Kerberized rlogin — the r-services with Kerberos tickets instead of .rhosts trust.
TCP 543 is registered as "klogin": rlogin authenticated with Kerberos, so the client presents a ticket rather than relying on host-based .rhosts files, and the session can optionally be encrypted. It was part of the Kerberos-patched application suite that shipped with MIT krb5 and with commercial Unix. MIT split those applications out of the core krb5 distribution in release 1.8 to be maintained separately, and SSH with GSSAPI has taken over the job, so a listener on 543 today means a very old Kerberos realm or an appliance that never updated.
Do not expose
An unmaintained interactive login service; even when the Kerberos authentication holds, the deployment around it is a decade or more past support. Use SSH.
$ nc -vz -w 3 TARGET 543Seen 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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