Transcript Switches

An Introduction
to Networking
Chapter 1
Panko’s Business Data Networks and Telecommunications,
6th edition
Copyright 2007 Prentice-Hall
May only be used by adopters of the book
The Chapter
• This chapter is a survey of
the key concepts we will see
in this course
• The rest of the book
essentially fleshes out the
concepts we will see in this
chapter
2
Part I: Basic Networks
Concepts
Concepts we will see
throughout the book
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.
Network
4
Figure 1-2: The Internet and Applications
Webserver
Application
E-Mail Client
Client
Computer
Browser
Mobile Client
Computer
The Internet
(Global Transmission System
To Carry Application Data)
The Internet is a Global
TRANSMISSION System
Applications are DELIVERED By
The Internet
Server Computer
(Webserver)
E-Mail
Application
Server Computer
(Mail Server)
5
Figure 1-1: Basic Networking Concepts
• The Internet
– Client/server applications
• PC clients receive service from servers
• Many C/S applications need special clients
• Many (but not all) C/S applications only need a
browser
Client Program
Client Computer
Server Program
Server Computer
6
Figure 1-1: Basic Networking Concepts
• Internal Corporate Networks
– For transmission among computers within a corporation
– Transaction processing applications
• High-volume clerical(書記的) applications
• Accounting, payroll, billing, etc.
– Voice over IP (VoIP)
7
Figure 1-1: Basic Networking Concepts
• Data Communications and Telecommunications
– Data communications, as the name suggests, involves
the transmission of data (text, numbers, pictures, and
other information).
– In turn, telecommunications is the transmission of voice
and video, including ordinary telephony and broadcast
and cable television.
– Beginning to converge
8
Figure 1-1: Basic Networking Concepts
• Digital Transmission
– Information is first converted into a string of ones and
zeros (binary)
– Next, the ones and zeros are converted into signals that
propagate over transmission media.
– More detail in Chapter 3
Hello…
101001
12345…
1000100
9
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
Figure 1-3: Elements of a Network
Client Application
Server Application
Message (Frame)
Client
Computer
Access
Line
Switch
2
Networks connect
Switch
applications on different computers.
Switch
1 Applications are all users care about
Trunk
3
Line
Mobile
Client
Server
Computer
Outside
World
Wireless
Access Point
Router
11
Figure 1-3: Elements of a Network
Client Application
Server Application
Message (Frame)
Client
Computer
Mobile
Client
Access
Line
Switch
2
Networks connect computers:
clients (fixed and mobile) and servers
Switch
Switch
1
Trunk
3
Line
Server
Computer
Outside
World
Wireless
Access Point
Router
12
Figure 1-3: Elements of a Network
Client Application
Server Application
Message (Frame)
Data Link
Client
Computer
Switch
Computers
(and routers)
1
usually communicate
Trunk
by sending messages
Line
called frames
Mobile
Client
Wireless
Access Point
Server
The path Computer
a frame takes
Switch
is called its data link
3
Outside
World
Router
13
Figure 1-3: Elements of a Network
Client Application
Server Application
Message (Frame)
Frame
to Sw1
Frame
to Sw2
Client
Computer
Frame
To Sw3
Switch 2
Switch 1
Switch 3
Trunk
Line
Mobile
Client Switches Forward
Frames Sequentially
Wireless
Access Point
Frame
to Server
ServerComputer
Outside
World
Switch
4
Router
14
Figure 1-5: Ethernet Switch Operation
C3- is out Port 15
Switching Table
Port
Host
10
A1-44-D5-1F-AA-4C
2
13
B2-CD-13-5B-E4-65
15
15
C3-2D-55-3B-A9-4F
C3-2D-55-3B-A9-4F
16
D4-47-55-C4-B6-F9
D4-47-55-C4-B6-F9
Switch
3
Frame to C3…
Port 15
Frame to C3…
1
A1-44-D5-1F-AA-4C
B2-CD-13-5B-E4-65
A1- sends a frame to C3-
C3-2D-55-3B-A9-4F
Switch sends frame to C315
Figure 1-3: Elements of a Network
Small Switches (Stacked):
Both sizes of switches are
48 cm (19 inches) wide
Large Switch
16
Figure 1-3: Elements of a Network
Client Application
Server Application
Message (Frame)
Switch
2
Access
Line
Client
Computer
Wireless Access
Switch
Points Connect
1
Wireless Stations Trunk
Line
to Switches
Mobile
Client
Wireless
Access Point
Server
Computer
Switch
3
Outside
World
Switch
4
Router
17
Figure 1-3: Elements of a Network
Client Application
Server Application
Message (Frame)
Client
Computer
Switch
2
Access
Line
Switch
1
Trunk
Line
