Port Forwarding, what is it?

[AboveTheLogic]

First, before understanding why and how to forward ports, it is important to understand what a NAT IP is vs. an Internet IP:

[url]http://forum.whatismyip.com/f2/internet-ip-vs-local-ip-t100/[/url]

Specifically the part in bold.

Now, it is important to understand what ports are. We are not talking about physical ports that you will find on the back of your computer. What we are talking about are virtual ports that exist as part of the [url="http://en.wikipedia.org/wiki/Network_port"]TCP/IP and UDP[/url] protocols.

There are 65536 ports ranging from 0-65535.

The most [url="http://en.wikipedia.org/wiki/List_of_TCP_and_UDP_port_numbers"]commonly used ports[/url] are the lower numbered ports.

I'll use Windows' [url="http://en.wikipedia.org/wiki/Terminal_Services#Remote_Desktop_Connection"]Remote Desktop Connection[/url] as an example (also known as Terminal Services).

The service, Terminal Services, listens (by default) on port 3389. When you open the Remote Desktop Client (run command "mstsc) and type in an IP, by default, the client will attempt to connect to that IP on port 3389.

When you put in an Internet IP, unless your computer is connected directly to a cable modem without [url="http://en.wikipedia.org/wiki/Network_address_translation"]NAT[/url], this should all work just fine and dandy.

When you are behind a router or a modem that IS using NAT, you need to [url="http://en.wikipedia.org/wiki/Port_forwarding"]forward the port[/url] to the local IP address.

The reason for this is, the router will receive the connection, but obviously the router itself isn't equipped to handle that request. The router needs to know which machine on your Local Area Network (or [url='http://en.wikipedia.org/wiki/Local_area_network"]LAN[/url]) to send the request to, this is why port forwarding is necessary.

Obviously to some, not to others, the router can only forward this request to ONE PC at a time. So, if you are running more than one machine, you will need to change the default port and forward it as necessary, or simply use a [url="http://en.wikipedia.org/wiki/Virtual_private_network"]VPN[/url].

If you do not know how to do the actual port forwarding configuration with your router, I find that there are usually instructions on the manufacturer's website with pictures and everything

[aziernest]

Pretty good, just wanted to say thanks for sharing

[oshantoshagorr@gmail.com]

thanks a lot.

[fsmobilez]

Nice post thanks for sharing such a useful post

[romantic]

I hope this will be useful
These routers do port forwarding by assigning port numbers to a "service" that is associated with the application you want to run.

To Let an Application Use Port Forwarding

1. Type the router's address in an Internet browser's address bar. (By default the router's address is 192.168.0.1). The Setup Wizard appears.
2. Enter the router's username and password.
3. Under Advanced, click Port Forwarding on the left menu bar.
A Port Forwarding Screen (Varies Slightly by Router)

4. From the Service & Game (or Service Name) pull down, select the service that you will host. The services the router knows about are listed here. If the service does not appear in the drop down, add a service as described in the next section, then return to this step.
5. Enter the IP address of your local server in the Server IP Address box.
6. Click Add.
7. Click Logout to exit from router settings.

To Add a Service for These Routers

To define a service not in the Service Name list, determine what port numbers are used by the service.

1. Click Add Custom Service.
2. Enter the first port number in an unused Start Port box.
3. If only one port number is to be forwarded, enter the same number in End Port. To specify a range of ports, enter the last port to be forwarded in the End Port box.
4. Enter any name you choose for the service.
5. Click Apply.

[zaidis]

Thanks its nice information.