Uncomplicated Firewall (ufw) is one of the greatest frontends to iptables I’ve encountered. It is very simple to use, and I just wish it were also available for Gentoo. Up until recently, everything went smoothly for me and ufw, but we hit some rough waters when I tried to block an IP range.
To block an IP or IP range in ufw, you should do
sudo ufw deny from 188.162.67.197/21