2002 년 2 학기 이동인터넷프로토콜 1

Mobile IP:Overview

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Mobile IP overview

• Is Mobile IP an official standard?• What problems does Mobile IP solve?• What is the scope of Mobile IP solution?• What are the requirements for mobile IP?• What are the design goals for Mobile IP?• What assumptions does Mobile IP make?• Where does Mobile IP reside?• At a 10,000-foot level, how does Mobile IP work?

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Is Mobile IP a standard?

• proposed standard (Nov. 1996)• on its way to Internet standard• related RFCs:

– RFC2002, 2003,2004,2005,2006, 1701

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What problems does mobile IP solve?

• provides a solution for mobility on Internet which is scalable, robust, secure, and maintains ongoing communications as nodes change link.

• provides a mechanism for routing IP packets to mobile nodes which may be connected to any link while using their permanent IP address

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What is the scope of the mobile IP solution?

• network layer solution to node mobility in the Internet• set up routing tables in appropriate nodes, such that IP

packets can be sent to mobile nodes not connected to their home link

• specialized routing protocol for nodes which change locations

• supports heterogeneous mobility: allow movement between different media types

cf) CDPD, IEEE 802.11 supports homogeneous mobility• deals with only network layer solutions cf) Improving the TCP performance is out of the scope

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What are the requirements for mobile IP?

• A mobile node– communicates with other nodes after changing link-

layer contact

– communicates using only its home IP

– communicates with other computers with no mobile IP implementation

– not exposed to security threats over those with fixed connection (#Figure 8. 3)

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What are the design goals for mobile IP?

• make the size and frequency of routing updates for mobile IP as small as possible

• make simple for easy implementation on constrained nodes (pagers, cellular phones, PDAs)

• avoid use multiple addresses (running out of addresses)

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What assumptions does mobile IP make?

• assumes there exists an infrastructure of routers and links that is capable of routing packets to any node which is connected to its home link

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Where does mobile IP reside?

• Mobile node: a node which change its point of attachment to the Internet from one link to another while maintaining on-going communication using only its IP home address

• Home agent: a router with an interface on the mobile node’s home link– knows the mobile node’s current address (care-of address)

– advertises reachability to the network-prefix of the mobile node’s home address

– intercepts packets destined to the mobile node’s home address and tunnels them to the mobile node’s current location (care-of address)

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Where does mobile IP reside?

• Foreign agent: a router on a mobile node’s foreign link– assists the mobile node in informing its home agent of

its current care-of address

– provides a care-of address and de-tunnels packets for the mobile node

– serves as a default router for packets generated by the mobile node

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Tunneling• tunnel:

– the path followed by a first packet while it is encapsulated within the payload portion of a second packet

– #Fig. 4-2

– IP in IP

– applications: multicast backbone(Mbone), IPv4 and IPv6, Mobile IP

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Home address, Home link and Home agent

• Home address: permanent IP address• Home link: network-prefix of the home address• Home agent: a router that has at least one interface

on the mobile node’s home link• A mobile node can be “never at home” or

“always away from home”– virtual home link existing only as software within home

agent

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Care-of address, foreign link, and foreign agent

• care-of address:– an IP address associated with a mobile node that is

visiting a foreign link

– changes everytime the mobile node moves from one foreign link to another

– exit-point of a tunnel from the home agent toward the mobile node

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Care-of address, foreign link, and foreign agent

• foreign agent care-of address:– an IP address of a foreign agent which has an interface

on the foreign link being visited by a mobile node (using the IP Destination address of a registered mobile node, looks up appropriate interface forwards the packet to the mobile node)

– from foreign agent care-of address to a mobile node: use link-layer addressesuse link-layer addresses

– network-prefix of a foreign agent care-of address need not equal the network-prefix of the foreign link

– can be shared by many mobile nodes simultaneously

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Care-of address, foreign link, and foreign agent

• collocated care-of address:– an IP address temporarily assigned to an interface of

the mobile node itself (using DHCP or PPP’s IPCP)– network-prefix of a collocated care-of address should

equal the network-prefix of the foreign link being visited by a mobile node

– might be used when no foreign agents are available– the mobile node performs similar processing as the

router

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Can agents be hosts or must they be routers?

• “router” forwards packets not explicitly addressed to itself

• if we implement a home agent on a PC, and it starts tunneling packets to mobile nodes, it “becomes” a router

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Who owns the mobile nodes and the agents?• Generally, same administration owns a mobile

node, its home agent, home link• a foreign link may be on any networks• #Fig. 10-1 in Solomon

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A bird’s eye on how mobile IP works

• agent advertisements by home agents and foreign agents

• mobile nodes examine agent advertisements and determine whether connected to home or foreign link

• mobile node connected to a foreign link obtain a care-of address (an IP)

• mobile node registers its care-of address with its home agnet

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A bird’s eye on how mobile IP works

• home agent advertises reachability to mobile node’s home address (network-prefix)

• home agent intercepts packets destined to node’s home address and tunnels them to the mobile node’s care-of address

• foreign agent removes the original packet from the tunnel and delivers the original packet to the mobile node over the foreign link (link-layer addresses)

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A b

ird’s glan

ce at Mob

ile IP