What category do ports 0 through 1023 belong to?

Ports 0 through 1023 are known as "well-known ports." This category is reserved for system or well-known services and is defined by the Internet Assigned Numbers Authority (IANA). These ports are typically associated with widely used protocols and services, which allows applications and users to connect without needing to specify the port number in many cases.

Common examples include port 80 for HTTP, port 443 for HTTPS, and port 25 for SMTP. These assignments facilitate standardized communication across different systems and applications, ensuring that they can reliably connect to the services they expect.

The other categories, such as user ports (which range from 1024 to 49151), private ports (also known as registered ports which fall within the same range), and dynamic ports (often referred to as ephemeral ports, which are used for temporary or short-lived communication), do not encompass the full range of ports from 0 to 1023, making "well-known ports" the correct classification for this range.