FTP (File Transfer Protocol)
FTP (RFC 959) is a decades-old protocol for transferring files between a client and server, typically on port 21, whose USER and PASS commands send a login's username and password as plain, unencrypted text. AdminKit's guide checks whether a device's FTP port is actually reachable from the public internet.
By AdminKit team, Netbase JSC · Updated
FTP (RFC 959) transfers files between a client and server over two separate TCP connections: a control connection, normally on port 21, that carries commands and replies, and a second data connection — opened by either side depending on active or passive mode — that actually moves file contents. RFC 959 defines the USER and PASS commands that authenticate a login, and the RFC itself never hides that these cross the control connection as plain text; it only asks client software to hide the password on screen, not to encrypt it on the wire. FTPS wraps the same commands in TLS, and SFTP is a different protocol entirely that runs over SSH — both exist precisely because plain FTP never gained encryption of its own. A reachable, unencrypted port 21 today usually means a legacy system nobody has migrated off plain FTP.