What is mobile ip and how does it work

The Mobile Internet Protocol, or better known as Mobile IP, is a protocol that adds to the already existing Internet Protocol by making the movement of a node transparent to applications on its original network.

One knows that a host address is made up of a network number and a host part. This network number tells the user what network the host is attached to. Original Internet Protocol algorithms tell certain routers how to get packets to their correct networks. Now with the regular Internet Protocol if the host disconnected itself from its original network and joined another network, the host would never receive any packets because the host has the same IP address from its old network that would not be recognized by the network in which it joined. In essence the host would seem to be missing because its IP address does not match its new network number and therefor would never recieve any packets.

Because this problem exists, Mobile IP was created so that mobile nodes could freely move from network to network without the fear of losing data or interrupting current computer applications and settings.

The next logical step after figuring out what Mobile IP is is to discover exactly how it works. Mobile IP is unique because it allows the mobile node to use two IP addresses. One of those addresses is the mobile nodes “home address”. The “home address” is an IP address that makes it seem like the mobile node will always be able to receive data on its “home network”. A “home agent”, which is a network node, has the function of acquiring all data that is being sent to the mobile node and then arranging for it to be sent to the mobile nodes current location. When a mobile node is not on its home network, it is said to be on a “foreign network”. This “foreign network” uses another IP address for the “foreign agent”, a network node that the mobile node is attached to, which is known as the “care-of address”. This IP address changes depending on the nodes point of attachment. The mobile node then registers with the “foreign agent” and gives it the address of its home agent. This allows the home network to know exactly where the mobile node is located and therefore will be able to know where to send packets or data. In essence whenever the mobile node moves, it registers another “care-of address” with the mobile nodes “home agent”. This is a simplified overview of how Mobile IP functions.

How Is the Care-of Address Discovered?

In order to discover the Care-of Address , Mobile IP has built on top of the already existing protocol called Router Advertisement. Router advertisements contain information about the default routers and no other information. Mobile IP extended this protocol by adding the Care-of Address to the existing routing advertisement. This new form of the routing edvertisement is called the Agent Advertisement. To summarize without going into added detail, the agent advertisement performs the following functions:

1)allows for detection of mobility agents

2) lists all care-of addresses needed, be it one or more

3) informs the mobile node of special features provided by foreign agents

4) lets mobile nodes determine the network number and the status of their link to the internet

5) lets the mobile node know what kind of agent it is attached to, the home agent, foreign agent or maybe even both of them. This in essence tell the mobile node if it is on its home network or not.

How is the Care-of Address Registered?

In order to make use of this care-of address, the home agent must know about it before it can begin packet forwarding. The mobile nodes registers this care-of address by following four steps:

1) sending a registration request that contains the care-of address information to its home agent

2) having the home agent add the necessary information to its routing table once it recieves the request

3) approving the request and lastly

4) having the home agent send a registration reply back to the mobile node.