Registered as "Socalia service mux"; scanners still print the dead Chili!Soft ASP name admd.
IANA's current entry for 5100 is socalia, a service multiplexer registration with no public specification. Nmap's list carries the older label admd, the administration port of Chili!Soft ASP, a product discontinued long ago, and notes Yahoo pager traffic as another historical squatter. None of those are live software today, so treat 5100 as an unclaimed number in the 5100-5102 block and fingerprint whatever answers.
Expose with care
No standard service means no default security posture. Find the owning process before allowing it through a firewall.
$ sudo lsof -nP -iTCP:5100 -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.