Simple configuration of Linux firewall with insertion rules

View the current firewall Settings

iptables -L INPUT -n --line-numbers 

Delete 1 policy, such as line 4 policy

iptables -D INPUT 4

-A: insert at the tail

-I (insert) inserts a new rule in the specified chain to indicate which line to insert

(e.g., insert at line 7)

iptables -I INPUT 7 -p tcp -m state --state NEW -m tcp --dport 81 -j ACCEPT

And then save

service iptables save

And then restart

service iptables restart