Unregistered and undocumented — present in default scans purely on frequency data.
18988 has no IANA assignment and no Nmap service name. It sits in Nmap's default top-1000 TCP list because internet-wide scanning found it open often enough to be worth including. There is no known product default behind it, so any description of an open 18988 has to come from probing the host, not from a registry.
Expose with care
Unknown listener. Attribute it locally, then apply the verdict its actual protocol deserves.
$ nmap -Pn -sV -p 18988 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.