The remote-console partner to VMware's 902 on older ESX and GSX/Server hosts; IANA registers it as ideafarm-panic.
Older VMware products — ESX 3.x and 4.x, GSX Server and VMware Server — carried remote console traffic on 903 alongside the authentication daemon on 902. Current vSphere consolidates console and MKS traffic onto 902 and 443, so 903 now shows up mainly on legacy hosts that were never retired. The IANA registration, ideafarm-panic, is an unrelated legacy assignment with no public specification, and nmap's service table additionally labels 903 iss-console-mgr after ISS RealSecure's console manager. Three plausible names, so identify this one by what is next to it on the host.
Do not expose
If it is the VMware console port, it is a virtual-machine console plane on a hypervisor old enough to be out of support — the worst of both problems. Keep it on a management network.
$ nc -vz -w 3 TARGET 903Seen 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.