Unassigned in the IANA registry, with no protocol or product convention behind it.
There is no IANA entry for 340 on either transport; the block from 334 through 343 is empty. Nmap records it as "unknown" on both TCP and UDP with a small open rate, meaning some hosts do answer but no consistent service explains them. Nothing about the number implies a protocol, an encoding, or an authentication model. Probe the listener and identify it on its own evidence.
Expose with care
Unregistered and unidentified — nothing here justifies internet exposure until you know what process is bound to it.
$ nmap -sV -p 340 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.
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Corrections or a missing port? Reply @rimrocksystems.