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Mobile Routing in the Internet: Mobile IP
Dave Johnson
Departments of CS and ECE Rice University dbj@cs.rice.edu

David B. Johnson

The Monarch Project

Mobile Networking Architectures

Page 1

“Flat” Network Addressing
A host can move anywhere and keep the same address

But internetwork routing this way is very hard!

R1

?
R2

[2] 1

?
R3 2

David B. Johnson

The Monarch Project

Mobile Networking Architectures

Page 2

Hierarchical Network Addressing
Routers only need to know the way to each network

But if a host moves, its packets will still go to its home !

R1
Network A

[C.2] R2
Network B

B.1

R3

C.2
Network C

David B. Johnson

The Monarch Project

Mobile Networking Architectures

Page 3

IP Addressing
Originally, 3 classes of addresses:
Class A: Class B: Class C: Network Network Network Host Host Host

Can assign network number class based on expected number of hosts About two additional levels of hierarchy added to IP later through:

Subnetting : Treat some host bits as (sub)network once delivered to network Supernetting (CIDR ): Route in backbone at each hop based on variable-length common prefix David B. Johnson The Monarch Project Mobile Networking Architectures Page 4

Other Internetwork Addresses
Hierarchical address assignment is not unique to IP :
CLNP: Up to 20-byte, variable length, hierarchical address Novell IPX/SPX: 32-bit network number, 48-bit host number AppleTalk: 16-bit network number, 8-bit host number Banyan VINES: 32-bit network number, 16-bit host number DECnet Phase IV: 6-bit network number, 10-bit host number IPv6: 128-bit address with many levels of hierarchy

David B. Johnson

The Monarch Project

Mobile Networking Architectures

Page 5

Why Not Change Addresses?

Must notify all hosts with open connections:
Used to identify endpoints of connection Used within some transport protocols

Must also notify hosts using connectionless protocols Cannot change hosts with “well known” addresses Name server must be updated : Caching of addresses is used for scalability Too expensive to update quickly Just moves the problem into DNS, doesn’t solve it

David B. Johnson

The Monarch Project

Mobile Networking Architectures

Page 6

Why Solve Mobility at the IP Layer?
Mobility below the IP layer:
Many link-layer solutions exist, such as 802.11 and CDPD But these solutions are specific to a particular link type: – Can only move within a single link, not between links – Can’t move between different types of links, e.g., Ethernet to CDPD – Not all links support link layer mobility – Requires special software for each type of link

Only support at IP layer can glue together different links and types of links, like IP itself does Mobility above the IP layer: Many applications and higher layers (e.g., TCP, UDP) in use today Who knows what new higher layer protocols or applications will be created tomorrow?

Only support at IP layer can handle any higher layer

David B. Johnson

The Monarch Project

Mobile Networking Architectures

Page 7

The Basic Problems
We want to keep node IP addresses unchanged when it moves:
Movement can be transparent No need to change or restart existing connections

We want to be compatible with existing systems:
Inconvenient to change some systems, impossible to change others

We want to be scalable to many nodes in a very large network : The Internet will continue to grow rapidly The number of mobile nodes will soon grow very rapidly

We must not introduce new security holes:
Don’t allow remote redirection, denial of service, etc.

David B. Johnson

The Monarch Project

Mobile Networking Architectures

Page 8

Internet Standards
The Internet Engineering Task Force (IETF) is the principal standards development body for the Internet A large, loosely self-organized, international community of network operators and service providers,...
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