Ports – the doors of network devices

What are ports?

As mentioned in the previous posts we know, what IP addresses are and how an IP network is basically built.

Lets stay with the example from “What is an IP address?” where an IP address is similar to a house address. Therefore we can make the analogy, that a port ist a special entry (door, window or something the like) of a house, which belongs to a special application.

Port numbers can range from 0 to 65535 where some of these are predefined.

  • System Ports (0 – 1023)
    • Predefined / standardized ports
  • User Ports (1024 – 49151)
    • User can define (if not already occupied by another application) their own ports for their specific application
  • Dynamic Ports (49152 – 65535)
    • This area is used primarily by the operating system for dynamically generated port assignments.

In the following screenshot you can see a section of the application “Wireshark”.
In this screenshot you can see an HTTPS request which has been sent from a clients (192.168.0.110) automatically generated port 63595 to my server (192.168.0.2) to the default HTTPS port 443.

Since all my websites are secured via HTTPS we can’t see any more human readable data (like z.b. the HTTP Protokoll) since all the data is being encrypted via TLSv1.2.

To standardize the usage of commonly used applications specific ports have been predefined.

Common standardized ports

PortProtokoll
80HTTP
443HTTPS
21FTP & FTP with explicit TLS
22SSH
110POP3
995POP3 encrypted
143IMAP
993IMAP encrypted
25SMTP
587SMTP encrypted
3306MySQL
53DNS

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