What is Mobile IP ?
Mobile IP is an open standard defined by IETF. It allows user to maintain same IP address and stay connected with ongoing applications while roaming between networks.
If a mobile computer, or mobile node, moves to a new network while keeping its IP address unchanged, its address does not reflect the new point of attachment.
Consequently, existing routing protocols cannot route datagrams to the mobile node correctly. In this situation, you must reconfigure the mobile node with a different IP address representative of its new location, which is a cumbersome process. Thus, under the current Internet Protocol, if the mobile node moves without changing its address, it loses routing; but if it does change its address, it loses connections.
Why Mobile IP ?
Mobile IP solves this problem by allowing the mobile node to use two IP addresses: a fixed Home address and a Care of address that changes at each new point of attachment. Mobile IP enables a computer to roam freely on the Internet or an organization’s network while still maintaining the same home address.
What is Care of Address?
The Care of address is an IP address of the foreign agent. A foreign agent provides a foreign agent Care of address through its agent advertisement messages. Many mobile nodes can share the same Care of address. This
sharing reduces demands on the IPv4 address space
Components of Mobile IP:
- Mobile Node (MN)–Host or router that changes its point of attachment from one network to another.
- Home Agent (HA)–Router on a mobile node’s home network that intercepts datagrams destined for the mobile node, and delivers them through the Care of address. The home agent also maintains current location information for the mobile node.
- Foreign Agent (FA)–Router on a mobile node’s visited network that provides routing services to the mobile node while the mobile node is registered.
How Mobile IP Works?
Here a mobile node (220.127.116.11/24) moves from network AP1 (Home network) to network AP2 ( Foreign Network) and maintaining same internet connection. A node is having two different address a home address and care of address.
The whole process is divided into three major steps:
- Agent Discovery
Step 1: 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.
Step 2 : 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.
Step 3 :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 is called tunneling.
Step 4: 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.
Step 5 : 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.
Step 6 : A mobile node receives these agent advertisements and determines whether they are on its home network or a foreign network. When the mobile node detects that it is located on its home network, it operates without mobility services. If returning to its home network from being registered elsewhere, the mobile node de-registers with its home agent.
What is Foreign Agent?
The foreign agent plays a mostly passive role in Mobile IP registration. A foreign agent adds all registered mobile nodes to its visitor table. It also sends periodic agent advertisement messages to advertise its presence.
What is Home Agent?
Home agents play an active role in the registration process. The home agent receives registration requests from the mobile node (perhaps relayed by a foreign agent), updates its record of the mobility bindings for this mobile node, and issues a suitable registration reply in response to each. The home agent also forwards packets to the mobile node when the mobile node is away from its home network.