Unregistered, unnamed, and near the top of the obscure-high-port frequency band.
55600 carries no IANA assignment, since RFC 6335 excludes the whole 49152-65535 range from registration. Nmap's nmap-services lists it "unknown" at 0.000760 for TCP and 0.000502 for UDP — a comparatively high figure that puts it comfortably inside the default top-1000 scan, but says nothing about what is behind it. SANS ISC records probes against it with no service name attached. That is the entire documented record.
Expose with care
A relatively high observed-open rate makes this a port scanners will try. Do not leave an unidentified service on it facing the internet.
$ nc -vz -w 3 TARGET 55600Seen 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.
Get Beige Box →also available as JSON · Markdown
Corrections or a missing port? Reply @rimrocksystems.