Mobility Management - Basics

Transcription

1 Mobility Management - Basics Summer Semester 2012 Integrated Communication Systems Group Ilmenau University of Technology

2 Content Motivation Problem and possible solutions IP-based mobility management Conclusions and future work References Advanced Networking, Master Program 2

3 Motivation Advanced Networking, Master Program 3

4 Motivation The Internet and mobile communication networks are experiencing an enormous growth Future networks will interconnect various heterogeneous networks by means of a common IP core, also referred to as All-IP Goals: always-on connectivity, higher bandwidth, reduced delay, lower cost, etc. Challenge: support mobility between cells connected through an IP core while satisfying real-time requirements Advanced Networking, Master Program 4

5 Problem and possible solutions Advanced Networking, Master Program 5

6 What is the problem and how to solve? TCP UDP Internet Advanced Networking, Master Program 6

7 What is the problem and how to solve? TCP UDP Internet Communication disruption should be minimized or even eliminated Advanced Networking, Master Program 7

8 What is the problem and how to solve? Routing Forwarding is based on some destination address (a locator) Change of location (due to mobility) requires change of destination address or needs an update of routing tables Ideas Specific routes to end systems (per-host forwarding) Multicast Modification of the destination address Tunneling Advanced Networking, Master Program 8

9 Specific routes to end systems Change of routing table entries to forward packets to the right destination Distribution of routing information for every mobile everywhere Internet Source BS BS BS BS Advanced Networking, Master Program 9

10 Specific routes to end systems Change of routing table entries to forward packets to the right destination Internet Source Distribution of routing information for every mobile everywhere Does not scale to a large network Security problems (routing table updates) BS BS BS BS Distribution of routing information Advanced Networking, Master Program 10

11 Multicast Building of a multicast tree Security problem Home Agent (HA) Internet Source Overhead Sending data packets to old and new locations BS BS BS BS Advanced Networking, Master Program 11

12 Modification of the destination address Adjust the host address depending on the current location Problems to find a mobile host without a constant address Changing the destination address of IP packets HA Internet Source Problems with application due to change of address Security problem BS BS BS BS Advanced Networking, Master Program 12

13 Tunneling Separation of a terminal/user identificator from a topological locator Security problem Tunnel data packets to the new location HA Internet Source Location update at HA BS BS BS BS Advanced Networking, Master Program 13

14 Tasks and criteria of mobility management Important tasks of mobility management Find and address a mobile away from home Support continuous communication after change of location Security: avoid misuse of mechanism Privacy: hide location from others Important criteria to compare mobility protocols Handover (HO) performance Delay to update the route Packet loss due to handover Protocol overhead: consumption of network resources Scalability: protocol overhead in large networks with large numbers of mobile nodes Robustness: adaptability to different network conditions and failures Ease of deployment: simplicity, suitability to different network scenarios Advanced Networking, Master Program 14

15 IP-based mobility management Advanced Networking, Master Program 15

16 IP-based mobility IP routing Forwarding is based on IP destination address; network prefix (e.g ) 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 Basic mechanisms Specific routes to end-system: per-host forwarding Distribution of routing information to every router/switch Change of multiple routing table entries upon terminal movement Does not scale well with the number of routers and mobile hosts Separation of terminal identity from location: tunneling Terminal/user identifier and topological location address High latency for updates Multicast Modification of destination address depending on current location Almost impossible to find a mobile node DNS updates take to long time TCP connections break Advanced Networking, Master Program 16

17 Mobile IP Requirements for Mobile IP Transparency Mobile end-systems keep their IP address Continuation of communication after interruption of link Point of connection to the fixed network can be changed Compatibility Support of the same layer 2 protocols as IP No changes to current end-systems and routers required Mobile end-systems can communicate with fixed systems 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 Advanced Networking, Master Program 17

18 Mobile IP 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 for the MN Care-of Address (CoA) Address of the current tunnel end-point for the MN (at FA or MN) Current location of the MN from an IP point of view Can be chosen, e.g., via DHCP Correspondent Node (CN) Communication partner Advanced Networking, Master Program 18

19 Mobile IP basics: example network HA MN Router Internet Mobile end-system Home network: physical network for the MN Router FA CN Foreign network: current physical network for the MN End-system Router Advanced Networking, Master Program 19

