Session: 14S. K. Nayak14.1 Mobile Computing Session 14 Mobile IP S. K. Nayak Synergy, Dhenkanal

Session: 14S. K. Nayak14.2 Effect of Mobility on Protocol Stack Application: new applications and adaptations Transport: congestion and flow control Network: addressing and routing Link: media access and handoff Physical: transmission errors and interference

Session: 14S. K. Nayak14.3 Routing and Mobility Finding a path from a source to a destination Issues –Frequent route changes –Route changes may be related to host movement –Low bandwidth links

Session: 14S. K. Nayak14.4 Routing and Mobility (contd) Goal of routing protocols –decrease routing-related overhead –find short routes –find “stable” routes (despite mobility)

Session: 14S. K. Nayak14.5 Mobile IP (RFC 3344): Motivation Traditional routing –based on IP address; network prefix determines the subnet –change of physical subnet implies change of IP address (conform to new subnet), or special routing table entries to forward packets to new subnet

Session: 14S. K. Nayak14.6 Mobile IP motivation Changing of IP address –DNS updates take to long time –TCP connections break –security problems Changing entries in routing tables –does not scale with the number of mobile hosts and frequent changes in the location –security problems

Session: 14S. K. Nayak14.7 Mobile IP requirements Solution requirements –retain same IP address –use same layer 2 protocols –authentication of registration messages, …

Session: 14S. K. Nayak14.8 Mobile IP: Basic Idea Router 1 Router 3 Router 2 S MN Home agent Source: Vaidya

Session: 14S. K. Nayak14.9 Mobile IP: Basic Idea Router 1 Router 3 Router 2 SMN Home agent Foreign agent move Packets are tunneled using IP in IP Source: Vaidya

Session: 14S. K. Nayak14.10 Mobile IP: Terminology Mobile Node (MN) –node that moves across networks without changing its IP address Correspondent Node (CN) –host with which MN is “corresponding” (TCP) Home Agent (HA) –host in the home network of the MN, typically a router –registers the location of the MN, tunnels IP packets to the COA

Session: 14S. K. Nayak14.11 Terminology (contd.) Foreign Agent (FA) –host in the current foreign network of the MN, typically a router –forwards tunneled packets to the MN, typically the default router for 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

Session: 14S. K. Nayak14.12 Data transfer to the mobile system Internet sender FA HA MN home network foreign network receiver Sender sends to the IP addr 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 Source: Schiller CN

Session: 14S. K. Nayak14.13 Data transfer from the mobile system Internet receiver FA HA MN home network foreign network sender 1 1. Sender sends to the IP address of the receiver as usual, FA works as default router Source: Schiller CN

Session: 14S. K. Nayak14.14 Mobile IP: Basic Operation Agent Advertisement MN Registration HA Proxy Packet Tunneling

Session: 14S. K. Nayak14.15 Agent Advertisement HA/FA periodically send advertisement messages into their physical subnets MN listens to these messages and detects, if it is in home/foreign network MN reads a COA from the FA advertisement messages

Session: 14S. K. Nayak14.16 Agent advertisement preference level 1 router address 1 #addresses type addr. sizelifetime checksum COA 1 COA 2 typesequence numberlength code preference level 2 router address 2... registration lifetime... RBHFMGV reserved

Session: 14S. K. Nayak14.17 MN Registration MN signals COA to the HA via the FA HA acknowledges via FA to MN limited lifetime, need to be secured by authentication

Session: 14S. K. Nayak14.18 Registration t MN HA registration request registration reply t MN FAHA registration request registration request registration reply registration reply

Session: 14S. K. Nayak14.19 Registration request home agent home address typelifetime rsv identification COA extensions... SBDMGV

Session: 14S. K. Nayak14.20 HA Proxy and Tunneling HA Proxy –HA advertises the IP address of the MN (as for fixed systems) –packets to the MN are sent to the HA –independent of changes in COA/FA Packet Tunneling –HA to MN via FA

Session: 14S. K. Nayak14.21 Encapsulation original IP headeroriginal data new datanew IP header outer headerinner headeroriginal data

Session: 14S. K. Nayak14.22 IP-in-IP encapsulation IP-in-IP-encapsulation (mandatory in RFC 2003) –tunnel between HA and COA Care-of address COA IP address of HA TTL IP identification IP-in-IPIP checksum flagsfragment offset lengthTOSver.IHL IP address of MN IP address of CN TTL IP identification lay. 4 prot.IP checksum flagsfragment offset lengthTOSver.IHL TCP/UDP/... payload

Session: 14S. K. Nayak14.23 IP header fields Source and Destination addresses are those of the tunnel end points Internet header length : –Length of outer header in 32 bit words Total length : –Measures length of entire encapsulated IP datagram Don’t fragment bit : –Copied from inner header if set Time to live TTL: –Appr time to deliver to tunnel exit

