- Forward


Mobile IP
An Introduction


Prof. David Bernstein
James Madison University

Computer Science Department
bernstdh@jmu.edu

Print

Motivation
Back Forward
  • 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
Back Forward
  • The Situation:
    • A device roams from network A to network B
  • Ideally:
    • The device keeps its IP address
Routing to Mobile Hosts
Back Forward
  • 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
Back Forward
  • 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
Back Forward
  • 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
There's Always More to Learn
Back -