Master Linux Firewall: firewalld and iptables Commands Explained

firewalld (CentOS 7+)

Start the firewall service systemctl start firewalld Stop the firewall service systemctl stop firewalld Check firewall status systemctl status firewalld Enable firewall at boot systemctl enable firewalld Disable firewall at boot systemctl disable firewalld Reload firewall rules firewall-cmd --reload Open a port (requires reload to take effect)

firewall-cmd --zone=public --add-port=8080/tcp --permanent

List opened ports firewall-cmd --list-ports Close a port

firewall-cmd --zone=public --remove-port=8080/tcp --permanent

iptables (CentOS < 7)

Installation

Install iptables package yum install iptables Install iptables services

yum install iptables-services

Service Control

Start iptables systemctl start iptables.service Stop iptables systemctl stop iptables.service Check iptables status systemctl status iptables.service Enable iptables at boot systemctl enable iptables.service Disable iptables at boot

systemctl disable iptables.service

Rule Management

View filter table chains (e.g., INPUT) iptables -L -n View NAT table chains iptables -t nat -L -n Flush all rules

iptables -F

iptables -X

iptables -Z

Add rule to open port 8080 on INPUT chain iptables -I INPUT -p tcp --dport 8080 -j ACCEPT List rule line numbers for INPUT chain iptables -L INPUT --line-numbers -n Delete rule by line number (e.g., close port 8080)

iptables -D INPUT 1