A number of methods have evolved over the years to address the need for
security. Most of these are focused at the higher layers of the OSI protocol stack in
order to compensate for IP’s lack of security. These solutions are valuable for certain
situations, but they can’t be generalized easily because they are particular to various
applications. For example, we can use Secure Sockets Layer (SSL) for certain applications
like World Wide Web access or File Transfer Protocol (FTP), but there are
dozens of applications that this type of security was never intended to work with