1. IPTABLE
iptables -A INPUT -p tcp -m tcp --sport 80 -j ACCEPT iptables -A OUTPUT -p tcp -m tcp --dport 80 -j ACCEPT
2. Fire Wall
sudo firewall-cmd --permanent --add-port=2181/tcp firewall-cmd --reload firewall-cmd --zone=public --list-all
iptables -A INPUT -p tcp -m tcp --sport 80 -j ACCEPT iptables -A OUTPUT -p tcp -m tcp --dport 80 -j ACCEPT
sudo firewall-cmd --permanent --add-port=2181/tcp firewall-cmd --reload firewall-cmd --zone=public --list-all