20 Mobile IP basics: data transfer to the mobile node HA 2 MN Internet 3 Receiver FA CN Sender 1 1. Sender sends to the IP address of MN, HA intercepts packet (proxy ARP) 2. HA tunnels packet to CoA, here FA, by encapsulation 3. FA forwards the packet to the MN Advanced Networking, Master Program 20

21 Mobile IP basics: data transfer from the mobile node HA MN Internet Sender FA CN 1. Sender sends to the IP address of the receiver as usual, FA works as default route Receiver Advanced Networking, Master Program 21

22 Mobile IP basics: agent discovery (IPv4) Agent discovery: How does the MN discover that it has moved? Agent advertisement: FAs and HAs advertise their presence periodically using special agent advertisement messages For these advertisements Internet control message protocol (ICMP) messages are used with some mobility extensions The TTL field of the IP packet is set to 1 for all advertisements to avoid forwarding them Agent solicitation: If no agent advertisements are present or the inter-arrival time is too high, and an MN has not received a COA by other means The mobile node must send agent solicitations A mobile node can send out three solicitations, one per second, as soon as it enters a new network If a node does not receive an answer to its solicitations it must decrease the rate of solicitations exponentially to avoid flooding the network until it reaches a maximum interval between solicitations (typically one minute) Advanced Networking, Master Program 22

23 Mobile IP basics: agent discovery (IPv4) Foreign network 1. Advertisement (CoA) 2. MN sends Registration Request FA advertises services 3. FA relays Binding Update to HA Home network IPv4 MN 6. FA relays reply to MN 5. HA accepts binding or denies (registration reply) HA 4. HA maintains the association between home address and current CoA and registration lifetime (binding) Here the CoA denotes the address of the FA The MN could also get it directly via DHCP (co-located care-off address) The binding update is a remote redirect and therefore needs authentication After the registration, the HA tunnels data for the MN to the CoA Advanced Networking, Master Program 23

24 Mobile IP basics: registration (IPv4) Registration (always limited lifetime!) Having received a COA, the MN has to register with the HA The main purpose of the registration is to inform the HA of the current location for correct forwarding of packets. There are two ways of registration: COA is at the FA: The MN sends its registration request containing the COA to the FA FA forwards the request to the HA HA now sets up a mobility binding containing the mobile node s home IP address and the current COA After setting up the mobility binding, the HA sends a reply message back to the FA which forwards it to the MN COA is co-located: MN sends the request directly to the HA and vice versa Advanced Networking, Master Program 24

25 Mobile IP basics: registration (IPv4) COA is at the FA COA is co-located Advanced Networking, Master Program 25

26 Mobile IP basics: tunnel end points (IPv4) HA Internet CN FA Destination is: FA FA FA Home address: CoA: 1- FA-CoA: or 2- Co-located CoA: 9.9.x.x Advanced Networking, Master Program 26

27 Mobile IP basics: tunnel end points (IPv4) HA Internet CN FA De-tunneling by MN FA FA FA Home address: CoA: 1- FA-CoA: or 2- Co-located CoA: Advanced Networking, Master Program 27

28 Tunneling Tunneling sending a packet through a tunnel, is achieved by using encapsulation Encapsulation is the mechanism of taking a packet consisting of packet header and data and putting it into the data part of a new packet. Decapsulation is the reverse operation, taking a packet out of the data part of another packet. Original IP header Original data new IP header New data Outer header Inner header Original data Advanced Networking, Master Program 28

29 Tunneling IP-in-IP encapsulation (mandatory, RFC 2003) Tunnel between HA and CoA ver. IHL TOS length IP identification flags fragment offset TTL IP-in-IP IP checksum IP address of HA Care-of address COA ver. IHL TOS length IP identification flags fragment offset TTL lay. 4 prot. IP checksum IP address of CN IP address of MN MIP header IP packet TCP/UDP/... payload Advanced Networking, Master Program 29

30 Tunneling Minimal encapsulation (optional) Avoids repetition of identical fields E.g. TTL, IHL, version, TOS Only applicable for unfragmented packets, no space left for fragment identification ver. IHL TOS length IP identification flags fragment offset TTL min. encap. IP checksum IP address of HA care-of address COA lay. 4 protoc. S reserved IP checksum IP address of MN original sender IP address (if S=1) TCP/UDP/... payload MIP header Minimized IP packet Advanced Networking, Master Program 30

