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Mobile Internet Protocol (or Mobile IP)

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Mobile IP is a communication protocol (created by extending Internet Protocol, IP) that allows the users to move from one network to another with the same IP address. It ensures that the communication will continue without the user’s sessions or connections being dropped. 


  1. Mobile Node (MN) is the hand-held communication device that the user carries e.g. Cell phone.
  2. Home Network is a network to which the mobile node originally belongs as per its assigned IP address (home address).
  3. Home Agent (HA) is a router in-home network to which the mobile node was originally connected
  4. Home Address is the permanent IP address assigned to the mobile node (within its home network).
  5. Foreign Network is the current network to which the mobile node is visiting (away from its home network).
  6. Foreign Agent (FA) is a router in a foreign network to which the mobile node is currently connected. The packets from the home agent are sent to the foreign agent which delivers them to the mobile node.
  7. Correspondent Node (CN) is a device on the internet communicating to the mobile node.
  8. Care-of Address (COA) is the temporary address used by a mobile node while it is moving away from its home network.
  9. Foreign agent COA, the COA could be located at the FA, i.e., the COA is an IP address of the FA. The FA is the tunnel end-point and forwards packets to the MN. Many MN using the FA can share this COA as a common COA.
  10.  Co-located COA, the COA is co-located if the MN temporarily acquired an additional IP address which acts as COA. This address is now topologically correct, and the tunnel endpoint is at the MN. Co-located addresses can be acquired using services such as DHCP.
Mobile IP

Mobile IP


The correspondent node sends the data to the mobile node. Data packets contain the correspondent node’s address (Source) and home address (Destination). Packets reach the home agent. But now mobile node is not in the home network, it has moved into the foreign network. The foreign agent sends the care-of-address to the home agent to which all the packets should be sent. Now, a tunnel will be established between the home agent and the foreign agent by the process of tunneling. 

Tunneling establishes a virtual pipe for the packets available between a tunnel entry and an endpoint. It is the process of sending a packet via a tunnel and it is achieved by a mechanism called encapsulation. 

Now, the home agent encapsulates the data packets into new packets in which the source address is the home address and destination is the care-of-address and sends it through the tunnel to the foreign agent. Foreign agent, on another side of the tunnel, receives the data packets, decapsulates them, and sends them to the mobile node. The mobile node in response to the data packets received sends a reply in response to the foreign agent. The foreign agent directly sends the reply to the correspondent node. 

Key Mechanisms in Mobile IP: 

  1. Agent Discovery: Agents advertise their presence by periodically broadcasting their agent advertisement messages. The mobile node receiving the agent advertisement messages observes whether the message is from its own home agent and determines whether it is in the home network or foreign network.
  2. Agent Registration: Mobile node after discovering the foreign agent sends a registration request (RREQ) to the foreign agent. The foreign agent, in turn, sends the registration request to the home agent with the care-of-address. The home agent sends a registration reply (RREP) to the foreign agent. Then it forwards the registration reply to the mobile node and completes the process of registration.
  3. Tunneling: It establishes a virtual pipe for the packets available between a tunnel entry and an endpoint. It is the process of sending a packet via a tunnel and it is achieved by a mechanism called encapsulation. It takes place to forward an IP datagram from the home agent to the care-of-address. Whenever the home agent receives a packet from the correspondent node, it encapsulates the packet with source address as home address and destination as care-of-address.

Route Optimization in Mobile IP: 

The route optimization adds a conceptual data structure, the binding cache, to the correspondent node. The binding cache contains bindings for the mobile node’s home address and its current care-of-address. Every time the home agent receives an IP datagram that is destined to a mobile node currently away from the home network, it sends a binding update to the correspondent node to update the information in the correspondent node’s binding cache. After this, the correspondent node can directly tunnel packets to the mobile node. Mobile IP is provided by the network providers.

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Last Updated : 18 May, 2022
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