Multimedia Network Lab. Mobile Computing Chapter 8: Mobile Network Layer Prof. Sang-Jo Yoo http://multinet.inha.ac.kr The Graduate School of Information Technology and Telecommunications, INHA University http://multinet.inha.ac.kr Multimedia Network Lab. Contents Mobile IP overview Agent discovery Registration Tunneling DHCP Mobile IP multicasting The Graduate School of Information Technology and Telecommunications, INHA University 2 http://multinet.inha.ac.kr Multimedia Network Lab. Motivation for Mobile IP Routing based on IP destination address, network prefix (e.g. 129.13.42) determines physical subnet To avoid an explosion of routing tables, only prefixes are stored aand further optimizations are applied. 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 Specific routes to end-systems? 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, security problems The Graduate School of Information Technology and Telecommunications, INHA University 3 http://multinet.inha.ac.kr Multimedia Network Lab. Motivation for Mobile IP Changing the IP-address? adjust the host IP address depending on the current location Assigning a new IP address (DHCP) Problem: nobody knows about this new address. Almost impossible to find a mobile system, DNS updates take to long time TCP connections break, security problems TCP connection = {source IP, source port, destination IP, destination port} TCP connection cannot survive any address change. The Graduate School of Information Technology and Telecommunications, INHA University 4 http://multinet.inha.ac.kr Multimedia Network Lab. Requirements to Mobile IP Transparency Mobility should remain ‘invisible’ for many higher layer protocols and applications For TCP, mobile computer must keep its IP address. 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 The minimum requirement: all the messages related to the management of Mobile IP are authenticated. Efficiency and scalability Only little additional messages to the mobile system required (connection typically via a low bandwidth radio link) The Graduate School of Information Technology and Telecommunications, INHA University 5 http://multinet.inha.ac.kr Multimedia Network Lab. 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 Correspondent Node (CN) communication partner The Graduate School of Information Technology and Telecommunications, INHA University 6 http://multinet.inha.ac.kr Multimedia Network Lab. Terminology Care-of Address (COA) Foreign agent COA The COA could be located at the FA (IP address of FA) The FA is the tunnel end-point and forwards packets to the MN. Many MN using the FA can share this COA. Co-located COA MN temporarily acquired an additional IP address which acts as COA. Tunnel end-point is at the MN. Co-located care-of address can be acquired using services such as DHCP The Graduate School of Information Technology and Telecommunications, INHA University 7 http://multinet.inha.ac.kr Multimedia Network Lab. Example network HA MN router home network mobile end-system Internet (physical home network for the MN) FA foreign network router (current physical network for the MN) CN end-system router The Graduate School of Information Technology and Telecommunications, INHA University 8 http://multinet.inha.ac.kr Multimedia Network Lab. Data transfer to the mobile system HA 2 MN home network 3 receiver Internet FA foreign network 1. Sender sends to the IP address of MN, 1 HA intercepts packet (proxy ARP) CN 2. HA tunnels packet to COA, here FA, by encapsulation 3. FA forwards the packet sender to the MN The Graduate School of Information Technology and Telecommunications, INHA University 9 http://multinet.inha.ac.kr Multimedia Network Lab. Data transfer from the mobile system HA 1 MN home network sender Internet FA foreign network 1. Sender sends to the IP address CN of the receiver as usual, FA works as default router receiver The Graduate School of Information Technology and Telecommunications, INHA University 10 http://multinet.inha.ac.kr Multimedia Network Lab. Overview COA router home router MN network HA FA foreign Internet network CN router 3. home router router 2. MN network HA FA 4. foreign Internet network 1. CN router The Graduate School of Information Technology and Telecommunications, INHA University 11 http://multinet.inha.ac.kr Multimedia Network Lab. Mobile IP Design Goals A mobile node must be able to communicate with other nodes after changing it’s link-layer attachment, yet without changing its IP address A mobile node must be able to communicate with other nodes that do not