What is FTP?

FTP (File Transfer Protocol) is an application-layer protocol used to transfer files between a client and a server over a network.

In short: FTP lets you upload files to a server and download them from it.

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#Why FTP is needed

FTP is used when you need to:

• upload files to a server (for example, a website)
• download files from a server
• manage files on a remote server (create folders, delete files, rename them)

FTP used to be the main way to work with files on servers.

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#How FTP works (simplified)

FTP uses a client-server model:

1. The FTP client connects to the FTP server
2. The client authenticates (login/password)
3. The client:

• requests a list of files
• uploads or downloads files

4. The server executes the commands and responds

People usually use dedicated programs - FTP clients.

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#FTP's quirk: two connections

This is a popular interview question.

FTP uses two communication channels:

• a control connection - for commands
• a data connection - for transferring files

Because of this, FTP can be harder to configure in networks with NAT and firewalls.

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#Active and passive FTP modes

• Active mode - the server connects to the client itself
• Passive mode - the client connects to all of the server's ports

In practice, almost everyone uses passive mode, because it works better through a firewall.

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#FTP's main drawback

FTP does not encrypt data:

• the login and password are sent as plain text
• files are transferred without protection

So in its plain form, FTP is considered insecure.

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#Secure alternatives to FTP

• FTPS - FTP + SSL/TLS
• SFTP - file transfer over SSH

Modern systems more often use SFTP rather than FTP.

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#A real-life example

FTP is like a remote file manager:

• your computer is the client
• the server is a "remote drive"
• you copy files back and forth

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#Short answer for the interview

A ready-made phrasing:

FTP is an application-layer protocol designed to transfer files between a client and a server over a network. It lets you upload, download, and manage files on a remote server, but in its basic form it does not provide data encryption.