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Mobile IP

Why do we need it?

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Acknowledgement

• Some figures and texts are from:– Solomon

– Perkins

– Govindan

– Kurose

– Peterson & Davie

– Huitema

– Heijenk

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Motivation

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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

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Mobility is not wirelessness

• Mobility is a topological capability

• connectivity is maintained regardless of the location or motion of the mobile entity

cf) IEEE 802.11 (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

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Mobile IP vs CDPD or wireless LAN

•

Mobile IP CDPD Wireless LANarea wide wide localmedium any cellular any LAN mediumspeed depends on medium~11kbps 1-2 Mbpslayer network link-layer link-layerunique IP yes yes no

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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

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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

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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

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Route advertisement in ICMP

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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

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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 description0 0 echo reply (ping)3 0 dest. network unreachable3 1 dest host unreachable3 2 dest protocol unreachable3 3 dest port unreachable3 6 dest network unknown3 7 dest host unknown4 0 source quench (congestion control - not used)8 0 echo request (ping)9 0 route advertisement10 0 router discovery11 0 TTL expired12 0 bad IP header

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The need for mobility

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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?

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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

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Example

• (#Fig. 3-1 in Solomon)– Host4 moves from 2.0.0 network to 4.0.0 network– Host1 generates an IP packet for Host4(2.0.0.4)– The IP packet is sent to RouterA (default for Host1)– Router A finds an entry for 2.0.0 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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Can’t you solve this problem with host-specific routes?

• use the longest-matching routing rule– place host-specific routes in the routing tablesex) Router A: 2.0.0.4/32 next hop = 3.0.0.252, interface = “c”Router B: 2.0.0.4/32 next hop = 3.0.0.252, interface = “c”Router C: 2.0.0.4/32 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

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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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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

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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

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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

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Can’t you just solve this at the link layer?

• IEEE 802.11 (wireless LAN):– geographically constrained

– transceiver bridges wireless medium and wired networks

– change of location requires change of IP address

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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