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"Firewall Tunnelling using SSH & Putty"

SSH (Secure Shell) is a protocol that allows two devices to connect and exchange data securelyin an encrypted format. It usually uses the port 22 for all communication. It protects your sensitive information like username and password by encrypting it and securely transmitting it over internet.
PuTTY is a free, open source client that allows users to establish connections using SSH, Telnet etc. with remote systems. To download it, click here. It will open a window like this...

Let us assume that you are connected to the internet and are behind the firewall of your college or company that doesn't allow you to make outgoing connections to remote Port 80 (HTTP or websites) of a particular website, say facebook. Just because the firewall has blocked access to remote Port 22, it doesn't mean that it would have also blocked outgoing connection to remote Port 22 (SSH). This means that you may be able to use PuTTY to create a SSH Tunnel connection through the firewall (outgoing remote Port 22) to a remote SSH server that you have access to and then use this remote SSH server to connect to the blocked remote systems. In other words, your firewall thinks that you are connecting to Port 22 of a harmless system, but in reality you are using that system to connect to facebook. The process is shown in following steps:-

STEP 1:-

You need to either set up your own SSH server with unblocked Internet access or register an account on a SSH server that has unblocked access to the Internet. This SSH server can be in any part of the world.

STEP 2:-

Use PuTTY to create an encrypted SSH connection to the remote SSH server. (Outgoing Port 22, encrypted communication will be allowed by most local firewalls.) PuTTY opens a local Port that you can now connect to in order to access the remote SSH server.

STEP 3:-

Once you have connected to remote SSH server that has unblocked access to the Internet, you can then use it to access all your favourite websites on the internet.

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Let us assume that your firewall has blocked outgoing connections to remote Port 25 and 80 and you want to use PuTTY and SSH to bypass this Blocking mechanism. Now follow the steps to do this...

STEP 1:-

Download PuTTY and click on Session. In the hostname field enter the IP address of the SSH server that you want to connect to. In the port field enter 22.

STEP 2:-

Click on connection>SSH>Tunnels and enter the IP address and Port numbers of the blocked remote systems you wish to tunnel to. For example, I entered 110 in the source port field & 192.168.0.11:110 in the destination field then clicked on ADD. It will look like this...

STEP 3:-

Based on this configuration, now the local port 80 on your system will connect to port 80 on 190.168.0.1 (using SSH connection to SSH server) and the local port 25 will connect to Port 25 on 192.168.0.22 and so on. As simple as that.

STEP 4:-

Now click on the OPEN button, you will be prompted to enter the SSH server username and password. You would have received it when you created an account on the remote SSH server. PuTTY now starts to listen to port 80 and port 110 on the local system. Now in order to access the port 80 on 192.168.0.1, you need to start your browser or any other tool and simply type local host: 80 or local host: 110 & press enter! It is also possible to buy SSH Tunnel accounts on various websites like "https://camolst.com/sshtunnel/" which is currently providing a SSH tunnel account to users at a subscription price of $5 per month.

If all goes well you will be able to get the internet access through tunneling and till you want. If you have any queries please ask it into comments.

Thank you