What is it exactly?
The ADSL or Cable routers/modem that are used to connect to the internet are NAT enabled Firewalls.They protect the devices connected to them from unauthorized access from devices on the internet.I have used the term “devices” since it could be a computer, mobile or laptop with WiFi access etc. They group the devices behind the router into a private network and assign them a separate range of I.P. address (generally starting with 192.168). While the router itself has a public I.P. Address assigned by the Internet Service Provider (called as Internet address).
When a service from within the private network makes a request to a service on a remote network (e.g. a browser requesting a webpage on the Internet) an entry is created for that particular server in the NAT table maintained by the router.The device can only receive a response from the server for which it has made a request.It cannot receive requests / responses from any device whose entry is not present in the NAT table.
So what should you do a if you want to run a web server or a FTP server or any other service which you want to access from an external network like Internet.How would you access that particular service ?
The answer is Port forwarding or Port Mapping.Basically you create an exception within the NAT table of the router by opening some of its ports.You tell the router to accept all the requests to a particular I.P. and to a particular port.After you have done this the service running at that particular port will be accessible from any remote device.
Port Forwarding is recommended for Bittorent users.The port on which the torrent client (like utorrent or transmission) runs should be port forwarded to get more peers and achieve better download speed
Steps to PortForwading :
1. You need to assign a Static IP to your computer or device on which the service is going to run.The IP Address should be in the same range of your router.Suppose if your router has IP 192.168.1.1 then your computer should be assigned IP in the range 192.168.1.2 – 192.168.1.254.
How to assign static I.P. on various device
2. Now using the routers interface we have to forward the port.Every router has a different interface but the process is pretty much the same.
Visit this link to find the guide specific to your router. If you are unable to find your router you can log into your router and find port forwarding settings under names like “NAT Rule”,”Virtual Server”,”Port Forwarding”. Many routers even have similar interface to other routers, so you can follow the procedure for the same.
3.If you have been able to successfully forward the specific port you can check it by visiting this link. Before checking see to it that the service is currently running at the configured port.
Simply Thats All .
Please comment if you find this tutorial useful.