Enhance Linuxbox Security : Basic Iptables Firewall Configuration

If you are not familiar with Iptables, read this posts first.
http://linux-techy.blogspot.com/2010/04/enhance-linux-box-security-iptables.html
http://linux-techy.blogspot.com/2010/04/enhance-linux-box-security-iptables_30.html
http://linux-techy.blogspot.com/2010/06/enhance-linux-box-security-iptables.html
http://linux-techy.blogspot.com/2010/06/enhance-linux-box-security-iptables_27.html
http://linux-techy.blogspot.com/2010/06/enhance-linux-box-security-iptables_2179.html
http://linux-techy.blogspot.com/2010/12/enhance-linuxbox-security-know-all.html
 In this post, I have tried to build a simple & basic iptables firewall for filtering the outside traffic.  I’m going to create a simple shell script  which is independent to the topology of network. Later on we will add complexity to the file as per the need & topology.