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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)

Internet Protocol Mobility Support (Mobile IP) 1 2 3 4 Mobile IP Concepts and General Operation

A Better Solution: Mobile IP

The solution to these difficulties was to define a new protocol especially to support mobile devices, which adds to the original Internet Protocol. This protocol, called IP Mobility Support for IPv4, was first defined in RFC 2002, updated in RFC 3220, and is now described in RFC 3344. The formal name as given in that document title is rather long; the technology is more commonly called Mobile IP both in the RFC itself and by networking people.

To ensure its success, Mobile IP's designers had to meet a number of important goals. The resulting protocol has these key attributes and features:

• Seamless Device Mobility Using Existing Device Address: Mobile devices can change their physical network attachment method and location while continuing to use their existing IP address.
  
  
• No New Addressing or Routing Requirements: The overall scheme for addressing and routing as in regular IP is maintained. IP addresses are still assigned in the conventional way, by the owner of each device. No new routing requirements are placed on the internetwork, such as host-specific routes.
  
  
• Interoperability: Mobile IP devices can still send to and receive from existing IP devices that do not know how Mobile IP works, and vice-versa.
  
  
• Layer Transparency: The changes made by Mobile IP are confined to the network layer. Transport layer and higher layer protocols and applications are able to function as in regular IPv4, and existing connections can even be maintained across a move.
  
  
• Limited Hardware Changes: Changes are required to the software in the mobile device, as well as to routers used directly by the mobile device. Other devices, however, do not need changes, including routers between the ones on the home and visited networks.
  
  
• Scalability: Mobile IP allows a device to change from any network to any other, and supports this for an arbitrary number of devices. The scope of the connection change can be global; you could detach a notebook from an office in London and move it to Australia or Brazil, for example, and it will work the same as if you took it to the office next door.
  
  
• Security: Mobile IP works by redirecting messages, and includes authentication procedures to prevent an unauthorized device from causing problems.

Mobile IP accomplishes these goals by implementing a forwarding system for mobile devices. When a mobile unit is on its “home” network, it functions normally. When it moves to a different network, datagrams are sent from its home network to its new location. This allows normal hosts and routers that don't know about Mobile IP to continue to operate as if the mobile device had not moved. Special support services are required to implement Mobile IP, to allow activities such as letting a mobile device determine where it is, telling the home network where to forward messages and more. I explore Mobile IP operation more in the next topic, and the implementation specifics in the rest of this section.

Mobile IP is often associated with wireless networks, since devices using WLAN technology can move so easily from one network to another. However, it wasn't designed specifically for wireless. It can be equally useful for moving from an Ethernet network in one building to a network in another building, city or country. Mobile IP can be of great benefit in numerous applications, including traveling salespeople, consultants who visit client sites, administrators that walk around a campus troubleshooting problems, and much more.

Internet Protocol Mobility Support (Mobile IP) 1 2 3 4 Mobile IP Concepts and General Operation