If you have multiple ethernet NICs that you want to apply all rules to, then
you can set
ETH6_DEVICE (for ipv6) in
/etc/csf/csf.conf to the interface name immediately
followed by a plus sign. For example, eth+ will apply all iptables rules to eth0, eth1, etc.
If you leave
ETH_DEVICEblank all rules will be applied to all ethernet devices equally.