The ITU-T X.510 wrapper protocol for secure directory operations — registered in 2019, seldom seen outside PKI and directory products.
IANA registered 9877/tcp as x510 in 2019 on behalf of ITU-T Study Group 17, referencing ITU-T X.510 / ISO/IEC 9584-11, "Protocol specifications for secure operations" in the OSI Directory series. The wrapper protocol carries authenticated and integrity-protected directory operations, and shows up in X.500-lineage directory and PKI implementations rather than general infrastructure. UDP 9877 is Reserved. On a typical network this port is empty.
Expose with care
The protocol is designed with its own authentication and integrity protection, but a directory service is still directory data. Expose it only if you have deliberately deployed X.510 and configured its trust anchors.
$ nc -vz TARGET 9877Seen 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.