Registered to IBM in 2006 as a manager service, with no public specification.
IANA lists 3801 as ibm-mgr, "ibm manager service", registered by Tim Hahn of IBM in March 2006. IBM never published a protocol description tied to this port, and it is not one of the ports its current systems-management documentation tells you to open. Scanners find it open only occasionally. The registration is essentially the entire verifiable story.
Expose with care
If this really is a management agent, management planes belong on an internal network — confirm what is listening before allowing it through a firewall.
$ nmap -Pn -sV -p 3801 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.