The FirewallBackend option selects the firewall backend implementation. Choices are: - nftables (default) - iptables (iptables, ip6tables, ebtables and ipset) IPTables are deprecated.
Solution
Edit the file /etc/firewalld/firewalld.conf and add or modify the following line: FirewallBackend=nftables Impact: Verifying the proper backend configuration insures the critical functionality of the firewall.