Port 20 supports FTP data and ftp-data (UDP/SCTP reference coverage) across distinct transports. Review each protocol before writing firewall or monitoring policy.
Data channel used by active-mode FTP transfers.
A server opens a data connection back to an FTP client during active-mode file transfer.
Server to client
FTP sends credentials and content without encryption. Prefer SFTP or FTPS and tightly scope firewall rules.
ftp-data (UDP/SCTP reference coverage) is documented as a network service convention for port 20 over UDP + SCTP.
Use this reference entry when identifying or validating systems documented to use 20/UDP + SCTP.
Varies
Confirm the listening process and current vendor documentation before permitting traffic; a listed convention does not prove the active service or its security posture.