Unregistered with no documented service; it is in Nmap's default scan set on frequency data alone.
IANA has no assignment for 17877 and Nmap carries no name for it, yet it ranks inside Nmap's default top-1000 TCP ports because scans encounter it open. No mainstream product documents it as a default listener, and nearby ports in the 17870-17890 range are unassigned as well. An open 17877 tells you a process chose that number, nothing more.
Expose with care
Unknown service, so no defensible verdict from the port alone. Version-scan it and attribute it to a process before deciding whether it should be reachable.
$ nmap -Pn -sV -p 17877 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.