If you want to block incoming traffic on specific ports, you can use following command − sudo iptables -A INPUT -p tcp -dport -j DROP This will set default policy for outgoing traffic to ACCEPT, which means all outgoing traffic will be allowed. To allow all outgoing traffic, enter following command − sudo iptables -P OUTPUT ACCEPT It is important to allow outgoing traffic from your server, as this is necessary for many applications and services to function properly. This will set default policy for incoming traffic to DROP, which means all traffic will be blocked except for traffic on port 22 (SSH). Sudo iptables -A INPUT -p tcp -dport ssh -j ACCEPT To implement this rule, enter following commands − sudo iptables -P INPUT DROP SSH is a secure way to access your server remotely, and it is important to allow access to it while blocking all other traffic. The first rule is to block all incoming traffic except for SSH. These rules will help you secure your network and prevent unauthorized access, while also allowing legitimate traffic to pass through. In this article, we will explore 20 useful IPtables firewall rules that every Linux administrator should know. IPtables is a powerful firewall tool that comes pre-installed on most Linux distributions. As a Linux administrator, one of most important aspects of maintaining a secure and stable network is implementation of an effective firewall.