Session: 14S. K. Nayak14.24 Routing failures If IP source addr of datagram matches that of the receiving router itself, then discard packet If IP source addr matches that of the tunnel exit point, then discard packet

Session: 14S. K. Nayak14.25 ICMP messages from the tunnel Encapsulator may receive ICMP messages from any intermediate router in the tunnel other than exit Network unreachable: –Return dest unreachable message to org sender Host unreachable: –Return host unreachable message Datagram too big: –Relay ICMP datagram too big to org sender

Session: 14S. K. Nayak14.26 ICMP error messages (contd.) Source route failed: –Handled by encapsulator itself and MUST NOT relay message to orginal sender Source quench: –SHOULD NOT relay message to original sender, SHOULD activate congestion control mechanism Time exceeded: –MUST be reported to original sender as host unreachable message

Session: 14S. K. Nayak14.27 Tunnel management ICMP requires routers to return 8 bytes of datagram beyond IP header –This may not contain the original datagram So not always possible for encapsulator to relay ICMP messages from interior of tunnel to original sender

Session: 14S. K. Nayak14.28 Tunnel soft state Encapsulator maintains “soft state” about tunnel –MTU of the tunnel –TTL (path length) of tunnel –Reachability of the tunnel Encapsulator updates soft state based on ICMP messages received

Session: 14S. K. Nayak14.29 Tunnel management (example) If TTL of received packet is less than the TTL value in soft state, then return error message to sender If size of received datagram is bigger than MTU of tunnel and if “don’t fragment” bit set, then return datagram too big message to sender

Session: 14S. K. Nayak14.30 Mobile IP: Other Issues Reverse Tunneling –firewalls permit only “topological correct“ addresses Optimizations –Triangular Routing: HA informs sender the current location of MN –Change of FA: new FA informs old FA to avoid packet loss

Session: 14S. K. Nayak14.31 Reverse tunneling (RFC 3024) Internet receiver FA HA MN home network foreign network sender MN sends to FA 2. FA tunnels packets to HA by encapsulation 3. HA forwards the packet to the receiver (standard case) CN

Session: 14S. K. Nayak14.32 Mobile IP: 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 too far away from the receiver)

Session: 14S. K. Nayak14.33 Reverse tunneling 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)

Session: 14S. K. Nayak14.34 Optimization of forwarding Triangular Routing –sender sends all packets via HA to MN –higher latency and network load “Solutions” –sender learns the current location of MN –direct tunneling to this location –HA informs a sender about the location of MN

Session: 14S. K. Nayak14.35 Binding Registration: When node acquires a new care-of address Intimation: Node must intimate to –HA –Correspondent node Binding Ack: Node may expect an Ack Life-time: Node should know its likely time of association.

Session: 14S. K. Nayak14.36 Binding Update Option Type AHLRESUMELIFE TIME IDENTIFICATION CARE-OF ADDRESS Node maintains a counter and increments it as and when it acquires a c/o addr Binding update is identified by this field. Care of address acquired by node is reflected in this field Binding update survives for the time specified as Life Time Distinguishing Link-Local address H=1 : Request to serve as Home Agent L=1 : Link-Local Address included A=1 : Ack reqd. HOME LINK LEVEL ADDRESS Option Length

Session: 14S. K. Nayak14.37 Binding Ack Option Type Option Length IDENTIFICATION Refrsh Life Time Field copied from received Binding-update Life -time for which Binding will be cached

Session: 14S. K. Nayak14.38 Mobile Node Operation IP decapsulation Send Binding updates Receive Binding Ack Keep track of Nodes (because of Life-time) Send Binding Updates using Routing Header

Session: 14S. K. Nayak14.39 Correspondent Node Operations Process received Binding Updates Send Binding-Ack Maintain Binding-Cache Maintain Security Association

Session: 14S. K. Nayak14.40 Packet Delivery at CN Entries in Binding- Cache Yes No Send to HA Using Normal Procedure Send Directly to Care-of Addr ICMP Error Message Recd Yes Delete entry in Binding -Cache Wait for fresh Binding

Session: 14S. K. Nayak14.41 Home Agent Operations Send Binding-Ack to Binding Updates Encapsulate Packets for tunneling Neighbour Advertisement Proxy Neighbour Advertisement Home Agent Discovery Handle returned ICMP errors

Session: 14S. K. Nayak14.42 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

Session: 14S. K. Nayak14.43 Change of foreign agent CNHAFA old FA new MN t request update ACK data MN changes location registration update ACK data warning update ACK data registration

Session: 14S. K. Nayak14.44 Mobile IP Summary Mobile node moves to new location Agent Advertisement by foreign agent Registration of mobile node with home agent Proxying by home agent for mobile node Encapsulation of packets Tunneling by home agent to mobile node via foreign agent