Chapter1 modified

An Introductionto Networking

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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

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

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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

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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

Figure 1-8: LANs Versus WANs

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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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

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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

LANLAN WANWAN LANLAN

Router Router

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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 1-23: 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

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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

Technology

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