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Mobile IP Agent Discovery, and Agent Advertisement and Solicitation Messages
(Page 1 of 5)
When a mobile node is first turned
on, it cannot assume that it is still at home the way normal
IP devices do. It must first determine where it is, and if it is not
at home, begin the process of setting up datagram forwarding from its
home network. This process is accomplished by communicating with a local
router serving as an agent, through the process called agent discovery.
Agent Discovery Process
Agent discovery encompasses the first
three steps in the simplified five-step Mobile IP operational summary
I gave in the
topic on general operation. The main goals
of agent discovery include the following:
- Agent/Node Communication: Agent discovery
is the method by which a mobile node first establishes contact with
an agent on the local network to which it is attached. Messages are
sent from the agent to the node containing important information about
the agent; a message can also be sent from the node to the agent asking
for this information to be sent.
- Orientation: The node uses the agent discovery
process to determine where it is. Specifically, it learns whether it
is on its home network or a foreign network by identifying the agent
that sends it messages.
- Care-Of Address Assignment: The agent
discovery process is the method used to tell a mobile node the care-of
address it should use, when foreign agent
care-of addressing is used.
Mobile IP agents are routers that
have been given additional programming to make them Mobile IP
aware. The communication between a mobile node and the agent on
its local network is basically the same as the normal communication
required between a device on an IP network and its local router, except
more information needs to be sent when the router is an agent.
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The TCP/IP Guide (http://www.TCPIPGuide.com)
Version 3.0 - Version Date: September 20, 2005
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