File Transfer Protocol (FTP)

FTP operates using two TCP connections:

1. Control Connection: Used for transmitting control commands and responses. The server listens for control connection requests on port 21, which are initiated exclusively by the client.
2. Data Connection: Used for transferring files. This connection can be initiated by either the client or the server. When initiated by the server, it is referred to as Active Mode, while client-initiated connections are referred to as Passive Mode.

FTP has traditionally been utilized for tasks such as uploading web pages and associated files to web servers or distributing software and files from servers. However, due to its long history dating back to the early days of the internet, FTP is known to have security vulnerabilities. As a result, more secure alternatives have gained prevalence in recent years. For example, HTTP downloads are now widely used for distributing files and software via websites, while Content Management Systems (CMS) have become popular for updating web content.