Port

Port 21

Conventionally used by FTP. Port assignments are conventions, so confirm the actual listener before you write a rule around this number.

TCPEncrypted: No

Protocols on this port

FTP

Legacy file transfer

Security: Plaintext credentials; migrate to SFTP or FTPS

TCP · Encrypted: No

Where this port appears in the documentation

APIs

Programmatic interfaces that let systems exchange data and invoke functions across boundaries, and the main integration surface of modern IT.

Exposure guidance

Decide reachability from the identity of the caller, not from the port number. If the service on this port carries credentials or administrative control, restrict it to an administrative network, require strong authentication, and log every session that reaches it.

Nearby ports

Port 22

In the knowledge graph

Open the interactive map centred on this entity to see everything it connects to and travel outwards from there.

Explore port 21 in the knowledge graph