Unregistered at IANA; occasionally chosen by hand as an alternate SSH port, nothing more.
IANA has no assignment for 722, and Nmap records it as "unknown". Because it sits just above the assigned block around 720 it sometimes gets picked as a hand-configured port for SSH or another admin service by people trying to move off 22. That is a local convention, not a standard, so there is no protocol you can assume from the number alone. Fingerprint whatever answers before treating it as anything in particular.
Expose with care
Moving a service to an unregistered port hides it from casual scans but not from a service scan; judge the exposure by the service you find, not the number.
$ nmap -sV -p 722 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.
Get Beige Box →also available as JSON · Markdown
Corrections or a missing port? Reply @rimrocksystems.