This book explores advanced IPSec algorithms and protocols for IP version 4 communications from a practical point of view. The architecture of the IPSec protocol framework is discussed and a detailed critical evaluation of component protocols such as Authentication Header (AH), Encapsulating Security Payload (ESP) and Internet Key Exchange (IKE) is provided. The various encryption and integrity-checking mechanisms used by IPSec are evaluated. A detailed packet-by-packet analysis of IKE protocol transactions in IPSec is also provided. A practical implementation using Cisco IOS router platform evaluates how the various IPSec protocols and standards could be combined to create a robust and functional Virtual Private Network (VPN). Various command line tools within the Cisco IOS are used to test and decompose the configuration to provide an in-depth analysis of the role of individual component protocols. Various Internet drafts and Requests for Comments (RFCs) from the Internet Engineering Task Force (IETF) are evaluated to identify the major limitations in the IPSec standard.