31 Optimization of packet forwarding Triangular Routing Sender sends all packets via HA to MN Higher latency and network load Ideas for Solutions Sender learns the current location of MN Direct tunneling to this location HA informs a sender about the location of MN Security problems with binding updates Change of FA Packets on-the-fly during the change can be lost New FA informs old FA to avoid packet loss, old FA now forwards remaining packets to new FA This information also enables the old FA to release resources for the MN Advanced Networking, Master Program 31

32 Tunneling and route optimization (IPv4) Foreign network MN 3. FA strips off the tunnel header and relays the rest to the MN FA 5. The CN can tunnel IP packets directly to the FA 4. HA can send a binding update to CN 2. HA encapsulates the IP packet into a new IP packet by adding a tunneling header with the care-of address as destination. Tunnel source IP address is the HA address HA CN 1. CN sends IP packet to home address of MN. Initially the CN only knows the home address of the MN Home network The home agent can either use IP-within-IP or minimal encapsulation to reduce the header overhead Route optimization can be done if the HA sends a Binding Update to the CN Subsequent packets can be tunneled directly from the CN to the FA In the reverse direction normal standard IP routing mechanisms are used to deliver IP datagrams from the MN Problems if the MN moves to another FA! Advanced Networking, Master Program 32

33 Change of foreign agent (IPv4) 5. FA 2 relays to the MN FA2 8. Now the CN can again tunnel more directly to the MN CN 1. MN moves to a new subnet 4. The FA 1 tunnels the IP packets to the MN s new location (FA 2) 3. CN attempts to reach the MN using the obsolete care-of address 7. HA sends a Binding Update to the CN MN 2. MN communicates its new care-of address (of FA 2) to the previous FA FA1 6. FA 1 sends the HA a Binding Warning and asks the HA to send the CN a Binding Update HA After having moved to the new FA, the MN can also communicate its new care-of address to the previous FA Note that most of the Binding Update messages are not emitted by the MN, thus they are not going over the wireless link Problem if FA1 does not know the new care-of address of the MN FA1 must re-route the traffic to the HA, which again handles it via a new tunnel to FA2 Advanced Networking, Master Program 33

34 Change of foreign agent (IPv4) CN HA FA old FA new MN Data Data Data Update ACK Warning Request Update ACK Data Data Data Update ACK Data Data Registration Data Data MN changes location t Advanced Networking, Master Program 34

35 Reverse tunneling (RFC 3024) HA 2 MN Internet 1 Sender FA CN Receiver 3 1. MN sends to FA 2. FA tunnels packets to HA by encapsulation 3. HA forwards the packet to the receiver (standard case) Advanced Networking, Master Program 35

36 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) MIP reverse tunneling is backwards compatible The extensions can be implemented easily and cooperate with current implementations of Mobile IP without these extensions Agent advertisements can carry requests for reverse tunneling Advanced Networking, Master Program 36

37 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 auto-configuration 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) Handover 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 Advanced Networking, Master Program 37

38 Changes with IPv6 Huge address space with IPv6 address renumbering scheme Better mobility support Mobile IP was designed as add-on to IPv4 Majority of IPv4 nodes do not support Mobile IP MN can use Address Autoconfiguration which eliminates the need of a Foreign Agent Stateless: to configure its care-of address from a NW prefix of the foreign NW and a MN interface identifier. The needed information is published by neighboring routers through the Neighbor Discovery protocol in the foreign network (combined ARP/ICMP) Statefull: by using a centralized DHCP server Source Routing: Instead of tunneling packets using IP in IP, IPv6 Routing Headers are used Every IPv6 node will have implemented IPv6 authentication headers to be used with binding updates Advanced Networking, Master Program 38

