To add an exception to firewall
In RedHat/CentOS 6
iptables --line -vnL
iptables -A INPUT -p tcp --dport 80 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A INPUT -p tcp -s 192.168.0.0/16 -j ACCEPT
iptables -D INPUT -p tcp -s 192.168.0.0/16 -j ACCEPT
service iptables save
In RedHat/CentOS 7
firewall-cmd --list-all
firewall-cmd --permanent --add-port=80/tcp
firewall-cmd --permanent --zone=public --add-source=192.168.0.0/16
firewall-cmd --permanent --zone=public --remove-source=192.168.0.0/16
firewall-cmd --reload
systemctl disable firewalld