The Fieldbus Message Specification port — the actual read/write messaging of FOUNDATION Fieldbus HSE.
FMS is the application-layer messaging service of FOUNDATION Fieldbus: it is how a host reads and writes the parameters of function blocks living in field devices. On HSE it is registered to the Fieldbus Foundation on port 1090, alongside annunciation on 1089 and system management on 1091. If 1090 is open, you are looking at process-control gear — a linking device, gateway, or controller — not an office server.
Do not expose
FMS is the write path into live process control. Anything that can reach it can attempt to change device parameters; isolate it on the control network.
$ nmap -sV -Pn -p 1090 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.