IPtables

iptables -L --line-numbers
# Delete rules number 3 in the list
iptables -D 3

Forward packet between vpn client subnet

iptables -A FORWARD -s 10.50.30.0/24 -d 10.50.30.0/24 -j ACCEPT

Block dst IP

iptables -A OUTPUT -d 203.151.31.76 -j DROP

Unblock dst IP

iptables -D OUTPUT -d 203.151.31.76 -j DROP