Docker Host & check_mk agent

I have Ubuntu 16.04 host, i have installed check_mk agent on it & all was ok. Then i installed docker on it & now i can not hit port 6556 & hence check_mk checks are failing. I tried per docker KB but no luck – Add iptables policies before Docker’s rules

All of Docker’s iptables rules are added to the DOCKER chain. Do not manipulate this table manually. If you need to add rules which load before Docker’s rules, add them to the DOCKER-USER chain. These rules are loaded before any rules Docker creates automatically.

sudo iptables -I DOCKER-USER -p tcp --dport 6556 -m conntrack --ctstate     NEW,ESTABLISHED -j ACCEPT

Source: StackOverflow