Mobile IP : Mobile IP Radadiya Bankim
Computer Science Department,
Saurashtra University, Rajkot
firstname.lastname@example.org Table of Contents : Introduction
Components of Mobile IP
Discovering the care-of address
Registering the care-of address
Route Optimization Table of Contents Slide 3: Connections endpoints identified by the source and destination address and ports.
Source address 220.127.116.11, source port 9878, destination address 18.104.22.168, destination port 21
Changing of the address of either side breaks the connection Introduction TCP/IP Connections Slide 4: IP addresses are used for two purposes:
Delivering packets to interfaces (routing)
Identifying end points of connections (hosts)
Address depends on the network topology
Connections are bound to the address
The dual nature of IP addresses is problematic for mobile nodes: Address of the node should always be topologically correct, but this would break the connections bound to previous addresses Introduction IP addresses as identifiers Slide 5: Two problems:
Hide mobility from applications
Deliver packets to Mobile Nodes
Hiding the mobility from applications preserves the connections despite changes in the address of Mobile Node
If Mobile Node needs to be reachable, it needs a mobility agent service to keep track of its current address Introduction Managing Node Mobility Slide 6: Proposed as a standard protocol that builds on the Internet Protocol by making mobility transparent to applications and higher level protocols like TCP in November 1996 by IETF(Internet Engineering Task Force).
Was designed to solve these two problems by allowing the mobile node to use two IP addresses:
a fixed home address, to identify i.e. TCP connections.
a care-of address that changes at each new point of attachment.
Allows IP packets to be routed to a mobile node regardless of its current point-of-attachment. Overview Definition of Mobile IP Overview : Overview The binding of home-address and care-of-address is maintained by a specialized routers, known as mobility agents.
Two types of mobility agents:
Foreign agents Mobility Agents Overview : Overview Home agents maintain mobility binding in their mobility binding table. Home Agents Overview : Overview Foreign Agents Foreign agents maintain visitor tables which contain all mobile nodes currently visiting them. Overview : Overview Mobility Agents Components of Mobile IP : Components of Mobile IP Three main components of Mobile IP:
Discovering the care-of address – mobile node uses discovery procedure to identify prospective home and foreign agents
Registering the care-of address – mobile node uses an authenticated registration procedure to inform home agent of its care-of address
Tunneling the care-of address – used to forward IP datagrams from a home address to a care-of address Discovering the care-of address : Discovering the care-of address The Mobile IP discovery process has been built on top of an existing standard protocol, Router Advertisement
Mobile IP discovery does not modify the original fields of existing router advertisements but simply extends them to carry information about one or more care-of adresses.
Known as Agent Advertisements
Mobile node is responsible for ongoing discovery process
Must determine if it is attached to its home network or a foreign network
Transition from home network to foreign network can occur at any time without notification to the network layer Discovering the care-of address : Home agents and foreign agents typically broadcast agent advertisements at regular intervals
Mobile node listens for agent advertisement messages
If a mobile node needs to get a care-of address and does not wish to wait for the periodic advertisement, the mobile node can broadcast or multicast a solicitation that will be answered by any foreign agent or home agent that receives it. Discovering the care-of address Registering the care-of address : Registering the care-of address MN=Mobile node FA= Foreign agent HA = Home agent
Sends Request ®
Relays Request ®
Grant or Deny
¬ Sends Reply
¬ Relays Reply Used to notify home agent about new or renew association with care-of address and home agent uses information to create tunnel to mobile node. Registering the care-of address : Foreign agent is passive in registration (not allowed to originate any request or reply e.g. when lifetime exceeds).
Relays registrations messages
When provides care-of address it decapsulates datagrams for mobile node
Keeps visitor list Foreign Agent Role Registering the care-of address Registering the care-of address : Home agent is reactive in registration (replays to requests). After receiving valid request it updates mobility bindings for this mobile node and issues suitable replay
Allowed only to reply valid requests Home Agent Role Registering the care-of address IP Tunneling : IP Tunneling Tunneling the care-of address – IP Tunneling IP tunneling, known as IP-within-IP encapsulation, is used to deliver IP packets to a mobile node when it is not in its home network.
Home agent tunnels IP packets to the care-of-address. IP Tunneling : IP Tunneling IP Tunneling : IP Tunneling Minimal Encapsulation Too much overhead in IP tunneling because some fields of the inner IP header are duplicated.
Minimal Encapsulation prevents the overhead by modifying the original IP header. IP Tunneling : IP Tunneling Route Optimization : Route Optimization drawbacks:
waste of network resources
Home Agent is a bottleneck Triangle routing Route Optimization : Route Optimization Binding updates : Correspondent host receives (from home agent) a binding update informing mobile host’s current care-of-address, when the home agent receives a packet from the correspondent host + the packet is forwarded
Correspondent host can cache the binding, and future packets can be tunneled directly to the care-of-address (without going via home agent)
Cache consistency: A cached binding becomes stale when the mobile host moves Route Optimization : Route Optimization Route Optimization : Route Optimization Binding warning: Used by old foreign agent, to request the home agent to send current binding to a correspondent host.
When a host moves:
Old foreign agent may cache a forwarding pointer to the new foreign agent: packets re-tunneled along the forwarding pointer + binding warning sent to home agent to update the correspondent with the new binding
Old foreign agent may not cache (or purge) the forwarding pointer: packets forwarded to home agent. Home agent tunnels it to current care-of-address + sends binding update to correspondent