How to open check_mk port to specific IP address on CentOS 8

I installed the latest check_mk agent on a CentOS 8 server.

dnf install check-mk-agent-2.0.0p13-1.noarch.rpm

To open check_mk port to specific IP address ( for example: 10.10.10.10 is my check_mk host server ) on CentOS 8 server.

firewall-cmd --permanent --zone=public --add-rich-rule='
  rule family="ipv4"
  source address="10.10.10.10/32"
  port protocol="tcp" port="6556" accept'

Always reload firewalld after changes

firewall-cmd --reload

Disable CentOS 7 Firewalld replace by iptables

CentOS/RHEL 7 came with the new firewall called Firewalld.

It is bit complicated for me, as I am using iptables firewall from many years. The best part: all Linux came with it and you can use same scrip everywhere.

1. First Disalbe Firewalld



systemctl stop firewalld
systemctl disable firewalld



2. Uninstall it if you are more comfort with iptables



yum erase firewalld



3. Install iptables service



yum install iptables-services



4. Enable it in systemd



systemctl start iptables
systemctl enable iptables



5. Apply some basic rules



iptables -F
iptables -X
iptables -P INPUT DROP
iptables -P OUTPUT DROP
iptables -P FORWARD DROP

# Accept packets from trusted IP addresses
iptables -A INPUT -s [MY_IP] -j ACCEPT
iptables -A OUTPUT -d [MY_IP] -j ACCEPT

# Accept local nic
iptables -A INPUT -i lo -j ACCEPT
iptables -A OUTPUT -o lo -j ACCEPT

# Accept port 80
iptables -A INPUT -m tcp -p tcp --dport 80 -j ACCEPT
iptables -A OUTPUT -m tcp -p tcp --sport 80 -j ACCEPT

# Allow full outgoing connection but no incomming stuff
iptables -A OUTPUT -o eth0 -m state --state NEW,ESTABLISHED,RELATED -j ACCEPT
iptables -A INPUT -i eth0 -m state --state ESTABLISHED,RELATED -j ACCEPT



6. Save changes

Please notice the old "service iptables save" does not work anymore.
Please use this command to save the changes:


iptables-save > /etc/sysconfig/iptables