Unassigned at IANA — no standard service owns 4998.
4998 has no entry in the IANA service name and port number registry, while its neighbours 4999 (HFSQL manager) and 5000 (commplex-main) do. Nmap's services file lists it as "maybe-veritas" with a very low hit frequency, a guess carried from old scan data rather than a confirmed protocol. Anything listening here is application-specific, so identify it by its banner rather than by the number.
Expose with care
An unregistered port tells you nothing about what is behind it. Find out what process owns the socket before deciding whether it belongs on a public interface.
$ sudo lsof -nP -iTCP:4998 -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.