hey i still work on my thesis and this time i determined mobile IPv6. I have some questions other than these: 1- Perhaps this is a dumb one, though i wanna ask a question first you have never heard. you know "the data encapsulation process". By doing this , can't we hide the information(data and control info)in packet from outer threats? And so , why do we "also" use IPSec protocol to hide the information if data encapsulation process already perform that? 2- There are two things: IPv4 Options and IPv6 Extension headers IPv4 Options removed since it was infrequently used. Then it has been moved to extension headers. Now let's come to question, IPv4 Options would provide us some security, also IPv4 protocol field do this by adding AH header and ESP header if IPSec is implemented. So, wasn't "AH header and ESP header" enough to provide IPSec features? why also use some information " in IPv4 Options? "