1 CIS 6930: Mobile Computing Mobile IP Sumi Helal Credit: majority of slides borrowed from one of Dave Johnson’s talks, 3

2 References 4 2.1: C. Perkins and A. Myles, "Mobile IP," technical report : B. Lancki, A. Dixit, V. Gupta, "Mobile-IP: Supporting Transparent Host Migration on the Internet," Linux Journal, June : D. Johnson and D. Maltz. "Protocols for Adaptive Wireless and Mobile Networkig", IEEE Personal Communication, 3(1), February : C. Perkins and D. Johnson. "Mobility Support in IPv6," Proceedings of the Second Annual International Conference on Mobile Computing and Networking (MobiCom'96), November : M. Baker, X. Zhao, S. Cheshire, J. Stone, Stanford University, "Supporting Mobility in MosquitoNet", USENIX Winter 1996

3 Internet Protocol (IP) 4 Connectionless packet delivery 4 Unreliable delivery 4 IP host addresses consist of two parts –network id –host id 4 By design, host address is tied to its network

4 Internet Protocol (IP) 4 Intermediate routers need only look at the network id 4 destination network responsible to get packet to right host 4 When a host moves to a new network, its IP address would have to change - packets to old address lost

5 Mobile IP

6 IETF Mobile IP Protocol (refer paper by Johnson & Maltz) 4 IETF = Internet Engineering Task Force: Standards development body for the Internet 4 Mobile IP allows a host to have a unique (location-independent) IP address. 4 Each host has a home agent on its home network. –The home agent forward IP packets when mobile host away from home.

7 IETF Mobile IP Protocol (refer paper by Johnson & Maltz) 4 When away from home, mobile host has a care-of-address –care-of-address = address of foreign agent within the foreign subnet - the foreign agent delivers forwarded packets to mobile host –care-of-address may also be a temporary IP address on the foreign network

8 Basic Architecture

9 IETF Mobile IP 4 When moving, the host register with home agent - home agent always knows the host’s current care-of-address. 4 Correspondent host = Host that wants to send packets to the mobile host 4 Correspondent host sends packets to the host’s IP address, which are routed to the host’s home network.

10 IETF Mobile IP 4 Correspondent host need not know that the destination is mobile. 4 Home agent encapsulates and tunnels packets to the mobile host’s care-of- address.

11 Encapsulation and Tunneling 4 IP-in-IP encapsulation 4 Received IP packet is encapsulated in a new IP packet with a new header. In the new header: –Destination = care-of-address –Source = address of home agent –Protocol number = IP-in-IP

12 Encapsulation and Tunneling 4 Encapsulation protocol at foreign agent removes added header, and transmits the packet to the mobile host over the local network interface

13 IP-in-IP Encapsulation

14 Minimal Encapsulation 4 Reduces the additional bytes added to header when encapsulating: 8 or 12 bytes are added. –Original source address need not be included in the tunnel header, if the original source is also the tunneling node

15 Authentication 4 As host B can send “moving to new location” registration messages to host A’s home server, host B can pretend to be host A, and receive packets destined for host A. 4 To avoid this, all registration messages must be “authenticated”. 4 Protection against “replay” attacks must be provided.

16 Route Optimizations 4 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 4 Correspondent host can cache the binding, and future packets can be tunneled directly to the care-of-address (without going via home agent) 4 Cache consistency: A cached binding becomes stale when the mobile host moves

17 Route Optimization

18 Route Optimizations 4 Binding warning: Used by old foreign agent, to request the home agent to send current binding to a correspondent host. 4 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

19 Route Optimization 4 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

20 4 No foreign agent 4 Visiting mobile host is assigned a temporary IP address corresponding to the foreign subnet. 4 Packets are tunneled directly to the mobile host (without having to go through a foreign agent) MosquitoNet

21 MosquitoNet -- Advantages 4 Mobile hosts can visit networks that do not have home agents 4 Foreign agent is no more a single point of failure 4 Scalability: Foreign agent not needed on every network that a mobile may visit. Home agents only needed on networks with mobile clients 4 Simpler protocol: Only part of foreign agent functionality needed

22 MosquitoNet -- Disadvantages 4 Mobile host needs to acquire a temporary IP on foreign subnet 4 Security: If a temporary IP address is re-assigned to another mobile to soon, the new mobile may receive packets intended for the previous mobile. 4 Packet loss: Foreign agents can forward packets destined for a mobile host that has moved to another foreign subnet. Without foreign agents, the packets will simply be lost. 4 Mobile host is more complex, as it must incorporate some of the functionality of a foreign agent.

23 Other Protocols: CDPD 4 CDPD: Cellular Digital Packet Data 4 Similarity to Mobile IP: – triangular routing approach between mobile host and home and foreign agents 4 Differences: –User IP assigned by CDPD service provider –Uses prop. Tunneling not IP-in-IP –Not strictly above the data link layer

24 Other Protocols: GPRS 4 GPRS: General Packet Radio Data GSN: GPRS Support Node MSC: Mobile Switching Center BTS: Base Transciever Station BSC: Base Station Controller

25 Mobile IP vs. CDPD vs. GPRS 4 CDPD is slowing down (today Jan 1999) 4 Mobile IP is big in the US. IETF is behind it 4 US industry just started adapting Mobile IP (Sisco routers!). 4 Motorola’s iDEN network is Mobile IP based. 4 Microsoft’s position is not clear yet. Would they finally bundle it with Windows CE? 4 Europe: Initial copying of Mobile IP efforts. But now do have the advantages of wider interoperability (which is a UMTS requirement)