Centos – NAT doesnt work on CentOS 7(Firewalld)

I have configured nat to make my CentOS 7 into a router. I have used firewalld to do this. But unfortunately it doesnt work. I have no idea which causes the issue. I tried the same configuration in Virtual Box and it is working. If I did the same config in the production server it doesnt.

Eth0
ip– my static ip

mask-255.255.252.0

gateway-my ISP gateway

eth1

ip-192.168.1.30

mask-255.255.255.0

1) Enabled packet forwarding

vi /etc/sysctl.conf

added “net.ipv4.ip_forward=1”

sysctl –p 

2) Configuring the NAT in firewalld

i) Integrating the interface “eth1” to the internal zone

Firewall-cmd --change-interface=eth1 --zone=internal --permanent

• Masquerading was “off” in default

ii) Integrating the interface “eth0” to the external zone

Firewall-cmd --change-interface=eth0 --zone=external --permanent

iii) Changed “internal zone” as the default zone

Firewall-cmd --set-default-sone=internal --permanent

iv) Added DNS to pass through “internal zone”

Firewall-cmd --zone=internal --add-service=dns –-permanent

3) Saved the firewall configuration

Firewall-cmd --reload

Firewall-cmd --complete-reload

4) Also tried in the iptables

Iptables –t nat –A POSTROUTING –o eth0 –j MASQUERADE

Iptables –A FORWARD –i eth1 –j ACCEPT

Echo > 1 /proc/sysc/net/ipv4/ip_forward

Service iptables restart