Registered as "isis" — and it is not the IS-IS routing protocol.
IANA registers the name isis on TCP and UDP 2042, with isis-bcast next door on 2043; the entry carries no description or reference document. The obvious guess is wrong: the IS-IS routing protocol (ISO 10589, extended for IP by RFC 1195) runs directly over the data link layer and has no TCP or UDP port at all, so nothing you see on 2042 is IS-IS. Nmap finds the port open on about 0.02% of scanned hosts, and no common software claims it.
Expose with care
The name misleads. Identify the actual listener rather than assuming a routing daemon, and expose it only once you know what it is.
$ sudo lsof -nP -iTCP:2042 -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.