1.0 Aims and Objectives 1 1.1 Introduction to Data Communication 1 1.2 Classification of Computer Networks 2 1.3 Topology 4 1.4 Protocol 4 1.5 Internetworking Technologies 4 1.6 Let Us Sum Up 5 1.7 Lesson-end Activity 6

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Content







Page No.


Unit I

Lesson 1.
Introduction to Digital Communication

1.0

Aims and Objectives







1

1.1

Introduction to Data Communication





1

1.2 Classification of Computer Networks





2




1.3 Topology









4

1.4 Protocol









4


1.5 Internetworking Technologies






4

1.6 Let Us Sum Up








5

1.7 Lesson
-
end Activity







6

1.8 Points for Discussion







6

1.9 Check your Progress







6

1.10 Reference








7


Lesson 2
.
WAN Technology

2.0
Aims and Objectives







8

2.1 Introduction








8

2.2 WAN Networking Devices






8

2
.3 WAN Protocols








10

2.4 Let us Sum Up








11

2.5 Lesson end Activities







12

2.6 Points for Discussion







12

2.7 Reference









12


Lesson
3
.
History about TCP/IP

3.0 Aims and Objectives







13

3.1 Introduction








13

3.2 Internet Society








14

3.3 Request For Comments (RFC)






14

3.4
Let Us Sum Up








15

3.5
Lesson End Activities







15

3.6
Points for Discussion







15

3.7
Check your progress







16

3.8
Reference









16


Lesson 4. TCP/IP layer Architecture

4.0 Aims and Objectives







17

4.1 Introduction








17

4.2 Internet Architecture







17

4.3 TCP/IP layer Architecture






18

4.4
Let us Sum Up








22

4.5 Lesson end Activities







23

4.
6

Points for Discussion







23


4.
7

Check your progress







23

4.8 Reference









23



Lesson 5. Network Interface

5.0 Aims and Objectives







24

5.1 Introduction








24

5.2 Network Interface Card







24

5.3 Cable
T
ype and Specification Type





26

5.4 Other Protocols








27

5.5
Let us Sum Up








28

5.6
Lesson end Activities







28

5.7
Points for Discussion







28

5.8
Check you Progress







28

5.9
Reference









29


Unit II

Lesson
6.
IP Addressing Scheme

6.0 Aims and Objectives







30

6
.1 Introduction








30

6
.2 Classful Address








31

6
.3 Special Address








33

6
.4 Classless Inter
-
Domain Routing (CIDR)





34

6
.5 Multihoming








35

6.6
Let us Sum Up








35

6.7
Lesson end Activities







36

6.8
Points for Discussion







36

6.9
Check your progress







36

6.10
Reference








36


Lesson 7.
ARP & RARP

7.0 Aims and Objectives







37

7.
1 Introduction








37

7
.2 Address Resolution Protocol (ARP)





37

7
.3 Reverse Address Resolution Protocol (RARP)




42

7.4 let us Sum Up








44

7.
5

Lesson end Activities







45

7.
6

Points for Discussion







45

7.
7

Check your progress







45

7.
8

Reference









45


Lesson 8.

Subnet Address and Multicast Address

8.0 Aims and Objectives







46

8
.1 Introduction








46

8.
2 Subnet Mask








47

8
.3 Multicast Addressing







48

8.4 Let
us Sum up








50

8.5
Lesson end Activities







51

8.6
Points for Discussion







51

8.7
Check your progress







51

8.8
Reference









51


Lesson 9.
Bootstrap and DHCP protocol

9.0

Aims and Objectives







52

9.1

Introduction








52

9.2
DHCP









52

9.3
Let Us Sum Up








54

9.4
Lesson and Activities







54

9.5
Points for Discussion







54

9.6
Check your progress







54

9.7
Reference









54



Lesson 10. Domain Name Service (DNS)

10.0

Aims and Objectives







55

10.1
Introduction








55

10.2
DNS protocol








57

10.3
Let us Sum Up








61

10.4
Lesson end Activities







61

10.5
Points for Discussion







61

10.6
Check Your Progress







61

10.7
Reference








61



Unit III

Lesson 11.
Internet Protocol (IP)

