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Mobile IP (MIP) is an IETF (Internet Engineering Task Force) standard communications protocol designed to allow users of mobile devices such as laptops, PDAs and mobile phones to move from one network to another while maintaining their permanent IP address.

Defined in RFC (Request for Comments) 2002, mobile IP is an enhancement of the internet protocol (IP) that adds mechanisms for forwarding internet traffic to mobile devices known as mobile nodes when they are connecting through other than their home network.

Mobile IP works something like this:

Mobile IP enables routing of IP datagrams to mobile nodes. The mobile node’s home address always identifies the mobile node, regardless of its current point of attachment to the internet or an organization’s network.

When away from home, a care-of address associates the mobile node with its home address by providing information about the mobile node’s current point of attachment to the internet or an organization’s network. Mobile IP uses a registration mechanism to register the care-of address with a home agent.

The home agent redirects datagrams from the home network to the care-of address by constructing a new IP header that contains the mobile node’s care-of address as the destination IP address.

This new header then encapsulates the original IP datagram, causing the mobile node’s home address to have no effect on the encapsulated datagram’s routing until it arrives at the care-of address. This type of encapsulation is also called tunneling. After arriving at the care-of address, each datagram is de-encapsulated and then delivered to the mobile node.

The care-of address might belong to a foreign agent, or might be acquired by the mobile node through Dynamic Host Configuration Protocol (DHCP) or Point-to-Point Protocol (PPP). In the latter case, a mobile node is said to have a co-located care-of address.

The mobile node uses a special registration process to keep its home agent informed about its current location. Whenever a mobile node moves from its home network to a foreign network, or from one foreign network to another, it chooses a foreign agent on the new network and uses it to forward a registration message to its home agent.

Mobility agents (home agents and foreign agents) advertise their presence using agent advertisement messages. A mobile node can optionally solicit an agent advertisement message from any locally attached mobility agents through an agent solicitation message. A mobile node receives these agent advertisements and determines whether they are on its home network or a foreign network.

Want to learn more? Tonex offers Mobile IP Training, a 2-day course that introduces participants to the technical fundamentals of Mobile IP (MIP), a standard developed by IETF for the purpose of providing macro mobility across a set of different radio access technologies.

The course starts with an overview of mobility and wireless technology, including implementation issues. Mobile IP is also addressed, including operations, components and protocol. The course also includes sections with a summary of best practices to consider in Mobile IP operations and management.

For more information, questions, comments, contact us.

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