Cisco Systems 78-11741-02 manual How Mobile IP Works, Agent Discovery, IPC-161

Configuring Mobile IP

How Mobile IP Works

Figure 27 Mobile IP Components and Relationships
Mobile node	Mobile node
visiting foreign
network	at home

Foreign		Internet	Home
network	Foreign	Home	network
	agent	agent
Foreign
network	Foreign		53030
	agent

An MN is a node, for example, a PDA, a laptop computer, or a data-ready cellular phone, that can change its point of attachment from one network or subnet to another. This node can maintain ongoing communications while using only its home IP address.

An HA is a router on the home network of the MN that maintains an association between the home IP address of the MN and its care-of address, which is the current location of the MN on a foreign or visited network. The HA redirects packets by tunneling them to the MN while it is away from home.

An FA is a router on a foreign network that assists the MN in informing its HA of its current care-of address. The FA detunnels and delivers packets to the MN that were tunneled by the HA. The FA also acts as the default router for packets generated by the MN while it is connected to the foreign network.

It is recommended that HA and FA functionality be designed with interfaces with line protocol states that are normally up.

How Mobile IP Works

This section explains how Mobile IP works. The Mobile IP process includes three main phases, which are discussed in the following sections:

•Agent Discovery

•Registration

•Routing

Agent Discovery

During the agent discovery phase, HAs and FAs advertise their presence on their attached links by periodically multicasting or broadcasting messages called agent advertisements. MNs listen to these advertisements and determine if they are connected to their home link or a foreign link. Rather than waiting for agent advertisements, an MN can also send an agent solicitation. This solicitation forces any agents on the link to immediately send an agent advertisement.

Cisco IOS IP Configuration Guide

IPC-161