The management channel of 3eTI ruggedized wireless gear — almost nothing else uses it.
IANA registered 5221/tcp in 2010 as 3exmp, the 3eTI Extensible Management Protocol for OAMP (operations, administration, maintenance, provisioning). 3e Technologies International builds hardened wireless and cybersecurity appliances for military and industrial networks, and the protocol carries device management for that equipment. UDP 5221 is reserved, not assigned. Outside a site running 3eTI hardware you will effectively never see this port open.
Do not expose
This is a device management plane; it belongs on a management VLAN, never on an internet-facing interface.
$ nc -vz -w 3 TARGET 5221Seen 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.