Dual network card centos7 iptables firewall and /etc/rc.d/rc.local start running

chmod a+x /etc/rc.d/rc.local
vim /etc/rc.d/rc.local
echo 1 > /proc/sys/net/ipv4/ip_forward
iptables -F
iptables -Z
iptables -X
iptables -t nat -I POSTROUTING -s Internal network number/subnet mask digits -o Egress network card dev name -j MASQUERADE