Install check_mk client on your guest.
# apt-get install xinetd
# wget http://mathias-kettner.de/download/check-mk-agent_1.2.4p5-2_all.deb
# dpkg -i check-mk-agent_1.2.4p5-2_all.deb
# ufw allow from <omd server IP> to any port 6556
# lsof -P -i | grep xinetd
# nc localhost 6556