No IANA registration and no established service — an application-specific listener if you find it open.
7103 is absent from the IANA registry on both TCP and UDP; the neighbouring assignments are 7100 (X Font Service) and 7101 (Embedded Light Control Network). Nmap carries it as "unknown" with an open-frequency of 0.000304, so it is seen occasionally in wide scans but with no consistent service behind it. Treat it as an arbitrary high port chosen by whatever software is running.
Expose with care
Nothing about the number tells you the risk; identify the listening process first, then apply that service's rules.
$ sudo lsof -nP -iTCP:7103 -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.