Routers connect networks
to the outside world;
Switch
Treated just like computers
3
in single networks
Mobile
Client
Wireless
Access Point
Server
Computer
Outside
World
Switch
4
Router
18
Figure 1-3: Elements of a Network
Client Application
Server Application
Message (Frame)
Access
Line
Client
Computer
Switch
2
Access Lines
Connect Computers
Switch
to Switches
1
Trunk
Line
Mobile
Client
Wireless
Access Point
Server
Computer
Switch
3
Outside
World
Switch
4
Router
19
Figure 1-3: Elements of a Network
Client Application
Server Application
Message (Frame)
Client
Computer
Switch
2
Access
Line
Switch
1
Mobile
Client
Trunk Lines Connect
Switches to Switches
and
Wireless
Switches to Routers
Access Point
Trunk
Lines
Switch
4
Server
Computer
Switch
3
Trunk
Line
Outside
World
Router
20
Figure 1-4: Packet Switching and Multiplexing
Breaking Communications into
Small Messages is Called
Packet Switching, even if the
Messages are Frames
AC
Client
Computer A
AC
AC
AC
AC
BD
AC
Server
Computer C
Trunk Line
BD
Access
BD
Line
Multiplexing Mixes
BD
the Messages of
Multiple Conversations
on a Trunk Line
Mobile Client
Computer B
So Packet Switching
Reduces the Cost of Trunk Lines
Router D
21
Network Elements: Recap
• Applications (the only element that users care about)
• Computers
– Clients
– Servers
• Switches and Routers
• Transmission Lines
– Trunk lines
– Access Lines
• Messages (Frames)
• Wireless Access Points
Never talk about an
innovation “reducing cost,”
“increasing speed,” etc.
without specifying
which element is
cheaper or faster.
For example, multiplexing
only reduces the cost of
trunk lines; other
costs are not decreased
22
Part III: Transmission
Speed
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
103 • Kilobits per second (kbps)-note the lowercase k
106 • Megabits per second (Mbps)
109 • Gigabits per second (Gbps)
1012 • Terabits per second (Tbps)
24
Figure 1-6: Transmission Speed
• Measuring Transmission Speed
– What is 23,000 bps in metric notation?
– What is 3,000,000,000 bps in metric notation?
– What is 15,100,000 bps in metric notation?
• Occasionally measured in bytes per second
• Written as Bps
25
Figure 1-6: Transmission Speed
• Writing Transmission Speeds
– The rule for writing speeds (and metric numbers in
general) 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).
26
Figure 1-6: Transmission Speed
• Writing Transmission Speeds
– 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
• Multiple the metric suffix Mbps by 1,000
– Gbps
• Result:
– 1.2 Gbps
– When you make either the number or the metric smaller,
you have to make the other one bigger
27
Figure 1-6: Transmission Speed
• Writing Transmission Speeds
– 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
28
Figure 1-6: Transmission Speed
• Writing Transmission Speeds
– How should you write the following in proper form?
• 549.73 kbps
• 0.47 Gbps
• 11,200 Mbps
• .0021 Gbps
29
Figure 1-6: Transmission Speed
• Rated Speed Versus Throughput
– Rated speed is the speed a network should provide,
based on standards
– Throughput is the speed a network actually provides
– We will use this distinction constantly throughout this
book
30
Figure 1-6: Transmission Speed
• Rated Speed Versus Throughput
– When transmission capacity is shared by multiple users,
• The total shared throughput is the aggregate
throughput
• Individual throughput is what individuals receive as a
fraction of the aggregate throughput
31
Part IV: LANs and WANs
First Bank of Paradise (FBP)
• The book’s running case study
– Composite mid-size bank in Hawaii
– Banks are fairly “typical” firms, although they have
stronger need for security
– Warren Chun is the chief information officer (CIO)
– Yvonne Champion is the network manager
33
First Bank of Paradise (FBP)
• Annual Revenues: $4.5 Billion
• Operations
– 60 Branches
– 375 ATMs (Automated Teller Machines)
• Network
– 700 Ethernet switches
– 450 Routers
34
First Bank of Paradise (FBP)
• Computers
– 2,300 desktop and notebook user PCs
– 130 Windows servers
– 60 Unix servers
• Information Systems Staff
– 112 people
35
Figure 1-8: LANs Versus WANs
Characteristics
LANs
Scope
For transmission within For transmission
a site. Campus,
between sites
building, and SOHO
(Small Office or Home
Office) LANs
Cost per bit Transmitted
Low
High
Unshared 100 Mbps
to a gigabit per
second to each
desktop. Even faster
trunk line speeds.
