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Wireless & Mobile Communications Chapter 6: Network Protocols/Mobile IP

Wireless & Mobile Communications Chapter 6: Network Protocols/Mobile IP. Motivation Data transfer Encapsulation Security IPv6. Problems DHCP Ad-hoc networks Routing protocols. Why Mobile IP?. What do cellular networks and wireless LANs provide? Wireless connectivity

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Wireless & Mobile Communications Chapter 6: Network Protocols/Mobile IP

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  1. Wireless & Mobile Communications Chapter 6: Network Protocols/Mobile IP Motivation Data transfer Encapsulation Security IPv6 • Problems • DHCP • Ad-hoc networks • Routing protocols

  2. Why Mobile IP? • What do cellular networks and wireless LANs provide? • Wireless connectivity • Mobility at the data link layer • What is Dynamic Host Configuration Protocol (DHCP)? • It provides local IP addresses for mobile hosts • Is not secure • Does not maintain network connectivity when moving around • What they do not provide: • Transparent connectivity at the network layer • Mobility with local access • The difference between mobility and nomadicity! ICS 243E - Ch 6 Net. Protocols

  3. What is Mobile IP? • Mobile IP provides network layer mobility • Provides seamless roaming • ‘‘Extends’’ the home network over the entire Internet ICS 243E - Ch 6 Net. Protocols

  4. IP Overview 1/3 • IP Addressing : • Dotted Decimal Notation: 32 bits (4x8) used to represent IPv4 addresses - 192.19.241.18 • Network Prefix and Host Portions: p - prefix, h - host, p + h = 32. If p = 24 then h = 32 - 24 = 8. Using above address the network prefix will be 192.19.241 and host will be 18. For those of you familiar with subnet masks, “p” represents the number of 1’s in the subnet mask. If p = 24, subnet mask is 255.255.255.0, if p = 26, subnet mask is 255.255.255.192. ICS 243E - Ch 6 Net. Protocols

  5. IP Overview 2/3 • IP Routing: • Network prefix is used for routing. Routing tables are used to look up next hop and the interface on the router that is to be used. • In the routing tables we use the following notation: target/prefix length, e.g., 192.19.241.0/24, or 192.19.241.192/26. • If two subnet masks/prefixes fit the address, the one with the largest prefix is chosen for routing. E.g., a router with the following 3 entries in its table: 7.7.7.99/32 (p=32 host specific) and 7.7.7.0/24 (0<p<32 network prefix) and 0.0.0.0/0 (p=0 default) will use entry 2 for an IP packet with destination 7.7.7.1 and entry 3 for destination 192.33.14.12. ICS 243E - Ch 6 Net. Protocols

  6. IP Overview 3/3 • Domain Name System (DNS): used to translate a host name to an IP address. A host sends a query to a server to obtain the IP address of a destination of which it only has the host name. • Link Layer Addresses - Address Resolution Protocol (ARP): • Once a host has the IP address of a destination it then needs to finds its layer 2 address or the layer 2 address of the next hop on the path. A broadcast message is sent and the targeted host responds with its layer 2 address. • A proxy ARP is a response by a node for another node that cannot respond at the time the request is made (e.g. the node is a mobiel node and not on its host net at the time, its home agent will respond in its stead). • A gratuitous ARP, is a reply to no ARP request, used by a node that just joins the network and wants to make its address known. Can be used by a mobile node upon its return to its home net. ICS 243E - Ch 6 Net. Protocols

  7. Motivation for Mobile IP • IP Routing • based on IP destination address, network prefix (e.g. 129.13.42) determines physical subnet • change of physical subnet implies change of IP address to have a topologically correct address (standard IP) or needs special entries in the routing tables • Specific routes to end-systems? • requires changing 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, security problems • Changing the IP-address? • adjust the host IP address depending on the current location • almost impossible to find a mobile system, DNS updates take long time • TCP connections break, security problems ICS 243E - Ch 6 Net. Protocols

  8. What Mobile IP does: • Mobile IP solves the following problems: • if a node moves without changing its IP address it will be unable to receive its packets, • if a node changes its IP address it will have to terminate and restart its ongoing connections everytime it moves to a new network area (new network prefix). • Mobile IP is a routing protocol with a very specific purpose. • Mobile IP is a network layer solution to node mobility in the Internet. • Mobile IP is not a complete solution to mobility, changes to the transport protocols need to be made for a better solution (i.e., the transport layers are unaware of the mobile node’s point of attachment and it might be useful if, e.g., TCP knew that a wireless link was being used!). ICS 243E - Ch 6 Net. Protocols

  9. Requirements to Mobile IP (RFC 2002) • 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 • 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 ICS 243E - Ch 6 Net. Protocols

  10. 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) • actual location of the MN from an IP point of view • can be chosen, e.g., via DHCP • Correspondent Node (CN) • communication partner ICS 243E - Ch 6 Net. Protocols

