What is Port Forwarding.? How does it works.?

Since an IP address can easily be traced by anyone, most people prefer using services, like VPN or proxies to hide or change their IP address. These services employ the Port forwarding feature to change the IP address of any device.

Port forwarding, also referred to as Port tunneling, is a behind-the-scenes process of intercepting data traffic heading for a computer’s IP combination and redirecting it to a different IP. Usually, a VPN or proxy program is used to cause the redirection, but it can also be done via hardware components such as a router, proxy server, or firewall.

This allows you to send requests to servers across the internet without other people knowing the original location or IP address of these requests, guaranteeing your privacy on the internet.

How does port forwarding work?

To send any request over the internet, packets of data are created and sent over the internet. These packets contain the details of your request, which also includes the destination of your computer or device.

Normally, a network router examines the header of an IP packet before sending it to any linked and appropriate interface. It, in turn, then sends the data to the destination that’s in the header.

But Port forwarding changes things a bit. In port forwarding, the intercepting application (your VPN client) reads the packet header, notes down the destination, and then rewrites the header information before sending it to another computer or server—one which is different from the computer/server you intended.

That secondary host destination may be a different server using a different IP address, a different port, or a completely different combination of the two. In case of a VPN or proxy, this secondary destination are usually the servers employed by the provider which mask or cover your original IP address.

A look at port forwarding

The following example will help in explaining how the port forwarding feature works.

In the following example, IP Address 101.0.0.1 sends a request to 101.0.0.3 on Port 90. An intermediary host—101.0.0.2—intercepts the packets, rewrites the packet headers and sends them on to IP Address 101.0.0.4 on Port 9090:

101.0.0.1	–>	101.0.0.2	–>	101.0.0.4
	Makes a request to		Actually sends to
	101.0.0.3:90		101.0.0.4:9090

The host, 101.0.0.4, responds to this request, sending it to 101.0.0.2. Then 101.0.0.2 rewrites the packet—indicating that the response is from 101.0.0.3—and sends it to 101.0.0.1:

101.0.0.4	–>	101.0.0.2	–>	101.0.0.1
	Sends its response to		Forwards the response to
	101.0.0.2:9090		101.0.0.1:90

As far as 101.0.0.1 is concerned, it has sent a request to 101.0.0.3 on Port 90 and has received a response back from 101.0.0.3 on Port 90. But this isn’t what actually happened. The traffic never really touched 101.0.0.3. But, because of the way the packets were rewritten, 101.0.0.1 sees that it has gotten a response from 101.0.0.3.

The perceived destination is always from the perspective of the requesting computer. As you can see in the diagram: despite 101.0.0.4 becoming the real-time destination for traffic from 101.0.0.1, the destination for all traffic (as far as the requesting host knows) is 101.0.0.3.

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