An Introduction to Networking Chapter 1. Part I: Basic Networks Concepts Concepts we will see throughout the book

An Introductionto Networking

Chapter 1

Part I: Basic Networks Concepts

Concepts we will seethroughout the book

3

Figure 1-1: Basic Networking Concepts

• What Is a Network?

– A network is a transmission system that connects two or more applications running on different computers.

NetworkNetwork

4

Figure 1-1: Basic Networking Concepts

• Client/Server Applications

– Most Internet applications are client/server applications

– Clients receive service from servers

– The client is often a browser

Client ComputerServer Computer

ServerProgram

ClientProgram

Services

Part II: The Nine Elements of a Network

Although the idea of “network”is simple, you must understand the

nine elements found in most networks

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Figure 1-3: Elements of a Network

WirelessAccess Point

MobileClient

Router

OutsideWorld

ServerComputer

ClientComputer

Switch1

Switch2

Switch3

Message (Frame)Message (Frame)

AccessLine

TrunkLine

Server ApplicationClient Application

1.Networks connect

applications on different computers.

1.Networks connect

applications on different computers.

Networks connect computers: 2. Clients (fixed and mobile) and

3. Servers

Networks connect computers: 2. Clients (fixed and mobile) and

3. Servers

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MobileClient

Router

OutsideWorld

ServerComputer

ClientComputer

Switch1

Switch3

Message (Frame)

TrunkLine


4.Computers (and routers)

usually communicateby sending messages

called frames

4.Computers (and routers)

usually communicateby sending messages

called frames

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MobileClient

Router

OutsideWorld

ServerComputer

ClientComputer

Switch4


TrunkLine


Switch 2Switch 2

Switch 1Switch 1Switch 3Switch 3

ClientSendsFrameto Sw1

ClientSendsFrameto Sw1

Sw1 SendsFrameto Sw2

Sw1 SendsFrameto Sw2

Sw2 SendsFrameTo Sw3

Sw2 SendsFrameTo Sw3

Sw3 SendsFrame toServer

Sw3 SendsFrame toServer

5.Switches Forward

Frames Sequentially

5.Switches Forward

Frames Sequentially

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Figure 1-5: Ethernet Switch Operation

A1-44-D5-1F-AA-4C B2-CD-13-5B-E4-65

Switch

D4-47-55-C4-B6-F9

C3-2D-55-3B-A9-4F

Port 15

Frame to C3…Frame to C3…

A1- sends a frame to C3-A1- sends a frame to C3-

Frame to C3…Frame to C3…

Switch sends frame to C3-Switch sends frame to C3-

Switching TablePort Host10 A1-44-D5-1F-AA-4C13 B2-CD-13-5B-E4-6515 C3-2D-55-3B-A9-4F16 D4-47-55-C4-B6-F9

Switching TablePort Host10 A1-44-D5-1F-AA-4C13 B2-CD-13-5B-E4-6515 C3-2D-55-3B-A9-4F16 D4-47-55-C4-B6-F915 C3-2D-55-3B-A9-4F15 C3-2D-55-3B-A9-4F

C3- is out Port 15C3- is out Port 15

1

2

3

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MobileClient

Router

OutsideWorld

ServerComputer

ClientComputer

Switch1

Switch2

Switch3

Switch4


AccessLine

TrunkLine


6.Wireless AccessPoints Connect

Wireless Stationsto Switches

6.Wireless AccessPoints Connect

Wireless Stationsto Switches

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MobileClient

Router

OutsideWorld

ServerComputer

ClientComputer

Switch1

Switch2

Switch3

Switch4


AccessLine

TrunkLine


7.Routers connect networks

to the outside world;Treated just like computers

in single networks

7.Routers connect networks

to the outside world;Treated just like computers

in single networks

Yes, single networks cancontain routers

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MobileClient

Router

OutsideWorld

ServerComputer

ClientComputer

Switch1

Switch2

Switch3

Switch4


AccessLine

TrunkLine

Server ApplicationClient Application8. Access Lines

Connect Computersto Switches

8. Access LinesConnect Computers

to Switches

9. Trunk Lines ConnectSwitches to Switches and

Switches to Routers

9. Trunk Lines ConnectSwitches to Switches and

Switches to Routers

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Figure 1-4: Packet Switching and Multiplexing

ClientComputer A

Mobile ClientComputer B

Router D

ServerComputer C

AC

ACAC

AC

ACAC

BD

BD

BD

BD

AccessLine

Trunk Line

Multiplexed PacketsShare Trunk Lines

So Packet SwitchingReduces the Cost of Trunk Lines

Breaking Communications intoSmall Messages is Called

Packet Switching, even if theMessages are Frames

Part III: Transmission Speed

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Figure 1-6: Transmission Speed

• Measuring Transmission Speed

– Measured in bits per second (bps)

– In metric notation:

• Increasing factors of 1,000 …

– Not factors of 1,024

• Kilobits per second (kbps)-note the lowercase k

• Megabits per second (Mbps)

• Gigabits per second (Gbps)

• Terabits per second (Tbps)

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• Measuring Transmission Speed

– What is 23,000 bps in metric notation?

