Login as root (su)
Check that iptables is installed (should be by default)
iptables -V
To block his IP range type:
iptables -A INPUT -s 193.95.228.0/24 -j DROP
However you can make it so when he connects he will connect to himself which is hilarious.
iptables -A INPUT -s 193.95.228.0/24 -j MIRROR