The TCP/IP Guide  9  TCP/IP Lower-Layer (Interface, Internet and Transport) Protocols (OSI Layers 2, 3 and 4)       9  TCP/IP Internet Layer (OSI Network Layer) Protocols            9  Internet Protocol (IP/IPv4, IPng/IPv6) and IP-Related Protocols (IP NAT, IPSec, Mobile IP)                 9  Internet Protocol Mobility Support (Mobile IP)

Mobile IP Overview, History and Motivation 1 2 3 Mobile IP Addressing: Home and "Care-Of" Addresses

Mobile IP Device Roles

As you can see, just as mail forwarding requires support from one or more post offices, Mobile IP requires the help of two routers. In fact, special names are given to the three main players that implement the protocol (also shown in Figure 128):

• Mobile Node: This is the mobile device, the one moving around the internetwork.
  
  
• Home Agent: This is a router on the home network that is responsible for catching datagrams intended for the mobile node and forwarding them to it when it is traveling. It also implements other support functions necessary to run the protocol.
  
  
• Foreign Agent: This is a router on the network to which the mobile node is currently attached. It serves as a “home away from home” for the mobile node, normally acting as its default router as well as implementing Mobile IP functions. Depending on the mode of operation, it may receive forwarded datagrams from the home agent and forward them to the mobile node. It also supports the sharing of mobility information to make Mobile IP operate. The foreign agent may not be required in some Mobile IP implementations but is usually considered part of how the protocol operates.

Mobile IP Overview, History and Motivation 1 2 3 Mobile IP Addressing: Home and "Care-Of" Addresses