MOBILE NETWORK LAYER

1. 1 MOBILE NETWORK LAYER Mobile IP

2. 2 Mobile IP (I) Mobile IP adds mobility support to the Internet network layer protocol IP. The Internet started at a time when no-one had a concept of mobile computers. The Internet of today lacks mechanisms for the support of users traveling through the world. IP is the common base for thousands of applications and runs over dozens of different networks; this is the reason for supporting mobility at the IP layer. Motivation for Mobile IP: Routing based on IP destination address, network prefix determines physical subnet Change of physical subnet implies change of IP address to have a topological correct address (standard IP) or needs special entries in the routing tables

3. 3 Mobile IP (II) Create specific routes to end-systems � mobile nodes? change of all routing table entries to forward packets to the right destination does not scale with the number of mobile hosts and frequent changes in the location Changing the IP address? adjust the host IP address depending on the current location almost impossible to find a mobile host, DNS has not been built for frequent updates TCP connection break

4. 4 Mobile IP (III) Requirements to Mobile IP: Transparency mobile end-systems keep their IP address continuation of communication after interruption of link possible point of connection to the fixed network can be changed Compatibility support of the same layer 2 protocols as IP does no changes to current end-systems and routers required Mobile end-systems can communicate with fixed systems

5. 5 Mobile IP (IV) Security authentication of all registration messages Efficiency and scalability only little additional messages to the mobile system required (connection typically via a low bandwidth radio link) world-wide support of a large number of mobile systems in the whole Internet

6. 6 Real-life 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 mail to your new post-office, which then delivers it to you Same Principle as call forwarding! Same Principle as call forwarding!

7. 7 Mobile IP - Definition �Mobile IP (MIP) is a modification to IP that allows nodes to continue to receive datagrams no matter where they happen to be attached to the Internet� Same Principle as call forwarding! Same Principle as call forwarding!

8. 8 Mobile IP (V) Terminology: Mobile Node (MN) system (node) that can change the point of connection to the network without changing its IP address Home Agent (HA) system in the home network of the MN, typically a router registers the location of the MN, tunnels IP datagrams to the COA Foreign Agent (FA) system in the current foreign network of the MN, typically a router forwards the tunneled datagrams to the MN, typically also the default router of the MN

9. 9 Mobile IP (VI) Care-of Address (COA) address of the current tunnel end-point for the MN (at FA or MN) actual location of the MN from an IP point of view can be chosen, e.g., via DHCP Correspondent Node (CN) communication partner

10. 10 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 Going back to the basic process we can have all the functions acting independently.Going back to the basic process we can have all the functions acting independently.

11. 11 Mobile IP in detail These diagrams show the different signaling messages needed to establish a mobile IP connection and communication. The diagram on the left is for MIPv4 and the one on the right is for MIPv6 In MIPv4 we see that the HA is the one taking care of the triangular routing, whereas is MIPv6 this responsibility is delegated to the mobile node. IPv6 and MIPv6 were designed from the beginning with mobility in mind and support these functions in a more simple way These diagrams show the different signaling messages needed to establish a mobile IP connection and communication. The diagram on the left is for MIPv4 and the one on the right is for MIPv6 In MIPv4 we see that the HA is the one taking care of the triangular routing, whereas is MIPv6 this responsibility is delegated to the mobile node. IPv6 and MIPv6 were designed from the beginning with mobility in mind and support these functions in a more simple way

12. 12 Discovering the care-of address Discovery process built on top of an existing standard protocol: router advertisements 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. 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. 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. 15 Registration Illustration

16. 16 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

17. 17 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 Using IP-within-IP, home agent inserts a new IP header in front of the IP header of any datagram

18. 18 Tunneling (contd.) Destination address set to the care-of address Source address set to the home agent�s address After stripping out the first header, IP processes the packet again

19. 19 Tunneling Illustration

20. 20 Mobile IP (VII) Example network

21. 21 Mobile IP (VIII) Data transfer to the mobile system

22. 22 Mobile IP (IX) Data transfer from the mobile system

23. 23 Mobile IP (XIII) Optimization of packet forwarding: Triangular routing sender sends all packets via HA to MN higher latency and network load Solutions � optimization HA informs a sender about the location of MN sender learns the current location of MN direct tunneling to this location big security problems!

