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Table Of Contents  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)

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Mobile IP Overview, History and Motivation
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2
3
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Mobile IP Addressing: Home and "Care-Of" Addresses
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Mobile IP Concepts and General Operation
(Page 2 of 3)

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.

Key Concept: Mobile IP operates by setting up the TCP/IP equivalent of a mail forwarding system. A router on a mobile node’s home network serves as the mobile device’s home agent, and one on its current network acts as the foreign agent. The home agent receives datagrams destined for the mobile’s normal IP address and forwards them to the mobile node’s current location, either directly or by sending to the foreign agent. The home agent and foreign agent are also responsible for various communication and setup activities that are required for Mobile IP to work.



Previous Topic/Section
Mobile IP Overview, History and Motivation
Previous Page
Pages in Current Topic/Section
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2
3
Next Page
Mobile IP Addressing: Home and "Care-Of" Addresses
Next Topic/Section

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Version 3.0 - Version Date: September 20, 2005

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