Mastering Linux Security and Hardening - Second Edition

Looking at iptables rules in RHEL/CentOS 7 firewalld

RHEL 7 and its offspring use the iptables engine as the firewalld backend. You can't create rules with the normal iptables commands. However, every time you create a rule with a firewall-cmd command, the iptables backend creates the appropriate iptables rule and inserts it into its proper place. You can view the active rules with iptables -L. Here's the first part of a very long output:

[donnie@localhost ~]$ sudo iptables -LChain INPUT (policy ACCEPT)target     prot opt source               destination         ACCEPT     all  --  anywhere             anywhere             ctstate RELATED,ESTABLISHEDACCEPT     all  --  anywhere             anywhere            INPUT_direct  all  --  anywhere             anywhere            INPUT_ZONES_SOURCE  all  --  anywhere             anywhere            INPUT_ZONES all -- anywhere anywhere ...