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

To block specific port number such tcp port # 5050, enter:

iptables -A OUTPUT -p tcp --dport 5050 -j DROP

To block tcp port # 5050 for an IP address 192.168.1.2 only, enter:

iptables -A OUTPUT -p tcp -d 192.168.1.2 --dport 5050 -j DROP

For unblock just change -A to -D on the above command