Mobile IP

JMU

Mobile IP
An Introduction

Prof. David Bernstein
James Madison University

Computer Science Department

bernstdh@jmu.edu

Motivation

The Problem with Mobile Devices:
- IP addresses indicate a network location
- So, a change of location requires a change in IP address
Using DHCP to Provide Mobility:
- Assign a new IP address when you move
- But this causes problems for hosts/applications that think they know your IP

Objective of Mobile IP

The Situation:
- A device roams from network A to network B
Ideally:
- The device keeps its IP address

Routing to Mobile Hosts

Participants:
- Home agent
- Foreign agent
- Mobile host
A Useful Tool:
- IP tunneling
- Home agent wraps packet in IP packet with address of the foreign host
- Foreign agent receives packet and strips it
Roles:
- Home agent impersonates the mobile host
- Home agent wraps packet in IP packet with address of the foreign host
- Foreign agent receives packet and strips it

Routing Details

The source wants to send to a mobile device
An ARP request is issued for that device
The home agent replies with its MAC address
The source sends the packet to the home agent
The home agent wraps the packet in an IP packet destined for the foreign agent
The home agent transmits the wrapped packet to the foreign agent
The foreign agent receives the wrapped packet
The foreign agent strips the wrapped packet
The foreign agent delives the original packet to the mobile device

Setup

Discovery:
- The home agent maintains information about the mobile host
- Networks send advertisement messages that mobile hosts use to identify them
Registration:
- When a mobile host joins a foreign network its home and foreign agents update registration information