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Mobile IP

Mobile IP. Lecture 5. Puzzle. K TIMES. WHY?. Muddy children problem N kids playing in the mud Only the foreheads of K kids get dirty A kid does not know if his/her forehead is dirty

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Mobile IP

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  1. Mobile IP Lecture 5

  2. Puzzle K TIMES. WHY? • Muddy children problem • N kids playing in the mud • Only the foreheads of K kids get dirty • A kid does not know if his/her forehead is dirty • One of the parents comes and asks all “dirty” kids to step forward. He keeps asking till all the dirty kids step forward. • How many times does the parent need to ask before kids step forward (all kids are honest, smart, and obedient)

  3. Outline • What is the problem at the routing layer when Internet hosts move?! • Can the problem be solved? • What is the standard solution? – mobile IP • What are the problems with the solution? • Other approaches?

  4. Internet hosts & Mobility • Wireless networking – allows Internet users to become mobile • As users move, they have to be handed over from one coverage area to another (since the coverage areas of access points are finite) … • Ongoing connections need to be maintained as the user moves …

  5. Problems? • What are the problems? • The IP address associated with a mobile host is network dependent! • When user connects to another network, IP address needs to change • Packets belonging to ongoing connections somehow need to be delivered to the mobile host

  6. Problems (Contd.)? • What are the options? • Make IP address host specific instead of network specific – obvious pitfalls? • Change IP address of host and start using the new IP address in the subsequent packets belonging to the connections

  7. Intuitive Solution • Take up the analogy of you moving from one apartment to another • What do you do? • Leave a forwarding address with your old post-office! • The old post-office forwards mails to your new post-office, which then forwards them to you

  8. Mobile IP Basics • Same as the post-office analogy • Two other entities – home agent (old post-office), foreign agent (new post-office) • Mobile host registers with home agent the new location • Home agent captures packets meant for mobile host, and forwards it to the foreign agent, which then delivers it to the mobile host

  9. HA MH MH SH FA Reverse path? • Same as in the post-office analogy • Packets originating from the mobile host go directly to the static corresponding host … • Hence the name • triangular routing

  10. Mobile IP Entities • Mobile host • Corresponding host • Home address • Care-of address • Home agent • Foreign agent

  11. Mobile IP in detail … • Combination of 3 separable mechanisms: • Discovering the care-of address • Registering the care-of address • Tunneling to the care-of address

  12. Discovering the care-of address • Discovery process built on top of an existing standard protocol: router advertisement (RFC 1256) • Router advertisements extended to carry available care-of addresses called: agent advertisements • Foreign agents (and home agents) send agent advertisements periodically • A mobile host can choose not to wait for an advertisement, and issue a solicitation message

  13. Agent advertisements • Foreign agents send advertisements to advertise available care-of addresses • Home agents send advertisements to make themselves known • Mobile hosts can issue agent solicitations to actively seek information • If mobile host has not heard from a foreign agent its current care-of address belongs to, it seeks for another care-of address

  14. Registering the Care-of Address • Once mobile host receives care-of address, it registers it with the home agent • A registration request is first sent to the home agent (through the foreign agent) • Home agent then approves the request and sends a registration reply back to the mobile host • Security?

  15. Registration Authentication • Mobile IP requires the home agent and mobile host to share a security association • MD5 with 128-bit keys to create digital signatures for registration requests to be used (registration message & header used for creating signature) • Any problems? – replay attacks • Solved by using an unique message identifier (timestamp or pseudorandom number)

  16. Illustration

  17. Foreign Agent Security? • No foreign agent authentication required • Foreign agent can potentially discard data once registration happens • However, the problem is same as in unauthenticated route advertisements (RFC 1256) in the wireline context

  18. Home agent discovery • If the mobile host is unable to communicate with the home agent, a home agent discovery message is used • The message is sent as a broadcast to the home agents in the home network

  19. Tunneling to the Care-of address • When home agent receives packets addressed to mobile host, it forwards packets to the care-of address • How does it forward it? - encapsulation • The default encapsulation mechanism that must be supported by all mobility agents using mobile IP is IP-within-IP (RFC 2003) • Using IP-within-IP, home agent inserts a new IP header in front of the IP header of any datagram

  20. Tunneling (contd.) • Destination address set to the care-of address • Source address set to the home agent’s address • Tunnel header uses 4 for higher protocol id – this ensures that IP after stripping out the first header, processes the packet again • Tunnel header of 55 used if IP minimal encapsulation used (RFC 2004)

  21. Illustration

  22. Recap • Host mobility and Internet addresses • Post-office analogy • Home agent, foreign agent, care-of address, home address • Registration and Tunneling • IPv6 and Mobility support …

  23. Puzzle • You have an unfair coin (prob(H) = p != ½) • How will you generate a fair toss?

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