Unregistered, and one below Ganglia's 8649 — which is the only reason it gets noticed.
IANA has no assignment for 8648. Its neighbour 8649 is the Ganglia monitoring daemon's default port, and Ganglia deployments often spread extra channels across nearby numbers, but nothing documents 8648 specifically as a default. Nmap lists it as "unknown" at roughly 0.015% open. Read a listener here as an unidentified service that happens to sit next to a known one.
Expose with care
Do not infer Ganglia from adjacency. Identify the process, and if it does turn out to be a monitoring channel, keep it internal.
$ sudo lsof -nP -iTCP:8648 -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.