DD-WRT :: View topic - Understanding Port Forwarding, UPnP, and why/when needed? (2024)

It's from 2003 and comes with all of the trappings of 2003 online multiplayer.
One common theme is an inability to connect between players, and the common answer is always: "Enable Port Forwarding to a Static IP Address".

This has been a common theme for old computer games, and even new computer games or programs with connectivity issues have port forwarding as a troubleshooting step.

Thing is I now have neither port forwarding nor UPnP enabled and it works.
Additionally, how is port forwarding handled if you have multiple computers needing the same ports? If I forward sftp port 22 to one computer, I can still connect via sftp from other computers... in practice.

This all seems a bit voodoo and voodoo doesn't exist in computer science/engineering, even if people now try with AI.... and AI isn't playing a role here.

A Port Number on a computer is like a particular runway (say R) of an airfield. And runway R is DESIGNATED for a specific plane (say P), by prior agreement, between airfield administration and airplane pilots. When P is using R, no other plane can use runway R due to potential clashing.

While an airfield may have a few runways (physical constraints), a computer has plenty of ports. It's 65,535 port (numbers) although not all are free for discretionary use. For example, port 80 is for http, 443 for https, 20 & 21 are for FTP.

Roughly, this is how computer ports work. See the linked article for further info.
https://www.cloudflare.com/learning/network-layer/what-is-a-computer-port/

Deciphering my metaphor. Airplanes are apps, airfield is your PC and you're the administrator who is asking questions.

Good luck.

I really like that analogy... What if I have two devices on the network who both want to use port 22 for FTP transfers for example?

This way, the router knows which PC a packet is coming from/to (using Layer 3). A switch uses MAC addresses (Layer 2).

This is essentially where the Open Systems Interconnection (OSI) kinda takes over. I'd suggest have a good read on OSI.

Good luck.

(edited for clarity)

Last edited by D.F.Cruizer on Fri Aug 30, 2024 19:03; edited 1 time in total