Shared 128 kbps to
several megabits per
second trunk line
speeds
Typical Speed
WANs
36
Figure 1-8: LANs Versus WANs
Characteristics
Management
Choices
LANs
WANs
On own premises, so
firm builds and
manages its own LAN
or outsources the
Work
Must use a carrier with
rights of way for
transmission in public
Area. Carrier handles
most work but
Charges a high price.
Unlimited
Only those offered by
carrier
37
Figure 1-9: Local Area Network (LAN) in a
Large Building
Multi-floor
Office Building
The bank has multiple
LANs—one at each site
38
Figure 1-9: Local Area Network (LAN) in a
Large Building
Client
Server
Wall Jack
Workgroup Switch 2
Workgroup Switch 1
Wall Jack
To
WAN
Router
Core Switch
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
39
Figure 1-10: Workgroup Switch
(19 inches / 48 cm Wide)
48 cm (19 in.)
Workgroup Switch
with 16 ports
Wire cord going
out to a computer
or to another switch
40
Figure 1-7: The First Bank of Paradise’s Wide
Area Networks (WANs)
Frame Relay Network
Branch Office
North Shore
Operations
OC3 Private Leased Line
T3
Bank has multiple
T3
facilities connected
by multiple WANs
Headquarters
OC-n: Optical Carrier-n, n × 51.84 Mbit/s
T3: T-carrier Third Level, 44.736 Mbit/s
41
Recap: LANs and WANs
• LANs transmit data within
corporate sites
• WANs transmit data
between corporate sites
• Each LAN or WAN is a
single network
• LAN costs are low and
speeds are high
WAN
• WAN costs are high
and speeds are lower
42
Part V: Internets
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.
Application
Application
LAN
LAN
WAN
Router
Router
44
Figure 1-11: Internets
• Internet Components
– All computers in an internet are called hosts
• Servers, clients, PDAs, cellphones, etc.
PDA
(Host)
Client PC
(Host)
VoIP Phone
(Host)
Internet
Server
(Host)
Cellphone
(Host)
45
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-23-9BE8-67-47)
46
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
47
Figure 1-11: Internets
• Packets are carried within frames
– One packet is transmitted from the source host to the
destination host
• Its IP destination address is that of the destination
host
– In each network, the packet is carried in (encapsulated in)
a frame (Figure 1-12)
– 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
48
Figure 1-12: Internet with Three Networks
Host A
Packet
Network X
Network Z
A packet goes all the
way across the internet; Route A-B
It’s path is its route
R1
Network Y
R2
Host B
49
Figure 1-12: Internet with Three Networks
• Messages in single networks (LANs or WANs) are
called frames
• Message in internets are called packets
– Travel from the source host to the destination host
across the entire internet
• Within a single network, the packet is encapsulated in
(carried in) the network’s frame
Packet
Package
(Packet)
Truck
(frame)
Frame
50
Figure 1-12: Internet with Three Networks
In Network X, the Packet is Placed in Frame X
Frame X
Packet
Details in
Network X
Switch
Host A
10.0.0.23
AB-23-D1-A8-34-DD
Data link
A-R1
Switch
X1
A route is a packet’s
path through the Mobile
internetClient
Host
Route A-B
Network X
Switch
X2
Switch
Server
A data Link is a
Host
frame’s path through
its single network
Router R1
D6-EE-92-5F-C1-56
51
Figure 1-12: Internet with Three Networks
Details in
Network Y
To
Network X
Route
A-B
Router R1
Data Link
R1-R2
To
Network Z
Frame Y
Packet
Router R2
AF-3B-E7-39-12-B5
Network Y
52
Figure 1-12: Internet with Three Networks
Data Link
R2-B
Host B
www.pukanui.com
1.3.45.111
55-6B-CC-D4-A7-56
Details in
Network Z
Frame Z
Packet
Switch
Z1
Switch
Switch
Z2
Switch
Mobile Client Host
Router R2
Mobile Client
Computer
Router
Network Z
53
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?
