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The
Mobile IP protocol allows location-independent routing of IP datagrams on the Internet.
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Each
mobile node is identified by its home address disregarding its current location
in the Internet. While away from its home network, a mobile node is associated
with a care-of address which identifies its current location and its
home address is associated with the local endpoint of a tunnel to its home
agent.
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Mobile
IP specifies how a mobile node registers with its home agent and how the home agent
routes datagrams to the mobile node through the tunnel.
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Mobile
IP provides an efficient, scalable mechanism for roaming within the Internet. Using
Mobile IP, nodes may change their point-of-attachment to the Internet without changing
their home IP address.
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Mobile
IP allows portable devices called mobile hosts (MHs) to roam from one area to another.
A common analogy to understand Mobile IP is that when someone moves his
residence from one location to another. Person moves from Boston to New York.
Person drops off new mailing address to New York post office. New York post
office notifies Boston post office of new mailing address. When Boston post
office receives mail for person it knows to forward mail to person's New York
address. The below figure describes the mobile hosts routing
Figure: Routing
for mobile hosts
Mobile IP operates as
follows:-
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When
a correspondent host (CH) wants to send a packet to MH, the CH transmits the standard
IP packet with its address as the source IP address and MH’s address as destination
IP address.
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This
packet will be intercepted by the mobile host’s router called 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
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If
the MH is located in the home network, the HA simply forwards the packet to its
home network.
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When
an MH moves to a foreign network, the MH obtains a care of address from the foreign
agent (FA) and registers the new address with its HA. The care-of-address reflects
the MH’s current location and is typically the address of FA.
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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 transmit a
packet by HA to MH directly when MH is in foreign network, instead of using FA,
tunneling mechanisms is used. It has two addresses,
· Destination
address of the other end of the tunnel (FA) and Final destination MH.
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