implement mobile IP Mobile IP must use authentication to offer security against redirectment attacks The number of administrative messages should be small to save bandwidth & power Mobile IP must impose no additional constraints on the assignment of IP addresses The Graduate School of Information Technology and Telecommunications, INHA University 12 http://multinet.inha.ac.kr Multimedia Network Lab. Protocol Overview Advertisement 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 MN reads a COA from the FA advertisement messages A mobile node can solicit for mobility agents Registration - when a mobile node is away from home, it must register its care-of address with it’s home agent these actions have to be secured by authentication Delivering Datagrams Datagrams must be forwarded by the Home Agent to the Foreign Agent for delivery to the care-of address. The delivery mechanism must handle all packets (including broadcast and multicast) A tunnel is used for this The Graduate School of Information Technology and Telecommunications, INHA University 13 http://multinet.inha.ac.kr Multimedia Network Lab. Overall Behaviors The Graduate School of Information Technology and Telecommunications, INHA University 14 http://multinet.inha.ac.kr Multimedia Network Lab. 1. Agent Discovery Problems: How to find a foreign agent? How does the MN discover that it has moved? Æ Agent advertisement and Agent solicitation Agent advertisement HA and FA advertise their presence periodically using Agent advertisement messages ICMP (Internet Control Message Protocol) message with some mobility extensions : RFC 1256 IP header: TTL=1 destination IP: 224.0.0.1 (multicasting), 255.255.255.255(broadcasting) The Graduate School of Information Technology and Telecommunications, INHA University 15 http://multinet.inha.ac.kr Multimedia Network Lab. Agent advertisement 0 7 8 15 1623 24 31 Type=9 Code checksum #addresses addr. size lifetime router address 1 preference level 1 router address 2 type = 16 preference level 2 length = 6 + 4 * #COAs . Lifetime: max lifetime in seconds a node can request R: registration required type = 16 length sequence number B: busy, no more registrations registration lifetime R B H F M G r T reserved H: home agent COA 1 COA 2 F: foreign agent M: minimal encapsulation . G: GRE encapsulation r: =0, ignored (former Van Jacobson compression) T: FA supports reverse tunneling reserved: =0, ignored The Graduate School of Information Technology and Telecommunications, INHA University 16 http://multinet.inha.ac.kr Multimedia Network Lab. Agent Solicitation MN can send Agent solicitation message If no agent advertisement are present, The inter-arrival time of agent advertisements is too high, or The MN just power on. Based on RFC 1256, ICMP router solicitation message Move detection Move detection using lifetime If a MN fails to hear an advertisement from the foreign agent (or home agent) with the specified Lifetime. The MN can assume that it has moved to a different link, waits Agent Advertisement or sends Agent Solicitation. Move detection using network-prefixes If the network-prefix of the received Agent Advertisement is different from the that of the previous foreign agent, then registration process should be invoked. The Graduate School of Information Technology and Telecommunications, INHA University 17 http://multinet.inha.ac.kr Multimedia Network Lab. 2. Registration Request forwarding services when visiting a foreign network This allocates a local (foreign) node address Inform home agent of their current care-of address This creates a binding of the foreign node address to the home address Renew a binding that’s about to expire Bindings have lifetimes De-register when they return home The Graduate School of Information Technology and Telecommunications, INHA University 18 http://multinet.inha.ac.kr Multimedia Network Lab. Registration and Security The home node and the mobile node have conducted some form of prior key exchange This defines a “secret” between the two nodes The authentication mechanism must defend against replay attacks A replay attack occurs when a 3rd party can capture your packets and then “replay” them, fooling you into thinking they are correctly authenticated. E.g., sending an encrypted password over a network leaves you open to a replay attack. Note that attack didn’t decrypt. Nonces: Each message from A -> B includes a new random number. When B replies to A, it must include that same random number. Likewise, each B->A message includes a new random number generated by B and echoed by A.