Block IP:
# iptables -A INPUT -s 88.89.28.110 -j DROP
or
# iptables -A INPUT -s 88.89.28.110 -j REJECT --reject-with icmp-host-prohibited

Unblock IP:
# iptables -D INPUT -s 88.89.28.110 -j DROP
or
# iptables -D INPUT -s 88.89.28.110 -j REJECT --reject-with icmp-host-prohibited

# iptables-save

List iptables rules:
# iptables -S
or
# iptables -L

iptables -t nat -A PREROUTING -p tcp --dport 80 -s 192.168.10.51 -j DNAT --to-destination 192.168.10.137:1080
iptables -t nat -A PREROUTING -p tcp --dport 80 -s 46.212.0.246 -j DNAT --to-destination 192.168.10.137:1080

88.91.120.90
46.212.0.246

88.89.28.110