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CSCI 233Internet Protocols

Class 2

Dave Roberts

More on Course Mechanics

• 50 word limit on homework answers and exam answers

• “Which is better?”--trick question! Usually there is no “better”, there are tradeoffs

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Good Citizen Principle• In a crisis, when resources are

short, we tend to hoard resources• The hoarding creates shortages• What if, in a crisis, each of us

reduced our use of scarce resources?

• The Internet operates on the Good Citizen Principle

Good Citizen PrincipleWhen a resource is scarce, instead of trying to claim as much of it as possible, reduce your use of that resource until the scarcity passes

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This is an important Internet design principle.

We will see it again and again.

Important Internet Principles

1. Good Citizen Principle—when a resource is scarce, reduce your demand for it

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Tonight• Review of networking technologies• Internetworking• Protocol Layering• Internet addresses

Early Ethernet

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• Stiff wire, hard to bend

• Vampire connectors reduce performance

• Hard to change when offices are rearranged

Modern Ethernet

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Ethernet Frame

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Header Payload

Internetworking• How to interconnect networks?

– Application level

– Network Level• Users attach to a local network• Internetworking software hides details of

networks, forwards information among them

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Internet Architecture

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The User’s View

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ThisLooks Like This

Protocol Layering• Internet protocols are organized

into levels, called “layers”• Each layer deals with certain

topics• Layers make protocols easier to

understand

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Just Think of Problems• Hardware failure• Network congestion• Packet loss• Data corruption• Data duplication• Data arriving out of sequence

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Layering and Problems• Layering allows a problem to be

solved in just one layer• Especially, applications do not

have to deal with network problems

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Layers

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Layering Models• OSI 7-layer model

– Developed for Open System Interconnect protocol family

– International standard developed over years by ISO

– Failed• TCP/IP 5-layer model

– Developed by US DARPA for military use– Widely adopted, basis for the Internet

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OSI Model• We may have an exercise or two• The course is about Internet

protocols• You will never be examined on the

OSI model

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TCP-IP 5-Layer Reference Model

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VERY

IMPORTANT!!!!

Important Boundaries

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In Reality

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How It Works

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What’s Happening1. Sender hands message to transport

layer, which packages message and hands it to Internet layer

2. Internet layer packages message as an IP datagram, with IP addresses, then hands it to network layer

3. Network interface puts message into an Ethernet frame, with Ethernet addresses, and sends through network adapter

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Encapsulation

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IP Demultiplexing

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INTERNET ADDRESSING

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The Internet• Is it a physical or virtual network?• It’s a virtual network, defined by

protocols that run on hosts and routers.

• Internet protocols make the Internet look like a world-wide uniform network, although it encompasses many networks that are very different from each other.

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Internet Addresses• Each host connection on the

Internet has a unique Internet address

• The addresses are designed to make forwarding of Internet packets simple

• An IP address has two parts: a prefix that identifies a network and a suffix that identifies a host on the network 28

Need for Control• To avoid conflicts in address use, some

sort of authority is needed• It makes sense to assign addresses in

blocks, not one at a time• ICANN (Internet Corporation for

Assigned names and Numbers) oversees IP address assignment

• Originally assigned in blocks of Class A, B and C addresses

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IPv6 Addressing• Each address is 128 bits• Enough addresses for every

person on earth to have an internet with three times the addresses of the present Internet!

• 1024 addresses per square meter of the earth’s surface

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IPv6 Address Assignments

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IPv4 to IPv6 Transition

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IPv6 Address Split

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Question• How many Internet addresses can one

host have?• As many as it has network adapters

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IP Addresses

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Functions of Internet Addresses

• Provide a unique identification for a particular interface between a device and the network so that a datagram can be delivered to the correct recipient

• Enable a path to be found across the Internet to reach the recipient, a process called routing

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IP and Ethernet Addresses

• Is the IP address the same as the Ethernet address?– No!

• What is the role of each?– Ethernet: delivery on the local area

network– IP: forwarding across the Internet

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IPv4 Address• 32-bit integer, unique for each

host on the network, used in all communication with the host

• <IP address> ::= <netid> <hostid>– Netid: identifier of a network– Hostid: identifier of a host on the

network

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Dotted Decimal Notation

32-bit Internet address

10000000 00001010 00000010 00011110

Is written

128.10.2.30

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Classes of IPv4 Addresses“Classful” addresses—types A, B and C below

first 2 bits distinguish 3 primary classes

Design of these classes is for efficient routingThere have been other refinements—to discuss later

Class Determination Algorithm

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Address Class Characteristics

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Host Capacities

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IP Address Split

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Advantages of Classful Addressing

• Simplicity and clarity—addresses and their setup are very easy to understand

• Flexibility to accommodate different sizes of networks

• Ease of separating host address for routing

• Allows for reservation of some addresses for special purposes

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Classless IPv4 Addressing

• Temporary addressing scheme that does away with class A, B, C addresses

• Network prefix can be any specified length

• Forwarding techniques expanded to account for this: called Classless Inter-Domain Routing (CIDR)

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Special IP Addresses

IP and Ethernet Addresses

• Physical transmissions are all made using Ethernet addresses across a local area network

• IP addresses give destinations across the Internet

• When a router gets an IP datagram, it decides whether to send it on to another router or deliver it locally

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Address Resolution• If the router decides to deliver

locally, then it must find out the local network’s Ethernet address that corresponds to the IP address in the datagram

• We’ll talk about address resolution next week!!

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