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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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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
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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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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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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 1-14: 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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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