Assuming you want to NAT the network on eth1 and route the traffic to eth0 this is the spell:
Create the forwarding rule:
/sbin/iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
and then enable IP forwarding
echo “1” > /proc/sys/net/ipv4/ip_forward
OR
sysctl -w net.ipv4.ip_forward=1
Permanent setting using /etc/sysctl.conf
If we want to make this configuration permanent the best way to do it is using the file/etc/sysctl.conf where we can add a line containing net.ipv4.ip_forward = 1
/etc/sysctl.conf: net.ipv4.ip_forward = 1
if you already have an entry net.ipv4.ip_forward with the value 0 you can change that 1.
To enable the changes made in sysctl.conf you will need to run the command:
sysctl -p /etc/sysctl.conf
On RedHat based systems this is also enabled when restarting the network service:
service network restart