FTP and SSH

FTP uses separate control (21) and data channels — active mode opens inbound data connections; passive mode has the server pick a high port. SFTP is not FTP over SSH — it is SSH subsystem for file transfer. SCP is simpler one-way copy over SSH.

FTP modes

Mode	Who connects data	Firewall note
Active	Server connects to client data port	Client must allow inbound — painful
Passive	Client connects to server high port	Open outbound + server port range
FTPS	TLS on FTP	Explicit vs implicit TLS — different ports
SFTP	Single SSH session	Only 22/tcp — easier to policy

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