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:
Development of Third Generation (3G) networks
Large amounts and types of content available on the Internet, including video, voice, and images
Ever increasing number of wireless subscribers and Internet users
Development of convergent devices that offer voice and data
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.
In an Mobile IPv6 environment, nodes can have the following roles:
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.
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.
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:
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.
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.
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.
Figure 2-1 shows the following scenarios:
The mobile node on its home link. It is considered to be "at home." Packets from the correspondent node that are addressed to the mobile node's home address are delivered through standard IP routing mechanisms.
The mobile node on a foreign link. It is considered to be "away from home." The mobile node sends a Binding Update to the home agent, informing it of its care-of address. Packets from the correspondent node that are addressed to the mobile node's home address are intercepted by the home agent and tunneled to the mobile node. Upon receipt of the packet, the mobile node sends a Binding Update to the correspondent node. The correspondent node creates a binding between the home address and care-of address. It can then communicate directly with the mobile node without the need to go through the home network.
This route optimization eliminates what is commonly known as triangle routing, eliminates congestion at the mobile node's home agent and home link, and reduces the impact of any possible failure of the home agent, the home link, or intervening networks leading to or from the home link.
When the mobile node is away from home, it always sends a Home Address option to inform the receiver of its home address. That way, the receiver can correctly identify the connection to which the packet belongs.
The mobile node back on its home link. On the home link, the mobile node sends a Binding Update to the home agent and to the correspondent node to clear the bindings.
Figure 2-1: Mobile IPv6 Communications