setup NAT with iptable on linux based machines

First delete existing iptables table rules then execute 

the following commands....

iptables -F

iptables -t nat -F

iptables -t mangle -F

Enable NAT using this command 

iptables -t nat -A POSTROUTING -o eth0 -j 

MASQUERADE

iptables -A FORWARD -i eth1 -j ACCEPT