Unassigned at IANA — nothing standard claims it.
IANA lists the whole 6559-6565 block as Unassigned, and nmap's service database has no name for 6565 either. There is no registered protocol, no well-known product default, and no notable malware association documented for it. An open 6565 is an application that picked a free high port, so the only way to know what it is, is to look on the host.
Expose with care
Unassigned does not mean harmless — whatever bound it is unidentified, so treat it as unknown software until you name the process.
$ sudo lsof -nP -iTCP:6565 -sTCP:LISTENSeen 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.