Part of IANA's reserved 1011–1020 block — held back deliberately, so no service will ever be registered here.
IANA marks the whole 1011–1020 range Reserved, which is a stronger statement than Unassigned: these numbers are held back and not handed out. No standard service exists or will exist on 1011, and nmap lists it as unknown with a very low open rate. Anything listening is a purely local decision, made by a privileged process since the port is inside the system range.
Expose with care
A reserved port with a listener on it is by definition something nonstandard running with root privileges. Identify it; there is no registry entry to fall back on.
$ sudo lsof -nP -iTCP:1011 -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.