Thank  you  for  your  information

Dear Bipin,

My suggestion is first you go through the concept of port knocking by referring this site:

http://www.portknocking.org/

After that you make two virtual machine on your system and without installing firewall, you try to port knock from one system to another system.

By using snort or wireshark you capture the packets and analysis them. Using in this way you can prevent any king of  attack.

Thank  you  for  sharing   your  knowledge.....

 One of my undergraduate students did a project that consisted of the following:

A multi threaded port knocker which used the following measures:

1) each message was sent with an RSA key for validation

2) the user used the key to encrypt the AES key

3) the AES key was used to encode the next port knocking sequence. this would protect the protocol from replay attacks.

One feature that was otu of scope but could serve as future work is cycling the AES key and RSA keys.

Hope this helps