Ports

Time to move up the TCP/IP Model to Layer 4 – Application.

The Internet is made of applications – web servers, email servers, storage servers, etc, and each of those applications connects to other systems with a TCP PORT. The TCP port numbers are pretty standard for normal traffic:

So you see, when you connect to a web page (HTTP or HTTPS), you either hit port 80 or 443. If you see a lock next to your browser, you’re using port 443, or HTTPS. All modern operation systems and applications (as Edge or Frirefox is an application) know these ports and connect to them automatically.

You will need to know the basics, but what if you wanted to host your own web servers from your house? That’s where the PAT (Port address translation) comes in. On your modem interface, you should see a port forwarding or NAT section:

As the help on the side states, it allows your modem, when it receives a packet on a specific port, you forward it internally for things like Xbox live, web servers, etc. You tell the modem was port (service) to use, and it will allow traffic to your internal server. Let see what that looks like for a web server:

This will take any newly incoming packets on port 80 and forward then to the device listed. Now, you’ll need something listening on that device, meaning you’ll need a web server (IIS or Apache or TinyHTTP). This comes in handy, but beware, it exposes the unpatched security flaws in that web server – and there are bots on the internet looking for unpatched web servers to turn them into bot farms.

Finally, the ports list showed TCP and UDP ports – here’s the difference. The TCP standard employs a verification or ACKnowledgement of the packet being received and the connection is viable. This ensures that the communication is correct. UDP, or user datagram protocol, isn’t worried about connection handshakes or verification – its advantage is speed, but on a bad connection, the transfer of data will not be received intact. UDP’s most common use in IT for TFTP. I’ll cover that next.