2    What is Mobile IPv6?

In communications the trend is to mobility. Mobile telephones have already transformed business and personal interactions. Computers, especially laptop computers and handhelds, are also mobile, but they currently do not enjoy the continuous connectivity that the mobile telephones have.

Today, there are very basic data services that use the Wireless Application Protocol (WAP) and General Packet Radio Service (GPRS). But the demand for full voice and data mobile communications is being driven by the following trends:

The Internet Protocol Version 6 (IPv6) was designed to support mobility through features like its extensible header structure, address autoconfiguration, security (IPsec), and tunneling. Mobile IPv6 builds upon these features and defines operations that enable a mobile node to move from one link to another without changing the node's IP address. In this way, packets can be routed to and from mobile nodes transparently when they are on another network.

This chapter describes the Mobile IPv6 environment and how the various nodes interoperate.

2.1    Mobile IPv6 Environment

In an Mobile IPv6 environment, nodes can have the following roles:

mobile node

An IPv6 node, host or router, that can change its point of attachment from one link to another, while still being reachable through its home address.

correspondent node

A peer IPv6 node with which a mobile node communicates. The correspondent node, host or router, can be either mobile or stationary. The Tru64 UNIX implementation of Mobile IPv6 enables a system to be a correspondent node.

home agent

A router on a mobile node's home link with which the mobile node registers its current care-of address. The Tru64 UNIX implementation of Mobile IPv6 enables a system to be a home agent.

To completely understand the relationship among these nodes, you should be familiar with the following terms:

home address

The IPv6 address of the mobile node when it is on its home link, or "at home." The subnet prefix of this address is the home network's subnet prefix. The mobile node is always addressable by its home address; it does not change.

care-of address

The IPv6 address of the mobile node when it is on a foreign link, or "away from home." The subnet prefix of this address is the foreign network's subnet prefix. A mobile node can have multiple care-of addresses, but the care-of address registered with the mobile node's home agent is called its primary care-of address.

binding

An association of the mobile node's home address with its care-of address. This association also has a lifetime. Each node maintains a cache of all bindings. See Section 5.2 for information on viewing the contents of the binding cache.

2.2    How Does it Work?

Figure 2-1 shows the following scenarios:

Figure 2-1:  Mobile IPv6 Communications

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