No IANA assignment and no established convention — an open 301 identifies nothing.
The registry has no entry for 301 on TCP or UDP; the surrounding 301–307 range is likewise blank. Nmap carries it as "unknown" with a low but non-zero open rate, which is characteristic of a port used by a handful of appliances or in-house services rather than any standard protocol. There is no banner, no RFC, and no vendor default worth naming here. Fingerprint the listener; the number will not tell you.
Expose with care
Unknown service on a privileged port — determine what it is and whether it authenticates before it goes anywhere near a public interface.
$ nmap -sV -p 301 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.
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Corrections or a missing port? Reply @rimrocksystems.