39 Tunneling operation (IPv6) Foreign network 5. The CN afterwards can send packets directly to the CN by using Routing headers CN MN 3. Strips off the tunnel header and reads the packet 4. The MN sees that the packet was routed through the HA and therefore can send a binding update to the CN directly 2. HA encapsulates the IP packet into a new IP packet by adding a tunneling header with the care-of address as destination. Tunnel source IP address is the HA address HA 1. CN sends IP packet to home address of MN Home network Route optimization: only the MN can send a binding update, e.g. to the CN. If the CN knows the care-of address of the MN it can prevent triangle routing through the HA Tunneling is facilitated using routing headers and not IPv6 in IPv6 No problems if the MN moves to another FA, as IPv6 requires that binding messages have to be send by the MN to the CN and HA directly every time the MN moves IPv6 uses destination option headers to include the binding update in a normal IPv6 packet Advanced Networking, Master Program 39

40 Moving to a new location (IPv6) New Foreign network 3. The CN again can send packets directly to the CN by using IPv6 Routing headers CN 2. MN also sends a Binding Update directly to the CN MN 1. MN sends a Binding Update directly to the HA HA All Binding Update messages intended for the CN are transmitted directly by the MN. This becomes feasible as IPv6 uses destination option headers to include the binding update in a normal IPv6 packet, e.g. in TCP ACK messages Thus corresponding nodes are generally kept updated and can send nearly every packet directly to the MN Advanced Networking, Master Program 40

41 Problems of Mobile IP Security and Privacy Authentication with FA problematic where the FA belongs to another organization No protocol for key management and key distribution has been standardized in the Internet (manual key distribution) Combination with IPsec is problematic (tunnel within tunnel) No location privacy Firewalls QoS Typically Mobile IP cannot be used together with firewalls, special set-ups are needed (such as reverse tunneling) QoS needs to go in line with mobility support (handover requires update of location information as well as QoS information) Security, firewalls, QoS etc. are topics of current research and discussions! Advanced Networking, Master Program 41

42 Dynamic Host Configuration Protocol (DHCP) Application Simplification of installation and maintenance of networked computers Supplies systems with all necessary information, such as IP address, DNS server address, domain name, subnet mask, default router etc. Enables automatic integration of systems into an Intranet or the Internet Can be used to acquire a CoA for Mobile IP (co-location of MN and FA) Client/Server-Model The client sends via a MAC broadcast a request to the DHCP server (might be via a DHCP relay) DHCPDISCOVER DHCPDISCOVER DHCP server client client relay Advanced Networking, Master Program 42

43 DHCP protocol mechanisms Server (not selected) Client Server (selected) Initialization Determine the configuration DHCPDISCOVER DHCPDISCOVER Determine the configuration DHCPOFFER DHCPOFFER Collection of replies Selection of configuration DHCPREQUEST (Reject) DHCPREQUEST (Options) DHCPACK Confirmation of configuration Initialization completed Release DHCPRELEASE Delete context Advanced Networking, Master Program 43

44 DHCP characteristics Server Several servers can be configured for DHCP, coordination not yet standardized (i.e. manual configuration) Renewal of configurations IP addresses have to be requested periodically, simplified protocol Options (RFC 2132) Available for routers, subnet mask, NTP (network time protocol) timeserver, SLP (service location protocol) directory, DNS (domain name system) Big security problems! No authentication of DHCP information specified Advanced Networking, Master Program 44

45 References Books and Presentations Jochen Schiller: Mobile Communications (German and English), Addison- Wesley, 2000 (chapter 9 provides an overview on Mobile IP) Charles Perkins: Mobile IP Design Principles and Practises. Addisson Wesley, 1998 Ramjee Prasad, Marina Ruggieri: Technology Trends in Wireless Communications, Artech House, 2003 Wisely, Eardley, Burness: IP for 3G: Networking Technologies for Mobile Communications, Wiley, 2002 (chapter 5 provides classification of mobility mechanisms and overview on protocols, including session-layer mobility) Important standards: Mobile IP: RFC 3220, formerly: RFC 2002 Reverse tunneling: RFC 3024, formerly: 2344 DHCP: RFC 2131, RFC 2132 ICMP: RFC 1256 Advanced Networking, Master Program 45

46 Contact Integrated Communication Systems Group Ilmenau University of Technology Univ.-Prof. Dr.-Ing. Andreas Mitschele-Thiel fon: +49 (0) Visitors address: Technische Universität Ilmenau Helmholtzplatz Zuse Building Room 1032 D Ilmenau Integrated Communication Systems Group Ilmenau University of Technology