packets as a part of VPN

Mobile IP (MIP) is one of the most popular solutions for handling IP mobility problems at OSI Network Layer. It is a standard communications protocol that is designed to allow mobile device users to move from one network to another while maintaining a permanent IP address [23]. There are two versions of Mobile IP: Mobile IPv4 [23] and Mobile IPv6 [15], which work for IPv4 [40] and IPv6 [41] networks respectively. This chapter will first discuss the key concepts of different versions of Mobile IP and then analyse the problems faced by Mobile IP when transferring packets as a part of VPN without double tunneling. 3.1 OVERVIEW OF MIPV4 Mobile IPv4 is a protocol enhancement that allows routing of IP packets to a moving node under IPv4 networks. Only the OSI Network Layer is enhanced to handle the problems so that the upper layer softwares can be used without any modification.  The basic components of Mobile IPv4 are: (1) Mobile Node (MN): A host that changes its point of attachment from one network to another. Its IP address will change in this situation. (2) Correspondent Node (CN): A host communicating with a Mobile Node. (3) Home Agent (HA): A router on a Mobile Node's home network. It keeps a permanent IP address (Home Address) for each Mobile Node and maintains current location (Care-of Address) for the Mobile Node. It is responsible for tunneling packets to Foreign Agent when the Mobile Node is away from home, and advertising itself. (4) Foreign Agent (FA): A router on a Mobile Node's visited network which provides routing services to the Mobile Node when registered. It is responsible