as long as your iptables is saved regularly, this command is pretty useful for those IPs that just seem to linger and never go away. i have this problem with IPs in korea.
as such, i’ve implemented the following “paranoid” iptables rule which i consider pretty helpful to keep them out for good:
# iptables -t nat -I PREROUTING 1 -s 222.122.0.0/16 -j DROP
simply put, this bans the entire 222.122.x.x subnet on the NAT table and prevents any packets from coming in.