– What is 3,000,000,000 in metric notation?

– What is 15,100,000 bps in metric notation?

• Occasionally measured in bytes per second• If so, written as Bps

• Usually seen in file download speeds

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• Writing Transmission Speeds in Proper Form

– The rule for writing speeds (and metric numbers in general) in proper form is that there should be 1 to 3 places before the decimal point

– 23.72 Mbps is correct (2 places before the decimal point).

– 2,300 Mbps has four places before the decimal point, so it should be rewritten as 2.3 Gbps (1 place).

– 0.5 Mbps has zero places to the left of the decimal point. It should be written as 500 kbps (3 places).

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– How to convert 1,200 Mbps to proper form

• Divide the number 1,200 by 1000

– Move decimal point three places to the left: 1.200

• Multiply the metric suffix Mbps by 1,000

– Gbps

• Result:

– 1.2 Gbps

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– How to convert 0.036 Mbps to proper form

• Multiply the number 0.036 by 1000

– Move decimal point three places to the right: 36

• Divide the metric suffix Mbps by 1,000

– kbps

• Result:

– 36 kbps

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– How should you write the following in proper form?

• 549.73 kbps

• 0.47 Gbps

• 11,200 Mbps

• .0021 Gbps

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• Rated Speed

– The speed in bits per second that you should get (advertised or specified in the standard).

• Throughput– The speed you actually get

– Almost always lower than the rated speed

• On Shared Transmission Lines– Aggregate throughput—total throughput for all users

– Individual throughput—what individual users get

Part IV: LANs and WANs

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Figure 1-8: LANs Versus WANs

CharacteristicsCharacteristics

ScopeScopeLANsLANs WANsWANs

For transmission withina site. Campus, building, and SOHO(Small Office or HomeOffice) LANs

For transmission withina site. Campus, building, and SOHO(Small Office or HomeOffice) LANs

For transmissionbetween sites

For transmissionbetween sites

BuildingLAN

BuildingLAN

HomeLAN

HomeLAN

CampusLAN

CampusLANWide Area

Network

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WANsCharacteristics LANs

Cost per bit Transmitted Low High


Typical Speed

Unshared 100 Mbps to a gigabit per second to eachdesktop. Even fastertrunk line speeds.

Shared 128 kbps to several megabits per second trunk line speeds

It’s simple economics. If the cost per unit is higher, the number of units demanded will be lower.

Corporations cannot afford high-speed for most of their WAN transmission

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Characteristics

ManagementManagement

LANs WANsWANs

On own premises, sofirm builds andmanages its own LANor outsources theWork

On own premises, sofirm builds andmanages its own LANor outsources theWork

Must use a carrier withrights of way for transmission in publicArea. Carrier handles most work butCharges a high price.

Must use a carrier withrights of way for transmission in publicArea. Carrier handles most work butCharges a high price.

ChoicesChoices UnlimitedUnlimited Only those offered bycarrier

Only those offered bycarrier

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Figure 1-9: Local Area Network (LAN) in a Large Building

Router Core Switch

Workgroup Switch 2

Workgroup Switch 1

Wall Jack

ToWAN

Wall Jack

Server

Client

Frames from the client to the server go through Workgroup Switch 2, through the Core Switch, through Workgroup Switch 1, and then to the server

Part V: Internets

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Figure 1-11: Internets

• Single LANs Versus Internets

– In single networks (LANs and WANs), all devices connect to one another by switches—our focus so far.

– In contrast, an internet is a group of networks connected by routers so that any application on any host on any single network can communicate with any application on any other host on any other network in the internet.

