What is Port Forwarding?
Port forwarding is the process that your router or firewall uses to sort the right kind of network data to the right port. Computers and routers use ports as a way to organize network data. Different types of data, such as web sites, file downloads, and online games, are each assigned a port number. By using port forwarding, the router or firewall sends the correct data to the correct place. A firewall protects your computer by blocking unauthorized information. If a firewall blocked all the incoming and outgoing data, the computer would be unable to access the Internet. When you want some data to go through your firewall, and you want it sent to a specific location, you can set up port forwarding. Port forwarding gives the firewall instructions about which types of data are allowed and how they should be directed. Information on the Internet is associated with a port. Web pages, for example, are typically assigned port 80. File transfer protocol (FTP), often used for downloading and u
Port forwarding, also referred to as tunneling, is essentially the process of intercepting traffic bound for a certain IP/port combination and redirecting to a different IP and/or port. This redirection may be accomplished by an application running on the destination host, or it may be performed by intermediate hardware, like a router, proxy server or firewall. Normally, a routing device will look at the header of a packet and simply send it to the appropriate interface to reach the destination it finds in the header. In port forwarding, however, the intercepting application or device reads the packet header, notes the destination, but rewrites the header information and sends it to a another host destination, different from the one requested. That host destination may be a different IP using the same port, a different port on the same IP, or completely different combination of the two. In the example below, 10.0.0.1 sends a request to 10.0.0.3 on port 80. An intermediate host, 10.0.0.
There are a couple of concepts you need to know before you can understand port forwarding. I’m going to make a couple broad statements that are almost always true. For simplicity lets assume they are true for now. 1.) Every device on the internet has at least one ip address. The IP address is a number that is used to identify a device. For more information on ip addresses refer to our What is an IP Address page. 2.) Every IP address is divided up into many ports. When one computer sends data to another computer, it sends it from a port on an ip address to a port on an ip address. For more information on ports refer to our What is a Port page. 3.) A port can only be used by one program at a time. Now that we’ve got those general concepts out of the way let’s talk about NAT. NAT is an acronym for Network Address Translation. NAT takes one ip address and basically breaks it into many ip addresses. Here the external ip address is broken into two internal ip addresses. The first ip address
