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81 lines
3.0 KiB
Markdown
81 lines
3.0 KiB
Markdown
# Port Forwarding how to
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You want to open something on your network to the world.
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# What is a port
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Ports solves the problem on how to make many applications communicate over
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the network simultaneously.
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A port is a number between 0 - 65,535 that gets assigned to any application that wants
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to communicate over the network. This number is then added to every packet
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that is transmitted by that application. The system knows that any respone
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packets with that port number are to be send to that one application.
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# How firewall works
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A firewall knows direction and state of traffic.
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* It allows outgoing communication on any port.
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* But the incoming traffic gets dropped on all ports, unless it is a response
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to communication initialized from the inside.
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<details>
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<summary><b>More details</b></summary>
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* When you visit some website you initialize the communication.
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* Your browser picks a random port as the **source port** and sends a request at some IP
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using a well known https port 443 - the **destination port**
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* Then the browser is waiting for a response at that random port.
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* This traffic goes through your firewall and all that info is kept in its state table.
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* This allows firewall to know that when packets start coming from that IP, with that
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source port number now being a destination port, it is a response and let it through.
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</details>
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# Port forwarding
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What if you want to host something, lets say a minecraft server.<br>
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You set it all up, you have your IP address known to others and they try to connect,
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but your firewall blocks them. Its a connection initialized from the outside.
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So you need to tell your router/firewall to let through traffic that comes to
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minecraft default port - `25565` and where to send it on your LAN,
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to the local IP of your minecraft server.
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### Examples of port forward rule
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How to actually create that port forward rule depends on router/firewall model.
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It can be easy, it can be bit complicated.
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Generally what to expect
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* would be called port forwarding or a virtual server
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* **IP address** is a core information, it is your LAN side machine IP on which
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your stuff runs.
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* Another essential is **the port** on which to expect traffic,
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sometimes called a service port or an external port
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* it might offer option for **internal port**, this can be often left empty
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if port on which your stuff on server is running is the same as the one you
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are opening to the world. But this gives you option to open port 3333 of firewall
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but on your LAN machine have port 80 actually being used.
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* **protocol** - TCP or UDP, if dunno **select both / all**, its safer for the initial setup and testing
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# Testing if it works
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### Windows
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There are sites that will test if your port is open, but you need to run
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some service at that port.
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* [Port Listener](https://www.rjlsoftware.com/software/utility/portlistener/)
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* [yougetsignal.com](https://www.yougetsignal.com/tools/open-ports/) or
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[portchecker.co](https://portchecker.co/) or
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### Linux
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* netcat
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