Telnet on 6556 port hanginf on host

If I try to telnet to a host on port 6556 the response remains “hanging” and does not terminate, and at the end of the chack_mk server I get a time out message.
The machine is on a network where there are no active firewalls, nor between
the host and the check_mk server. A similar machine works without problems.
Any suggestions ? Thanks.

First check - execute the check_mk_agent locally on the machine and inspect the runtime and the output.


Next: Check all firewalls on the way, including the one on the monitored system.