Bala,
Don't be afraid to read. If you want to get a quick intro to computer security, and what it mean to be an Ethical Hacker, I'd suggest hacking for dummies. A new edition is due out in December. After that I'd look into some other security related books. As for your road map...
1. LAN / WAN technologies
2. Routing Basics
3. WAN routing, Internet Cloud
4. How Ethernet works
5. IP Packets in detail.
6. RFC on IP, TCP/IP, UDP
7. Working with Wireshark - Tracing Packets and understanding it
8. Firewalls - Juniper / CISCO / Linux IP Tables
9. VLAN concept
10.VPN Techniques
11.Setting up VPN
12.Tunnelling
13.packet encryption...
The way I'd do it, 1, 5 and 7 together, 4, 2 and 3 together, 6, 13, 12, 9, 10, 11. Skip 6 except for the overviews if you want, and RFC 1918 only to the point where you know what addresses are reserved.
As Awesec and Mambru have said, most of this would be covered by studying for the CCNA. Also don't expect a cert to mean you're qualified for a job.