The OSPF daemon's command line on a Linux router — one vty port per routing daemon.
FRRouting (and Quagga before it) gives every routing daemon its own telnet-style vty port: zebra 2601, ripd 2602, ripngd 2603, ospfd 2604, bgpd 2605. Connecting to 2604 lands on ospfd's password prompt and, past it, the same CLI that vtysh drives locally. You meet it on Linux routers and on appliances built on FRR — Cumulus Linux, SONiC, VyOS, OPNsense/pfSense with the FRR package. IANA registers 2604 to "NSC CCS", which has nothing to do with routing.
Do not expose
A cleartext telnet admin CLI for a routing daemon, protected only by a config-file password — bind it to 127.0.0.1 and reach it through vtysh or SSH.
$ nc -v -w 3 TARGET 2604Seen 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.