  11. Mobile IP Operation: Summary • Consists of 3 steps: • Agent discovery, • Registration, and • Routing/Tunneling ICS 243E - Ch 6 Net. Protocols

  12. Operation Summary 1/3 • Agent Advertisement/Discovery: consists of broadcast messages used by mobiles to detect that they have moved and are required to register with a new FA. • FAs send agent advertisements • MNs can solicit for agents if they have not heard an agent advertisement in awhile or use some other mechanism to obtain a COA or temp. IP address (e.g. DHCP). • MNs know they are home when they recognize their HA. ICS 243E - Ch 6 Net. Protocols

  13. Operation Summary 2/3 • Registration: used by a MN to inform the FA that it is visiting. • The new care of address of the MN is sent to the HA. • Registration expires, duration is negotiated during registration • Mobile must re-register before it expires • All registrations are authenticated • The MN sends a regristration request in to the FA which passes it along to the home agent. The HA responds to the FA which then informs the MN that all is in order and registration is complete. ICS 243E - Ch 6 Net. Protocols

  14. Operation Summary 3/3 • Routing/Encapsulation/Tunneling: consists of the delivery of the packets to the mobile node at its current care of address. • Sender does not need to know that the destination is a MN. • HA intercepts all packets for the MN and passes them along to MN using a tunnel. • MN communicates directly with the CN. • Referred to as Triangle Routing ICS 243E - Ch 6 Net. Protocols

  15. Example network HA MN Internet router home network mobile end-system (physical home network for the MN) FA foreign network router (current physical network for the MN) CN end-system router ICS 243E - Ch 6 Net. Protocols

  16. Data transfer to the mobile system HA 2 MN Internet home network 3 receiver foreign network FA 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 1 CN sender ICS 243E - Ch 6 Net. Protocols

  17. Data transfer from the mobile system HA 1 MN Internet home network sender FA foreignnetwork 1. Sender sends to the IP address of the receiver as usual, FA works as default router CN receiver ICS 243E - Ch 6 Net. Protocols

  18. Overview COA foreign network router FA MN home network router HA Internet CN router foreign network 3. router FA MN home network router HA 2. 4. Internet 1. CN router ICS 243E - Ch 6 Net. Protocols

  19. Network integration • Agent Advertisement Discovery • HA and FA periodically send advertisement messages into their physical subnets • MN listens to these messages and detects, if it is in the home or a foreign network (standard case for home network) • MN reads a COA from the FA advertisement messages • Registration (always limited lifetime!) • MN signals COA to the HA via the FA, HA acknowledges via FA to MN • these actions have to be secured by authentication • Routing/Encapsulation/Tunneling • HA advertises the IP address of the MN (as for fixed systems), i.e. standard routing information • packets to the MN are sent to the HA, • independent of changes in COA/FA ICS 243E - Ch 6 Net. Protocols

  20. R B H F M G V Agent advertisement 0 7 8 15 16 23 24 31 type code checksum #addresses addr. size lifetime router address 1 preference level 1 router address 2 preference level 2 . . . type length sequence number registration lifetime reserved COA 1 COA 2 . . . ICS 243E - Ch 6 Net. Protocols

  21. Registration MN FA HA MN HA registration request registration request registration request registration reply registration reply t registration reply t ICS 243E - Ch 6 Net. Protocols

  22. S B D M G V Mobile IP registration request 0 7 8 15 16 23 24 31 type rsv lifetime home address home agent COA identification extensions . . . ICS 243E - Ch 6 Net. Protocols

  23. Processing Registration Messages 1/3 • A MN, depending on which registration scenario it is in, will figure what addresses to use in the various fields of the Registration request message. • Link layeraddresses are tricky: • A MN may not use ARP if it is using a FA COA. It needs to use the address of the FA as the destination address. • If it is using a collocated COA, then it uses ARP to locate the default router using its COA as source. Note that if the ‘R’ bit is set is uses the FA address as the destination address. • For de-registration is uses ARP to locate the HA link address and it uses its own home address for the ARP message. • For network layer addresses (i.e., IP addresses): • It uses the FA address as destination address when using the FA COA and its own home address as the source address. • If using a collocated COA it uses itsCOA as source address and the HAaddress as destination address. Note that if the ‘R’ bit is set then is must use the same addresses as for the FA COA scenario. • For de-registration it uses its own home address as source and the HA address as destination. ICS 243E - Ch 6 Net. Protocols

