Env: Debian9 or Ubuntu
apt install ipset
ipset create blacklist hash:ip hashsize 4096
ipset create blacklist6 hash:net hashsize 4096 family inet6
ipset add blacklist 51.15.13.235
iptables -I INPUT -m set --match-set blacklist src -j DROP
ip6tables -I INPUT -m set --match-set blacklist6 src -j DROP
ipset list
iptables -L -nv