FTP's unprivileged twin — where an FTP server or FTP proxy lands when it cannot bind port 21.
IANA registers 2121 as SCIENTIA-SSDB, but that is not what runs there. In practice 2121 is the conventional alternate FTP port: it is above 1024, so a daemon can bind it without root, and it is where FTP proxies land — Nmap names the port ccproxy-ftp after CCProxy's FTP proxy service. It is common enough to matter, open on roughly 0.6% of scanned hosts, well ahead of everything around it. A connection returns a normal FTP banner, and the protocol is RFC 959 FTP with all of its properties intact.
Expose with care
Same rules as port 21: cleartext credentials unless the session negotiates AUTH TLS (RFC 4217), and an open FTP proxy here can be abused to relay traffic. Moving FTP off 21 hides it from nobody.
$ printf 'QUIT\r\n' | nc -v TARGET 2121Seen this on your network? Beige Box scans your Wi-Fi and shows every open port on every device — and its Ports tool links straight back here.
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Corrections or a missing port? Reply @rimrocksystems.