Mobile IP Description

Traditional implementations of the TCP/IP suite of protocols assume that a node’s IP address uniquely identifies its point of attachment to the Internet. In this environment, a node could maintain continuous connectivity while moving between different networks in one of two ways:

1) the mobile node could alter its IP address every time it moved, or

2) it could have host specific routes propagated to all possible correspondents throughout the Internet.

Both of these scenarios are undesirable. Altering the IP address would cause the breakdown of existing transport level connections, while the propagation of host routes causes severe scaling problems, especially with an ever-increasing number of mobile nodes seeking the host node.

Mobile IP is an Internet industry standard that enhances the IP protocol to remedy these existing problems and allows transparent routing of IP datagrams to mobile nodes on the Internet. Figure 1 shows a high-level diagram of the AirBoss Mobile IP Network Configuration.

Figure 1 - AirBoss Mobile IP Network Configuration

Using the Mobile IP solution, the mobile nodes in Figure 1 are always identified by their permanent home address, regardless of their current point of attachment to the Internet. In addition to this permanent home address, the mobile node, while away from its home network, is also associated with a temporary care-of address, which provides information about the current point of attachment to the Internet. Mobile IP makes the goal of location-transparent communications possible by defining a set of mechanisms for mobile nodes to acquire a care-of address. It also ensures a means by which packets destined for the mobile node (and hence delivered by traditional IP routing mechanisms to the mobile node’s home network) are ultimately forwarded to the present location of the mobile node, as indicated by its current care-of address.

The basic element in this protocol is the Mobile Node, also referred to as the mobile host, which roams among its home network and other foreign networks. Mobility is achieved in part by having a host on the mobile node’s home network, called the Home Agent, which is responsible for trapping packets destined to the mobile node, and then forwarding them to the present location of the mobile node, if it is away from home. The present location of the mobile node is in the form of a care-of address. This care-of address is obtained either directly by the mobile node using an external assignment mechanism (i.e., Dynamic Host Configuration Protocol [DHCP]) or from a special node, called a Foreign Agent, which is present on the foreign network and provides mobility services to visiting mobile nodes. Packets are forwarded from the Home Agent to the care-of address by encapsulating and tunneling them to the care-of address. If the care-of address at the end of the tunnel is that of the Foreign Agent, the packets are decapsulated by the Foreign Agent and forwarded by link-level mechanisms locally to the mobile node.