54
Recap
• Switches versus Routers
– Switches move frames through a single network (LAN
or WAN)
– Routers move packets through internets
• Messages
– Messages in single networks are called frames
– Messages in internets are called packets
– Packets are encapsulated within (carried inside)
frames
55
Figure 1-12: Internet with Three Networks
• Spelled in lowercase, “internet” is any internet
• Spelled in uppercase, “Internet” is the global Internet
56
Figure 1-13: Converting IP Addresses into
Dotted Decimal Notation
IP Address (32 bits long)
10000000101010110001000100001101
Divided into 4 bytes. These
10000000 10101011 00010001 00001101
are segments.
Convert each byte to
decimal (result will be
between 0 and 255)*
Dotted decimal notation
(4 segments separated by
dots)
128
171
17
13
128.171.17.13
*The conversion process is described in the Hands On section
at the end of the chapter.
57
Figure 1-25: Windows Calculator
1. Open Calculator, which is in
the Program Group Accessories
2. Select View,
Scientific
58
Figure 1-25: Windows Calculator
4. Enter data on keypad
(Limit is 8 bits for Binary)
3. Enter initial
data type here
Dec = Decimal
Bin = Binary
59
Figure 1-25: Windows Calculator
6. Observe answer
5. Enter final
data type here,
observe results
Initial zeros are dropped,
so answer is 0001 0111
60
Figure 1-14: The Internet, internets,
Intranets, and Extranets
• The Global Internet
– As noted earlier,
• Spelled with a lowercase i, internet means any
internet
• Spelled with a uppercase I, Internet means the global
Internet
61
Figure 1-14: The Internet, internets,
Intranets, and Extranets
• The Internet (Figure 1-18)
– Host computers
– Internet service providers (ISPs)
• Required to access the Internet
• Carry your packets across the Internet
• Collect money to pay for the Internet
– The Internet backbone consists of many ISPs
• ISPs interconnect at Network access points (NAPs) to
exchange cross-ISP traffic
62
Figure 1-17: The Internet
Webserver
Host
Computer
User PC
Host
Computer
Access
Line
Internet Backbone
(Multiple ISP Carriers)
Access
Line
Router
NAP
ISP
NAP
ISP
NAP
ISP
ISP
User PC’s
Internet Service
Provider
NAP = Network Access Point
Webserver’s
Internet Service
Provider
63
Figure 1-18: Subnets in an Internet
LAN 2
LAN 1
Router
R1
LAN Subnet
60.4.3.x
LAN Subnet
10.1.x.x
LAN Subnet
10.2.x.x
LAN Subnet
10.3.x.x
Router R2
LAN Subnet
60.4.15.x
WAN
Subnet
123.x.x.x
Router
R4
LAN Subnet
60.4.7.x
LAN Subnet
60.4.131.x
Router R3
Note: Subnets are single networks (collections of switches, transmission lines)
64
Figure 1-19: Terminology Differences for SingleNetwork and Internet Professionals
By Single-Network
Professionals
By Internet
Professionals
Single Networks Are
Called
Networks
Subnets
Internets Are Called
Internets
Networks
In this book, to avoid confusion,
we will call internets “internets”
and subnets “single networks”
65
Figure 1-14: The Internet, internets,
Intranets, and Extranets
• Intranets
– An intranet is an internal internet for use within an
organization
– Based on the TCP/IP standards created for the Internet
“Intra” means “within”
66
Figure 1-14: The Internet, internets,
Intranets, and Extranets
• Extranets
– To connect multiple firms
• Only some computers from each firm are on the
extranet
– Use TCP/IP standards
“Extra” means “outside”
67
Figure 1-14: The Internet, internets,
Intranets, and Extranets
• Intranets, Extranets, and the Internet
– Confusingly, both intranets and extranets can use the
Internet for some of their transmission capacity
68
Figure 1-15: Routers
(19 inches / 48 cm Wide)
69
Figure 1-16: Small Router for a Branch
Office (19 inches / 48 cm Wide)
Height: 1U = 1.75 inches (Pizza Box)
70
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)
71
Figure 1-21: Dynamic Host Configuration
Protocol (DHCP)
Pool of
IP Addresses
Client PC
A3-4E-CD-59-28-7F
DHCP
Server
DHCP Request Message:
“My 48-bit Ethernet address is A3-4E-CD-59-28-7F”.