24. 24 Mobile IP (XIV) Change of FA Packets on-the-fly during the change can be lost new FA informs old FA to avoid packet loss, old FA forwards remaining packets to new FA this information also enables the old FA to release resources for the MN

25. 25 Mobile IP (XV) Change of the foreign agent with the optimized mobile IP

26. 26 Mobile IP (XVI)

27. 27 Mobile IP (XVII) Mobile IP with reverse tunneling Router accept often only �topological correct� addresses (firewall!) a packet from the MN encapsulated by the FA is now topological correct furthermore multicast and TTL problems solved (TTL in the home network correct, but MN is to far away from the receiver) Reverse tunneling does not solve problems with firewalls, the reverse tunnel can be abused to circumvent security mechanisms (tunnel hijacking) optimization of data paths, i.e. packets will be forwarded through the tunnel via the HA to a sender (double triangular routing) The standard is backwards compatible the extensions can be implemented easily and cooperate with current implementations without these extensions Agent Advertisements can carry requests for reverse tunneling

28. 28 Mobile IP in detail USE POINTER Mobile IP (MIP) allows IP nodes to maintain connectivity while moving A Mobile Node (MN) is assigned a Care-of Address (CoA) when it moves to a foreign sub-network The COA can be an address obtained by the FA OR AN ADDRESS OBTAINED DYNAMICALLY The Home Agent will intercept and tunnel all packets to the MNs CoA A Foreign Agent (FA) or the MN will de-tunnel the packets and eventually set up a direct connection with the CH via an Optimal Route USE POINTER Mobile IP (MIP) allows IP nodes to maintain connectivity while moving A Mobile Node (MN) is assigned a Care-of Address (CoA) when it moves to a foreign sub-network The COA can be an address obtained by the FA OR AN ADDRESS OBTAINED DYNAMICALLY The Home Agent will intercept and tunnel all packets to the MNs CoA A Foreign Agent (FA) or the MN will de-tunnel the packets and eventually set up a direct connection with the CH via an Optimal Route

29. 29 Route Optimizations Enable direct notification of the corresponding host Direct tunneling from the corresponding host to the mobile host Binding cache maintained at corresponding host

30. 30 Route optimizations (contd.) 4 types of messages Binding update Binding request Binding warning Binding acknowledge

31. 31 Binding Update When a home agent receives a packet to be tunneled to a mobile host, it sends a binding update message to the corresponding host When a home agent receives a binding request message, it replies with a binding update message Also used in the the smooth-handoffs optimization

32. 32 Binding Update (Contd.) Corresponding host caches binding and uses it for tunneling subsequent packets Lifetime of binding? Corresponding host that perceives a near-expiry can choose to ask for a binding confirmation using the binding request message Home agent can choose to ask for an acknowledgement to which a corresponding host has to reply with a binding ack message

33. 33 Binding warning When a foreign agent receives a tunneled message, but sees no visitor entry for the mobile host, it generates a binding warning message to the appropriate home agent When a home agent receives a warning, it issues an update message to the corresponding host What if the foreign agent does not have the home agent address (why?) ?

34. 34 Binding Update and Warning

35. 35 Mobile IP and IPv6 Mobile IP was developed for IPv4, but IPv6 simplifies the protocols security is integrated and not an add-on, authentication of registration is included COA can be assigned via auto-configuration (DHCPv6 is one candidate), every node has address autoconfiguration no need for a separate FA, all routers perform router advertisement which can be used instead of the special agent advertisement; addresses are always co-located MN can signal a sender directly the COA, sending via HA not needed in this case (automatic path optimization) �soft� hand-over, i.e. without packet loss, between two subnets is supported MN sends the new COA to its old router the old router encapsulates all incoming packets for the MN and forwards them to the new COA authentication is always granted

36. 36 Problems with mobile IP Security authentication with FA problematic, for the FA typically belongs to another organization no protocol for key management and key distribution has been standardized in the Internet patent and export restrictions Firewalls typically mobile IP cannot be used together with firewalls, special set-ups are needed (such as reverse tunneling) QoS many new reservations in case of RSVP tunneling makes it hard to give a flow of packets a special treatment needed for the QoS Security, firewalls, QoS etc. are topics of current research and discussions!

