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![Page 1: An Introduction to Networking Chapter 1. Part I: Basic Networks Concepts Concepts we will see throughout the book.](https://reader035.fdocuments.us/reader035/viewer/2022062517/56649ea45503460f94ba91b5/html5/thumbnails/1.jpg)
An Introductionto Networking
Chapter 1
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Part I: Basic Networks Concepts
Concepts we will seethroughout the book
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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
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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
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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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Figure 1-3: Elements of a Network
WirelessAccess Point
MobileClient
Router
OutsideWorld
ServerComputer
ClientComputer
Switch1
Switch3
Message (Frame)
TrunkLine
Server ApplicationClient Application
4.Computers (and routers)
usually communicateby sending messages
called frames
4.Computers (and routers)
usually communicateby sending messages
called frames
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Figure 1-3: Elements of a Network
WirelessAccess Point
MobileClient
Router
OutsideWorld
ServerComputer
ClientComputer
Switch4
Message (Frame)Message (Frame)
TrunkLine
Server ApplicationClient Application
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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Figure 1-3: Elements of a Network
WirelessAccess Point
MobileClient
Router
OutsideWorld
ServerComputer
ClientComputer
Switch1
Switch2
Switch3
Switch4
Message (Frame)Message (Frame)
AccessLine
TrunkLine
Server ApplicationClient Application
6.Wireless AccessPoints Connect
Wireless Stationsto Switches
6.Wireless AccessPoints Connect
Wireless Stationsto Switches
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Figure 1-3: Elements of a Network
WirelessAccess Point
MobileClient
Router
OutsideWorld
ServerComputer
ClientComputer
Switch1
Switch2
Switch3
Switch4
Message (Frame)Message (Frame)
AccessLine
TrunkLine
Server ApplicationClient Application
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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Figure 1-3: Elements of a Network
WirelessAccess Point
MobileClient
Router
OutsideWorld
ServerComputer
ClientComputer
Switch1
Switch2
Switch3
Switch4
Message (Frame)Message (Frame)
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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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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Figure 1-6: Transmission Speed
• 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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Figure 1-6: Transmission Speed
• 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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Figure 1-6: Transmission Speed
• Writing Transmission Speeds in Proper Form
– 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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Figure 1-6: Transmission Speed
• Writing Transmission Speeds in Proper Form
– 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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Figure 1-6: Transmission Speed
• Writing Transmission Speeds in Proper Form
– How should you write the following in proper form?
• 549.73 kbps
• 0.47 Gbps
• 11,200 Mbps
• .0021 Gbps
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Figure 1-6: Transmission Speed
• 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
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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
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 1-8: LANs Versus WANs
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
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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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Figure 1-11: Internets
• 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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Figure 1-11: Internets
• 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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Figure 1-11: Internets
• 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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Figure 1-11: Internets
• 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 1-11: Internets
• 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
LANLAN WANWAN LANLAN
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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Figure 1-12: Internet with Three Networks
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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Figure 1-12: Internet with Three Networks
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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Figure 1-12: Internet with Three Networks
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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Figure 1-12: Internet with Three Networks
• 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.)
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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… …
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
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Figure 1-22: The Domain Name System (DNS)
Host Name IP Address … …… …Voyager.cba.hawaii.edu128.171.17.13… …
Host Name IP Address … …… …Voyager.cba.hawaii.edu128.171.17.13… …
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
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Figure 1-22: The Domain Name System (DNS)
Host Name IP Address … …… …Voyager.cba.hawaii.edu128.171.17.13… …
Host Name IP Address … …… …Voyager.cba.hawaii.edu128.171.17.13… …
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
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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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Figure 1-23: Firewall and Hardened Hosts
LegitimateHost
AttackPacket
DeniedAttackPacket
HardenedServer
HardenedClient PC
InternalCorporateNetwork
Border firewallshould deny (drop)
and logattack packets
Border firewallshould deny (drop)
and logattack packets
TheInternet
BorderFirewall
Attacker
Log File
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Figure 1-23: Firewall and Hardened Hosts
LegitimateHost
Attacker
AttackPacket
DeniedAttackPacket
InternalCorporateNetwork
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