If you have a prior experience with iptables and want to combine you knowledge of iptables with the features in firewalld, direct rules are here to help with this migration. Firstly, if we want to implement a rule on the INPUT chain, we can check the current settings with the following command:

# firewall-cmd --direct --get-rules ipv4 filter INPUT

If you have not added any rules, the output will be empty. We will add a new rule and use a priority of 0. This means that it will be listed at the top of the chain; however, this means little when no other rules are in place. We do need to verify that rules are added in the correct order to process if other rules are implemented:

# firewall-cmd --permanent --direct --add-rule ipv4 filter \
INPUT 0 -p tcp --dport 3128 -j ACCEPT
# firewall-cmd --reload