  24. Processing Registration Messages 2/3 • For the FA: • A FA may refuse a Registration request for a number of reasons: lifetime too long, authentication failed, requested tunneling not supported, cannot handle another MN (current load too high). • If an FA does not refuse the request it relays it to the HA. Relaying is different from forwading as the FA is required to process the packet and create new headers. • Some important fields of the request message are recorded for use later on: MN link layer address, MN IP address, UDP source port, HA IP address, identification number and requested lifetime. • Regarding a Registration reply message, the FA can refuse it and send a decline to the MN is it finds the reply from the HA to be invalid. Otherwise it updates its list of visiting MNs and begins acting on behalf of the MN. ICS 243E - Ch 6 Net. Protocols

  25. Processing Registration Messages 3/3 • For a HA • The HA will determine, as the FA did, whether it will accept the request. If it does not it returns a code in the reply message indicating the cause of the failed request. • If the request is accepted, the reply is sent back by reversing all the IP addresses and UDP port numbers. • The HA updates the binding table corresponding to that MN dependent upon the nature of the request. ICS 243E - Ch 6 Net. Protocols

  26. Routing/Tunneling 1/5 • Routing a packet to a MN involves the following: • A router on the home link, possibly the HA, advertisesreachability to the network prefix of the MN’s home address. • All packets are therefore routed to the MN’s home link. • A HA intercepts the packets for the MN and tunnels a copy to each COA in the binding table. • At the foreign link either the MN extracts the packet (collocated COA) or the FA extracts the packet and forwards it to the MN. ICS 243E - Ch 6 Net. Protocols

  27. Routing/Tunneling 2/5 • A HA can use one of two methods to intercept a MN’s packets: • The HA is a router with multiple network interfaces. In that case it advertises reachability to the MN’s home network prefix. • The HA is not a router with multiple intefaces. It must use ARP to receive the MN’s packets. It either responds to ARP requests on behalf of the MN (proxy ARP) or uses gratuitous ARPs to inform the home network that it is receiving the MN’s IP packets. This is to update any ARP caches that hosts and other devices might have. ICS 243E - Ch 6 Net. Protocols

  28. Routing/Tunneling 3/5 • How to ‘fool’ the routing table into handling tunneled packets at the HA? • A virtual interface is used to do the encapsulation. • A packet destined for the MN is handled by the routing routine as all received IP packets are. • The routing table has a host specific entry for the MN. This host specific entry is used to route the packet to a virtual interface that basically consists of a process that does encapsulation. • Once encapsulation has been performed the packet is sent to be processed by the routing routine again. This time the destination address is the COA and it is routed normally. ICS 243E - Ch 6 Net. Protocols

  29. Routing/Tunneling 4/5 • How to ‘fool’ the routing table into handling tunneled packets at the FA? • The same procedure is used as above. • A packet coming in with a COA that is one of the FA addresses’ is handled by the routing routine. • A host specific address (its own address) in the routing table points to the higher layers and the packet is passed on to a virtual interface. • The virtual interface consists of a process that decapsulates the packet and re-routes it to the routing routine. • The routing routine routes the packet normally based upon a host specific entry that is the MN’s home address (for which it has the link layer address!). ICS 243E - Ch 6 Net. Protocols

  30. Routing/Tunneling 5/5 • How does a MN route its packets? • It needs to find a router to send all its packets to. • It can select a router in one of a number of ways dependent upon whether it has a FA COA or a collocated COA. • Having a FA COA does not imply that the MN needs to use it as its default router for sending packets. It can use any router that sends advertisements or that is advertised in the Agent Advertisement message. • If the MN is using a collocated COA it needs to listen for router advertisements or is it hears none, use DHCP to find the default router. • Determining the link layer address is another issue. Collocated COA MNs can use ARP. FA COA must note the link layer address when they receive router advertisements or agent advertisements. ICS 243E - Ch 6 Net. Protocols

  31. Encapsulation Process original IP header original data new IP header new data outer header inner header original data ICS 243E - Ch 6 Net. Protocols

  32. Types of Encapsulation • Three types of encapsulation protocols are specified for Mobile IP: • IP-in-IP encapsulation: required to be supported. Full IP header added to the original IP packet. The new header contains HA address as source and Care of Address as destination. • Minimal encapsulation: optional. Requires less overhead but requires changes to the original header. Destination address is changed to Care of Address and Source IP address is maintained as is. • Generic Routing Encapsulation (GRE):optional. Allows packets of a different protocol suite to be encapsulated by another protocol suite. • Type of tunneling/encapsulation supported is indicated in registration. ICS 243E - Ch 6 Net. Protocols

  33. IP in IP Encapsulation • IP in IP encapsulation (mandatory in 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 TCP/UDP/ ... payload ICS 243E - Ch 6 Net. Protocols

  34. Minimum Encapsulation • 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 ICS 243E - Ch 6 Net. Protocols

  35. original header original data outer header GRE header originalheader original data ver. IHL TOS length IP identification flags fragment offset TTL GRE IP checksum new header new data IP address of HA Care-of address COA C R K S s rec. rsv. ver. protocol checksum (optional) offset (optional) key (optional) sequence number (optional) routing (optional) ver. IHL TOS length IP identification flags fragment offset TTL lay. 4 prot. IP checksum IP address of CN IP address of MN TCP/UDP/ ... payload Generic Routing Encapsulation ICS 243E - Ch 6 Net. Protocols

