel technology. Normally,
reverse tunnel include two components. One you can call client component
and the other is server component. You should deploy the client
component on the side of the computer that behind
Firewall/Gateway/Rourter and the server component on the side of your
computer. The client and server component will automatically create a
session connection to control reverse tunnel. The server component will
listen on a port that you can connect. So when you access the port of
server component. The server component will control the client component
to create a reverse tunnel connection to the server component. The
Firewall/Gateway/Router will not restrict this. Then client component
can receive data from server component and port forwarding to the
application on the computer that behind Firewall/Gateway/Router. This is
the basic idea of reverse tunnel that can let you access some
application that you can not directly access.
Easy but Powerful TCP and UDP Port Forwarding Tool (See our typical clients here)
Our port forwarding software is
made to be easy ... but powerful. This powerful port forwarding
tool will let you auto port forwarding until the destination ip address
is reached. Windows XP, Windows 2000, Vista, Windows 7 and MAC OSX are
all supported. The tool support all protocols based on TCP and UDP.
Integrating http proxy function will let all of your computers share the
same internet connection to surf internet. At the same time, it can
turn non-SSL aware software into safely software by using SSL tunnel
technology.
from http://www.port-forwarding.net/ 
