The sibling of 2045's cdfunc — same blank registration, same absence of software.
IANA registers sdfunc on TCP and UDP 2046 with no description, assignee or reference, and it appears in Unix /etc/services as a bare name for the same reason. Nothing widely deployed listens here, and Nmap's frequency table puts it near the bottom at roughly 0.02% of hosts. There is no protocol to describe because none was ever documented.
Expose with care
A listener on an undocumented port is an unknown service. Identify the process before exposing it.
$ sudo lsof -nP -iTCP:2046 -sTCP:LISTENSeen 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.