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Networking Fundamentals · Foundational

File Transfer Protocol (FTP)

A protocol for transferring files that uses TCP port 21 for control and port 20 (active mode) or a negotiated port (passive mode) for data.

Definition

FTP sends credentials and data in clear text, so it should be replaced with SFTP or FTPS. In active mode the server connects back to the client from port 20, which firewalls and NAT often block; passive mode has the client open both connections.

Example

ftp ftp.example.com opens a control connection to TCP 21.

Exam tip

FTP = TCP 20/21, cleartext. Passive mode fixes most firewall problems.

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