The IS-IS daemon's command line on an FRR router.
FRRouting defines 2608 as ISISD_VTY_PORT, the telnet-style CLI for isisd, in the same series as ospfd (2604) and bgpd (2605). A listener here means a box is running IS-IS under FRR, which in practice means a data-center fabric or a service-provider core built on Linux routing. IANA registers 2608 to "Wag Service", an assignment you will not meet in the wild.
Do not expose
Same problem as every FRR vty port: cleartext telnet into a routing daemon's configuration — keep it on loopback.
$ nc -v -w 3 TARGET 2608Seen 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.