Mobile IP allows portable devices called Mobile Hosts (MHs) to roam from one area to another while maintaining the communication sessions. One requirement in mobile IP is that a legacy host communicating with a MH and the intermediate routers should not be modified. This requirement implies that a MH must continuously use its permanent IP address even as it roams to another area. Otherwise, existing sessions will stop working and new sessions should be restarted when a MH moves to another area.
Goals of Mobile IP
When people began demanding the ability to have mobile hosts, the IETF set up a Working Group to find a solution. The group quickly formulated a number of goals considered desirable in any solution. The major ones were the following.
- Every mobile host should be able to utilize its domicile IP address everywhere
- Any changes to the software were not permitted to the fixed hosts.
- No changes were permitted to the software of the router and its tables.
- Nearly all packets for mobile hosts are should not form any indirect route on their way.
- Overhead should not be acquired when a mobile host is at its domicile.
Working of Mobile IP
The mobile IP routing operates as follows:
When a Correspondent Host (CH) wants to send a packet to an MH, the CH transmits the standard IP packet with its address as the source IP address and the MH’s address as the destination IP address. This packet will be intercepted by the mobile host’s router called the Home Agent (HA), which keeps track of the current location of the MH. The HA manages all MHs in its home network that use the same address prefix. If the MH is located in the home network, then HA simply forwards the packet to its home network.
When a MH moves to a foreign network, it obtains a care-of-address from the Foreign Agent (FA) and registers the new address with it’s HA. The care of address reflects the MH’s current location and is typically the address of the FA. Once the HA knows the care-of-address of the MH, the HA can forward the registration packet to the MH via the FA. To Know more about mobile ip routing deeply visit the above given link.