37. 37 Security in Mobile IP Security requirements (Security Architecture for the Internet Protocol, RFC 1825) Integrityany changes to data between sender and receiver can be detected by the receiver Authenticationsender address is really the address of the sender and all data received is really data sent by this sender Confidentialityonly sender and receiver can read the data Non-Repudiationsender cannot deny sending of data Traffic Analysiscreation of traffic and user profiles should not be possible Replay Protectionreceivers can detect replay of messages

38. 38 IP Micro-mobility support Micro-mobility support: Efficient local handover inside a foreign domainwithout involving a home agent Reduces control traffic on backbone Especially needed in case of route optimization Example approaches: Cellular IP HAWAII Hierarchical Mobile IP (HMIP) Important criteria: Security Efficiency, Scalability, Transparency, Manageability

39. 39 Cellular IP Operation: �CIP Nodes� maintain routing entries (soft state) for MNs Multiple entries possible Routing entries updated based on packets sent by MN CIP Gateway: Mobile IP tunnel endpoint Initial registration processing Security provisions: all CIP Nodes share�network key� MN key: MD5(net key, IP addr) MN gets key upon registration

40. 40 Cellular IP: Security Advantages: Initial registration involves authentication of MNsand is processed centrally by CIP Gateway All control messages by MNs are authenticated Replay-protection (using timestamps) Potential problems: MNs can directly influence routing entries Network key known to many entities(increases risk of compromise) No re-keying mechanisms for network key No choice of algorithm (always MD5, prefix+suffix mode) Proprietary mechanisms (not, e.g., IPSec AH)

41. 41 Cellular IP: Other issues Advantages: Simple and elegant architecture Mostly self-configuring (little management needed) Integration with firewalls / private address support possible Potential problems: Not transparent to MNs (additional control messages) Public-key encryption of MN keys may be a problemfor resource-constrained MNs Multiple-path forwarding may cause inefficient use of available bandwidth

42. 42 HAWAII Operation: MN obtains co-located COAand registers with HA Handover: MN keeps COA,new BS answers Reg. Requestand updates routers MN views BS as foreign agent Security provisions: MN-FA authentication mandatory Challenge/Response Extensions mandatory

43. 43 HAWAII: Security Advantages: Mutual authentication and C/R extensions mandatory Only infrastructure components can influence routing entries Potential problems: Co-located COA raises DHCP security issues(DHCP has no strong authentication) Decentralized security-critical functionality(Mobile IP registration processing during handover)in base stations Authentication of HAWAII protocol messages unspecified(potential attackers: stationary nodes in foreign network) MN authentication requires PKI or AAA infrastructure

44. 44 HAWAII: Other issues Advantages: Mostly transparent to MNs(MN sends/receives standard Mobile IP messages) Explicit support for dynamically assigned home addresses Potential problems: Mixture of co-located COA and FA concepts may not besupported by some MN implementations No private address support possiblebecause of co-located COA

45. 45 Hierarchical Mobile IPv6 (HMIPv6) Operation: Network contains mobility anchor point (MAP) mapping of regional COA (RCOA) to link COA (LCOA) Upon handover, MN informsMAP only gets new LCOA, keeps RCOA HA is only contacted if MAPchanges Security provisions: no HMIP-specificsecurity provisions binding updates should be authenticated

46. 46 Hierarchical MIP

47. 47 Hierarchical Mobile IP: Security Advantages: Local COAs can be hidden,which provides some location privacy Direct routing between CNs sharing the same link is possible (but might be dangerous) Potential problems: Decentralized security-critical functionality(handover processing) in mobility anchor points MNs can (must!) directly influence routing entries via binding updates (authentication necessary)

48. 48 Hierarchical Mobile IP: Other issues Advantages: Handover requires minimum numberof overall changes to routing tables Integration with firewalls / private address support possible Potential problems: Not transparent to MNs Handover efficiency in wireless mobile scenarios: Complex MN operations All routing reconfiguration messages sent over wireless link

49. 49 Smooth Hand-offs When a mobile host moves from one foreign agent to another � Packets in flight to the old FA are lost and are expected to be recovered through higher layer protocols (e.g. TCP) How can these packets be saved?

50. 50 Smooth Hand-offs Make previous FA forward packets to the new FA Send binding updates to the old FA through the new FA Such forwarding will be done for a pre-specified amount of time (registration lifetime) Update can also help old FA free any reserved resources immediately Why better?

51. 51 Recap Host mobility and Internet addresses Post-office analogy Home agent, foreign agent, care-of address, home address Registration and Tunneling Mobile IP problems Mobile IP Optimizations Other options