LANLAN WANWAN LANLAN

Application Application

Router Router

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• Internet Components– All computers in an internet are called hosts

– Clients as well as servers

Cat(IgnoresInternet)

InternetInternet

Client PC(Host)

Cellphone(Host)

VoIP Phone(Host)

PDA(Host)

Server(Host)

Host

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• Hosts Have Two Addresses

• IP Address– This is the host’s official address on its internet– 32 bits long

– Expressed for people in dotted decimal notation (e.g., 128.171.17.13)

• Single-Network Addresses– This is the host’s address on its single network– Ethernet addresses, for instance, are 48 bits long

– Expressed in hexadecimal notation (e.g., AF-23-9B-E8-67-47)

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• Networks are connected by devices called routers

– Switches provide connections within networks, while routers provide connections between networks in an internet.

• Frames and Packets

– In single networks, message are called frames

– In internets, messages are called packets

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• Packets are carried within frames

– One packet is transmitted from the source host to the destination host across the internet

• Its IP destination address is that of the destination host

Frame

PacketPacket


Router Router

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• Packets are carried within frames

– In each network, the packet is carried in (encapsulated in) a frame

– If there are N networks between the source and destination hosts, there will be one packet and N networks between the source and destination hosts, there will be one packet and N frames for a transmission

Frame

PacketPacket


Router Router

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Figure 1-12: Internet with Three Networks

Host B

Host A

Network XNetwork Y

Network Z

R1

R2

Route A-B

PacketPacket

A packet goes all theway across the internet;

It’s path is its route

A packet goes all theway across the internet;

It’s path is its route

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Mobile ClientHost

ServerHost

Switch

SwitchX2

SwitchX1

Switch

Router R1D6-EE-92-5F-C1-56

Network XRoute A-BRoute A-B

A route is a packet’spath through the internet

A route is a packet’spath through the internet

Details inNetwork X

Details inNetwork X

Data linkA-R1

Data linkA-R1

A data Link is aframe’s path through

its single network

A data Link is aframe’s path through

its single network

In Network X, the Packet is Placed in Frame X

PacketFrame X

Host A10.0.0.23

AB-23-D1-A8-34-DD

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Router R1

Router R2AF-3B-E7-39-12-B5

PacketFrame Y

ToNetwork X

ToNetwork Z

Network Y

Data LinkR1-R2

RouteA-B

Details inNetwork Y

Details inNetwork Y

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Host Bwww.pukanui.com

1.3.45.11155-6B-CC-D4-A7-56

Mobile Client Host

SwitchZ1

Switch

SwitchZ2

Switch

PacketFrame Z

Network Z

Router R2

Router

Data LinkR2-B

Details inNetwork Z

Details inNetwork Z

Mobile ClientComputer

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• In this internet with three networks, in a transmission,

– There is one packet

– There are three frames (one in each network)

• If a packet in an internet must pass through 10 networks,

– How many packets will be sent?

– How many frames must carry the packet?

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10000000101010110001000100001101 10000000101010110001000100001101

Figure 1-13: Converting IP Addresses into Dotted Decimal Notation

Divided into 4 bytes. Theseare segments.

10000000 10101011 00010001 0000110100001101

Dotted decimal notation(4 segments separated bydots)

Dotted decimal notation(4 segments separated bydots)

IP Address (32 bits long)

Convert each byte todecimal (result will bebetween 0 and 255)*

128 171 17 1313

*The conversion process is described in the Hands On section at the end of the chapter.

128.171.17.13128.171.17.13

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Figure 1-17: The Internet

2.User PC’s

Internet ServiceProvider

2.Webserver’s

Internet ServiceProvider

ISP ISP

1.User PC

HostComputer

1.Webserver

HostComputer

4.NAPs = Network Access Points

Connect ISPs

Router

NAPNAPNAPNAP

NAPNAPISP

ISP

3.Internet Backbone

(Multiple ISP Carriers)AccessLine

AccessLine

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Figure 1-18: Subnets in an Internet

LAN 1LAN 2

LAN Subnet10.1.x.x

WANSubnet

123.x.x.x

LAN Subnet60.4.3.x

LAN Subnet10.2.x.x

LAN Subnet10.3.x.x

LAN Subnet60.4.15.x

LAN Subnet60.4.7.x

Note: Subnets are single networks (collections of switches, transmission lines)Often drawn as simple lines to focus on routers for internetworking

RouterR1

Router R3

RouterR4

Router R2

LAN Subnet60.4.131.x

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Figure 1-19: Terminology Differences for Single-Network and Internet Professionals

By Single-NetworkProfessionals

By InternetProfessionals

By InternetProfessionals

Single Networks AreCalled

Networks SubnetsSubnets

Internets Are CalledInternets Are Called InternetsInternets NetworksNetworks

In this book, we will usually call internets “internets”

and subnets “single networks”

