2002 년 2 학기고급 인터넷 1 Mobile IP Why do we need it?

2002 년 2 학기고급 인터넷 2 Acknowledgement Some figures and texts are from: –Solomon –Perkins –Govindan –Kurose –Peterson & Davie –Huitema –Heijenk

2002 년 2 학기고급 인터넷 3 Motivation

2002 년 2 학기고급 인터넷 4 What is mobility? ability to send and receive communications anytime, anywhere both source and destination devices, applications and people are free of the constraints imposed by physical location

2002 년 2 학기고급 인터넷 5 Mobility is not wirelessness Mobility is a topological capability connectivity is maintained regardless of the location or motion of the mobile entity cf) IEEE (wireless LAN): geographically constrained location independence over an area that is physically too large for any single medium such as Ethernet or RF channel cf) CDPD supports only one medium without changing IP address

2002 년 2 학기고급 인터넷 6 Mobile IP vs CDPD or wireless LAN

2002 년 2 학기고급 인터넷 7 Routing in the Internet Packets flow from link (subnetwork) to link via routers Packets are routed individually, based on their IP addresses (not on DNS name) Routing is based on the (sub)network prefix of the IP address »A mobile host must be assigned a new address when it moves

2002 년 2 학기고급 인터넷 8 Connections between Internet computers TCP connections are defined by source and destination IP addresses and port numbers Change of host address would cause the connection to break »Host address must be preserved regardless of a hosts location

2002 년 2 학기고급 인터넷 9 The Mobile IP problem A mobile host must be assigned a new address when it moves «» Host address must be preserved regardless of a hosts location

2002 년 2 학기고급 인터넷 10 Route advertisement in ICMP

2002 년 2 학기고급 인터넷 11 Internet Control Message Protocol (ICMP) Echo (ping) Redirect (from router to source host) Destination unreachable (protocol, port, or host) TTL exceeded (so datagrams don’t cycle forever) Checksum failed Reassembly failed Cannot fragment

2002 년 2 학기고급 인터넷 12 Route advertisement in ICMP Type 9 code 0: Router adv Type 9 code 16: –Mobile agents –Ignored when mobile IP is not installed Type Code description 0 0 echo reply (ping) 3 0 dest. network unreachable 3 1 dest host unreachable 3 2 dest protocol unreachable 3 3 dest port unreachable 3 6 dest network unknown 3 7 dest host unknown 4 0 source quench (congestion control - not used) 8 0 echo request (ping) 9 0 route advertisement 10 0 router discovery 11 0 TTL expired 12 0 bad IP header

2002 년 2 학기고급 인터넷 13 The need for mobility

2002 년 2 학기고급 인터넷 14 The need for mobile-IP What happens when a node changes link? Can’t you solve this problem with host-specific routes? Why not just change the node’s IP address? Can’t you just solve this at the link layer? What if I only need nomadicity?

2002 년 2 학기고급 인터넷 15 What happens when a node changes link? network-prefix routing: all nodes with interfaces on a given link have identical network-prefix portions of their IP addresses IP packets destined to a specific address will be routed toward the router which advertise reachability to the network-prefix of that address

2002 년 2 학기고급 인터넷 16 Example (#Fig. 3-1 in Solomon) –Host4 moves from network to network –Host1 generates an IP packet for Host4( ) –The IP packet is sent to RouterA (default for Host1) –Router A finds an entry for network, sends the packet to router B –Router B transmits the packet via interface b, only to find the packet is undeliverable –Router B sends an ICMP host unreachable error to Host1

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2002 년 2 학기고급 인터넷 18 Can’t you solve this problem with host-specific routes? use the longest-matching routing rule –place host-specific routes in the routing tables ex) Router A: /32 next hop = , interface = “c” Router B: /32 next hop = , interface = “c” Router C: /32 next hop = “direct”, interface = “b” home link vs. foreign link –home link: the link which has been assigned the same network-prefix as the node’s IP address –foreign link: any link other than the home link

2002 년 2 학기고급 인터넷 19 Can’t you solve this problem with host-specific routes? host-specific route is not a good solution: –number of mobile nodes increase --> increase the size of routing table –all nodes along the path from a node’s home link to its current home link must be provided with host-specific routes --> increase dramatically, as the distance grows (#Fig. 3-2 in Solomon) –mobile nodes frequently change links --> a lot of deletion and addition in the routing tables –if only minimal update is made, it is not robust –bad guy can lie about good guy’s location so that good guy can not receive anything

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2002 년 2 학기고급 인터넷 21 Why not just change the node’s IP address? Connection for communication on Internet is determined by: –source IP address, source port #, dest. IP address, dest. port # Changing IP disables an existing connection and starts a new one --> no mobility Nomadicity can be supported: –Nomadic node can terminate and restart everytime the node moves out with new IP –DHCP, PPP’s IPCP

2002 년 2 학기고급 인터넷 22 Why not just change the node’s IP address? It’s hard to locate nomadic nodes: – a node wishing to send something to a nomadic does not know it’s “current” IP –If DNS entry is updated to include the change of IP addresses for nomadic nodes, there will be a lot of traffic for DNS

2002 년 2 학기고급 인터넷 23 Can’t you just solve this at the link layer? CDPD(Cellular Digital Packet Data): –differs from cellular modem: charged not for the duration but for the amount of data actually transmitted (many CDPD modem shares a channel) –unique IP throughout the CDPD network –works with CDPD system only: link-layer solution –~11kbps

2002 년 2 학기고급 인터넷 24 Can’t you just solve this at the link layer? IEEE (wireless LAN): –geographically constrained –transceiver bridges wireless medium and wired networks –change of location requires change of IP address

2002 년 2 학기고급 인터넷 25 Can’t you just solve this at the link layer? Problems with link-layer solutions: –need new IP for new medium –N solutions for N media: A single solution over all media types is Mobile IP! –geographically constrained