Hi jimp,
Thanks for the ultrafast reply :-)
Yes indeed, it's the check_mk package. We're monitoring with it the firewalls and then we have all 5 minutes a login to the firewall via ssh from the monitoring host.
I know check_mk can be used over a tcp-port but our development here decided to use it strictly over ssh, even when problems like this arise. (Which I don't understand why over ssh).
On my private installation I'm using Zabbix as the monitoring, much more advanced, also encrypted direct agent/proxy communication and also great it is supported as a package by pfSense ;-)
No problems with the Zabbix Agent there.