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Tunneling, or port forwarding, is a way to forward otherwise insecure TCP traffic through an encrypted Secure Shell tunnel. You can secure for example POP3, SMTP and HTTP connections that would otherwise be insecure.
Note: The client-server applications using the tunnel will carry out their own authentication procedures (if any) the same way they would without the encrypted tunnel.
The tunneling capability of SSH Secure Shell for Workstations is a feature that allows, for example, company employees to access their email, company intraweb pages and shared files securely by even when working from home or on the road.
Tunneling makes it possible to access email from any type of Internet service (whether accessed via modem, a DSL line or a cable connection, or a hotel Internet service). As long as the user has an IP connection to the Internet she can get her mail and access other resources from anywhere in the world securely.
This often is not the case with more traditional IPSec based VPN technologies because of issues with traversing networks that are implementing Network Address Translation (NAT) - this is especially the case in hotels. NAT breaks an IPSec connection unless special protocols such as NAT-Traversal are implemented on the client and gateway.
The client-server applications using the tunnel will carry out their own authentication procedures, if any, the same way they would without the encrypted tunnel.
The protocol/application might only be able to connect to a fixed port number ( e.g. IMAP 143). Otherwise any available port can be chosen for port forwarding.
Local And Remote Forwarding
There are two kinds of port forwarding: local and remote forwarding. They are also called outgoing and incoming tunnels, respectively.
Local port forwarding forwards traffic coming to a local port to a specified remote port. For example, all traffic coming to port 1234 on the client could be forwarded to port 23 on the server (host).
Note: The value of localhost is resolved after the Secure Shell connection has been established - so when defining local forwarding (outgoing tunnels), localhost refers to the server (remote host computer) you have connected to.
Remote port forwarding does the opposite: it forwards traffic coming to a remote port to a specified local port. For example, all traffic coming to port 1234 on the server (host) could be forwarded to port 23 on the client (localhost).
The tools that we need make a tunnel by using remote termal client such as http://www.vandyke.com/products/securecrt/ or putty
by visiting there you are also get an information how to do tunneling