Please give me a 32-bit IP address.”
72
Figure 1-21: Dynamic Host Configuration
Protocol (DHCP)
Pool of
IP Addresses
Client PC
A3-4E-CD-59-28-7F
DHCP
Server
DHCP Response Message:
“Computer at A3-4E-CD-59-28-7F,
your 32-bit IP address is 11010000101111101010101100000010”.
(Usually other configuration parameters as well.)
73
動態主機組態協定(DHCP)
• Dynamic Host Configuration Protocol
• 自動設定電腦的
– IP位址(163.22.20.223)
– 子網路遮罩(255.255.255.0)
– 預設通訊閘(163.22.20.254)
– 領域名稱伺服器(163.22.2.1)
–…
• winipcfg (Win 98/Me)
• ipconfig /all (Win 2000/XP)
74
Ipconfig (Windows XP, 2000)
• ipconfig
• ipconfig /all
• ipconfig /release
• ipconfig /renew
75
1
2
3
控制台  網路和網際網路連線
76
77
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)
78
Figure 1-22: The Domain Name System
(DNS)
1.
Client Host
wishes to reach
Voyager.cba.hawaii.edu;
Needs to know
its IP Address
DNS Table
Host Name
IP Address
…
…
…
…
Voyager.cba.hawaii.edu 128.171.17.13
…
…
2. Sends DNS Request Message
“The host name is Voyager.cba.hawaii.edu”
Voyager.cba.hawaii.edu
128.171.17.13
Local
DNS
Host
79
Figure 1-22: The Domain Name System
(DNS)
DNS Table
Host Name
IP Address
…
…
…
…
Voyager.cba.hawaii.edu 128.171.17.13
…
…
4. DNS Response Message
“The IP address is 128.171.17.13”
5.
Client sends packets to
128.171.17.13
DNS
Host
3.
DNS Host
looks up
IP address
Voyager.cba.hawaii.edu
128.171.17.13
80
Figure 1-22: The Domain Name System
(DNS)
The local DNS host
sends back the response;
the user is unaware that
other DNS hosts were involved
Client Host
DNS Table
Host Name
IP Address
…
…
…
…
Voyager.cba.hawaii.edu 128.171.17.13
…
…
Local
DNS
Host
1. DNS Request Message
3. DNS Response Message
If local DNS host does not
have the target host’s IP address,
it contacts other DNS hosts
to get the IP address
2.
Request &
Response
Anther DNS Host
81
• nslookup
• ipconfig /displaydns
• ipconfig /flushdns
• ipconfig /registerdns
82
Part VI: Security
Figure 1-23: Firewall and Hardened Hosts
Allowed Legitimate
Packet
Border
Firewall
Attacker
The
Internet
Hardened
Server
Border firewall
should pass
legitimate packets
Legitimate
Packet
Hardened
Client PC
Legitimate
Host
Log File
Internal
Corporate
Network
84
Figure 1-23: Firewall and Hardened Hosts
Hardened
Server
Border firewall
should deny (drop)
and log
attack packets
Border
Firewall
Attack
Packet
Attacker
The
Internet
Hardened
Client PC
Denied
Attack
Packet
Log File
Legitimate
Host
Internal
Corporate
Network
85
Figure 1-23: Firewall and Hardened Hosts
Hardened
Server
Attack
Packet
Border
Firewall
Attack
Packet
Attacker
The
Internet
Hardened
Client PC
Attack
Packet
Hosts should
Denied be hardened
Attack
against attack packets
Packet that get through
Legitimate
Host
Internal
Corporate
Log File
Network
86
Figure 1-24: Cryptographic Protections
• Cryptography
阻撓
– The use of mathematical operations to thwart attacks on
message dialogues between pairs of communicating
parties (people, programs, or devices)
• Cryptography is Expensive
– Usually only sensitive dialogues are cryptographically
secured
• Initial Authentication
騙子
– Determine the other party’s identity to thwart impostors
87
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
88
Recap: Security
• Security
– Firewalls
– Hardened Hosts
– Cryptographic security
for sensitive dialogues
• Initial authentication
• Encryption for
confidentiality
• Electronic signatures for
authentication and
message integrity
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