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Figure 1-14: The Internet, internets, Intranets, and Extranets

• Lower-case internet

– Any internet

• Upper-case Internet

– The global Internet

• Intranet

– An internet restricted to users within a single company

• Extranet

– A group of resources that can be accessed by authorized people in a group of companies

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Figure 1-20: IP Address Management

• Every Host Must Have a Unique IP address

– Server hosts are given static IP addresses (unchanging)

– Clients get dynamic (temporary) IP addresses that may be different each time they use an internet

• Dynamic Host Configuration Protocol (DHCP) (Figure 1-21)

– Clients get these dynamic IP addresses from Dynamic Host Configuration Protocol (DHCP) servers (Figure 1-21)

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Figure 1-21: Dynamic Host Configuration Protocol (DHCP)

Client PCA3-4E-CD-59-28-7F

DHCPServer

1. DHCP Request Message:“My 48-bit Ethernet address is A3-4E-CD-59-28-7F”.

Please give me a 32-bit IP address.”

2. Pool ofIP Addresses

3. DHCP Response Message:“Computer at A3-4E-CD-59-28-7F,

your 32-bit IP address is 11010000101111101010101100000010”.(Usually other configuration parameters as well.)

46

Figure 1-20: IP Address Management

• Domain Name System (DNS) (Figure 1-22)

– IP addresses are official addresses on the Internet and other internets

– Hosts can also have host names (e.g., cnn.com)

• Not official—like nicknames

– If you only know the host name of a host that you want to reach, your computer must learn its IP address

• DNS servers tell our computer the IP address of a target host whose name you know. (Figure 1-22)

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Figure 1-22: The Domain Name System (DNS)

Host Name IP Address … …… …Voyager.cba.hawaii.edu128.171.17.13… …


DNS Table1.Client Host

wishes to reachVoyager.cba.hawaii.edu;

Needs to knowits IP Address

2. Sends DNS Request Message“The host name is Voyager.cba.hawaii.edu”

Voyager.cba.hawaii.edu128.171.17.13

LocalDNSHost

48




DNS Table

4. DNS Response Message“The IP address is 128.171.17.13”

Voyager.cba.hawaii.edu128.171.17.13

5.Client sends packets to

128.171.17.13

3.DNS Host

looks up thetarget host’sIP address

DNSHost

49




DNS Table

Client Host

1. DNS Request Message

Anther DNS Host

LocalDNSHost

3. DNS Response Message

The local DNS hostsends back the response;the user is unaware that

other DNS hosts were involved

The local DNS hostsends back the response;the user is unaware that

other DNS hosts were involved

If local DNS host does nothave the target host’s IP address,

it contacts other DNS hoststo get the IP address

If local DNS host does nothave the target host’s IP address,

it contacts other DNS hoststo get the IP address

2.Request &Response

Part VI: Security

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Figure 1-23: Firewall and Hardened Hosts

LegitimateHost

LegitimatePacket

BorderFirewall

HardenedServer

Allowed LegitimatePacket

HardenedClient PC

InternalCorporateNetwork

Border firewallshould pass

legitimate packets

Border firewallshould pass

legitimate packets

TheInternet

Attacker

Log File

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LegitimateHost

AttackPacket

DeniedAttackPacket

HardenedServer

HardenedClient PC


Border firewallshould deny (drop)

and logattack packets

Border firewallshould deny (drop)

and logattack packets

TheInternet

BorderFirewall

Attacker

Log File

53


LegitimateHost

Attacker

AttackPacket

DeniedAttackPacket


TheInternet

BorderFirewall

HardenedServer

HardenedServer

HardenedClient PC

HardenedClient PC

AttackPacket

AttackPacket

Log File

Hosts shouldbe hardened

against attack packetsthat get through

Hosts shouldbe hardened

against attack packetsthat get through

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Figure 1-24: Cryptographic Protections

• Cryptography

– The use of mathematical operations to thwart attacks on message dialogues between pairs of communicating parties (people, programs, or devices)

• Initial Authentication

– Determine the other party’s identity to thwart impostors

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Figure 1-24: Cryptographic Protections

• Message-by-Message Protections

– Encryption to provide confidentiality so that an eavesdropper cannot reach intercepted messages

– Electronic signatures provide message-by-message authentication to prevent the insertion of messages by an impostor after initial authentication

– Electronic signatures usually also provide message integrity; this tells the receiver whether anyone has changed the message en route

Documents

An Introduction to Networking Chapter 1. Part I: Basic Networks Concepts Concepts we will see throughout the book