  36. Routing techniques • Triangle Routing: tunneling in its simplest form has all packets go to home network (HA) and then sent to MN via a tunnel. • This involves two IP routes that need to be set-up, one original and the second the tunnel route. • Causes unnecessary network overhead and adds to the latency. • Route optimization: allows the correstpondent node to learn the current location of the MN and tunnel its own packets directly. Problems arise with • mobility: correspondent node has to update/maintain its cache. • authentication: HA has to communicate with the correspondent node to do authentication, i.e., security association is with HA not with MN. ICS 243E - Ch 6 Net. Protocols

  37. Optimization of packet forwarding • 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 ICS 243E - Ch 6 Net. Protocols

  38. Change of foreign agent CN HA FAold FAnew MN request update ACK data data MN changeslocation registration registration update ACK data data data warning update ACK data data t ICS 243E - Ch 6 Net. Protocols

  39. Problems with Triangle Routing • Triangle routing has the MN correspond directly with the CN using its home address as the SA • Firewalls at the foreign network may not allow that • Multicasting: if a MN is to participate in a multicast group, it needs to use a reverse tunnel to maintain its association with the home network. • TTL: a MN might have a TTL that is suitable for communication when it is in its HM. This TTL may not be sufficient when moving around (longer routes possibly). When using a reverse tunnel, it only counts as a single hop. A MN does not want to change the TTL everytime it moves. • Solution: reverse tunneling ICS 243E - Ch 6 Net. Protocols

  40. Reverse tunneling (RFC 2344) HA 2 MN Internet home network 1 sender FA foreignnetwork 1. MN sends to FA 2. FA tunnels packets to HA by encapsulation 3. HA forwards the packet to the receiver (standard case) 3 CN receiver ICS 243E - Ch 6 Net. Protocols

  41. Mobile IP with reverse tunneling • Routers accept often only “topologically correct“ addresses (firewall!) • a packet from the MN encapsulated by the FA is now topologically correct • Multicast and TTL problems solved • Reverse tunneling does not solve • all 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 (longer routes) • The new standard is backwards compatible • the extensions can be implemented easily ICS 243E - Ch 6 Net. Protocols

  42. 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 • 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 ICS 243E - Ch 6 Net. Protocols

  43. 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! ICS 243E - Ch 6 Net. Protocols

  44. 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 ICS 243E - Ch 6 Net. Protocols

  45. IP-Header IP header Authentification-Header authentication header UDP/TCP-Paket UDP/TCP data not encrypted encrypted IP security architecture 1/2 • Two or more partners have to negotiate security mechanisms to setup a security association • typically, all partners choose the same parameters and mechanisms • Two headers have been defined for securing IP packets: • Authentication-Header • guarantees integrity and authenticity of IP packets • if asymmetric encryption schemes are used, non-repudiation can also be guaranteed • Encapsulation Security Payload • protects confidentiality between communication partners IP header ESP header encrypted data ICS 243E - Ch 6 Net. Protocols

  46. IP security architecture 2/2 • Mobile Security Association for registrations • parameters for the mobile host (MH), home agent (HA), and foreign agent (FA) • Extensions of the IP security architecture • extended authentication of registration • prevention of replays of registrations • time stamps: 32 bit time stamps + 32 bit random number • responses: 32 bit random number (MH) + 32 bit random number (HA) MH-FA authentication FA-HA authentication MH-HA authentication registration request MH FA registration request HA registration reply registration reply ICS 243E - Ch 6 Net. Protocols

  47. Key distribution • Home agent distributes session keys • foreign agent has a security association with the home agent • mobile host registers a new binding at the home agent • home agent answers with a new session key for foreign agent and mobile node FA MH response: EHA-FA {session key} EHA-MH {session key} HA ICS 243E - Ch 6 Net. Protocols

  48. DHCP: Dynamic Host Configuration Protocol • 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 • Client/Server-Model • the client sends via a MAC broadcast a request to the DHCP server (might be via a DHCP relay) DHCPDISCOVER DHCPDISCOVER server client client relay ICS 243E - Ch 6 Net. Protocols

  49. DHCP - protocol mechanisms client server (not selected) server (selected) initialization DHCPDISCOVER DHCPDISCOVER determine the configuration determine the configuration DHCPOFFER DHCPOFFER collection of replies selection of configuration time DHCPREQUEST(reject) DHCPREQUEST(options) confirmation of configuration DHCPACK initialization completed release DHCPRELEASE delete context ICS 243E - Ch 6 Net. Protocols

  50. 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 • 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 ICS 243E - Ch 6 Net. Protocols

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