Another unassigned port in the 250–255 gap, with no protocol behind the number.
IANA lists no assignment for 255 on either transport, and there is no historical registration to point at. Like its neighbour 254 it still carries a measurable open-rate in Nmap's frequency data, so it rides along in default scans and turns up in results as a nameless open port. Any listener is site-specific: an internal service someone parked on a low, memorable number, or a device firmware default that was never registered. There is nothing generic to say about what it does.
Expose with care
Unregistered does not mean harmless — fingerprint the listener before exposing it, because low-numbered ports usually mean a root-owned process.
$ nmap -sV -p 255 TARGETSeen 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.