11.0
Aim
s
and Objective
s







62

11
.1 Introduction








62

11
.2 Datagrams








62

11.3 Le
t us Sum Up








65

11.4
Lesson end Activities







65

11.5
Points for Discussion







65

11.6
Check your Progress







65

11.7 Reference








65



Lesson 12.
The Internet Control Message Protocol (ICMP)

12.0 Aims and Objectives







66

12
.1 Introduction








66

12
.2. ICMP









66

12
.3 ICMP Messages








68

12.4 L
et us Sum Up








73

12.5
Lesson end Activities







73

12.6
Points for Discussion







73

12.7
Check your progress







73

12.8
Reference








73


Lesson 1
3
. Fragmentation and Reassembly


13. 0
Aim
s
and Objective
s







74

13
.1 Introduction








74

13
.
2
Fragmentation and Defragmentation





74

13.3
Let us Sum Up








76

13.4
Lesson end Activities







76

13.5
Points for Discussion







76

13.6
Check your Progress







76

13.7
Reference








77



Lesson 1
4
. Routing

14.0
Aim
s
and Objectives







78

14
.1 Introduction








78

14
.2 Routing









79

14
.3 Routing Protocol Vs Routed Protocol





79

14
.4 Types of routing table entries






80

14
.5 Classification of routing table






80

14.6
Let us Sum Up








82

14.7
Lesson end Activities







83

14.8
Points for Discussion







83

14.9
Check your Progress







83

14.10
Reference








83




Lesson 15
.
Distance Vector Protocol and Link State Routing Protocols


15.0 Aims and Objectives







84

15.1 Introduction








84

15.2 Distance Vector Routing Protocols





84

15.3 Link State Routing Protocols






85

15.4 Routing Information Protocol (RIP)





85

15.5 Open Shortest Path First (OSPF)





86

15.6 Let us Sum Up








87

15.7 Lesson end Activities







87

15.8 Points for Discussion







87

15.9 Check your Progress







88

15.10 Reference








88





Unit IV

Lesson 16.
TCP and UDP Data Structures

16.0
Aim
s
and Objectives







89

16.1
Introduction








89

16.
2 TCP Data Structures







89

16
.3 UDP Data Structures







92

16.4
Let us Sum Up








93

16.5
Lesson end Activities







94

16.6
Points for Discussion







94

16.7
Check your Progress







94

16.8
Reference








95




Lesson 17
. TCP Finite State Machine

17.0
Aim
s
and Objectives







96

17
.1 Introduction








96

17
.2 Algorithm for TCP state machine





96

17
.3 TCP finite state machine







97

17.4
Let us Sum Up








98

17.5
Lesson end Activities







98

17.6
Points for Discussion







98

17.7
Check your progress







98

17.8
Reference








98



Lesson 18. TCP Connection Management

18.0 Aim and Objectives







99

18.1 Introduction








99

18.2 Connection Extablishment






99

18.3

Connection Release







100

18.4 Let us Sum Up








102

18.5 Lesson end Activities







102

18.6 Points for Discussion







102

18.7 Reference








102




Lesson 19. TCP Output Processing

19.0 Aims and Objectives







104

19.1 Introduction








104

19.2 Timer Management







104

19.3 Packet Loss and Retransmission






105

19.4 Adaptive Retransmission






106

19.5 Flow Control








107

19.6 TCP Keep
-
Alive Messages






108

19.7 Slow Start Algorithm and Congestion Avoidance



109

19.8 Silly Window Syndrome (SWS)






109

19.9 Nagle Algorithm








109

19.10 TCP Selective Acknowledgment





109

19.11 Let us Sum Up








110

19.12 Lesson and Activities







111

19.13 Points for Discussion







111

19.14 Check your Progress







111

19.15 Reference








111



Lesson 20. Socket Programming

20.0


Aims and Objectives







112

20.1
Introduction








112

20
.2 Domain









112

20
.3 Internet address conversion






113

20
.
4
Connection less (UDP) Communication





116

20
.5 Connection oriented (TCP) Communication




116

20.6
Let us Sum Up








122

20.7
Lesson end Activities







125

20.8
Points for Discussion







125

20.9
Check your progress







125

20.10
Reference








125



Lesson 21. Application Layer

21.0 Ai
ms and Objectives







126

21.
1 Introduction








126

21
.2 Telnet









127

21
.3 Rlogin









133

21.4 Let us Sum Up








133

21.
5

Lesson end Activities







134

21.
6

Points for Discussion







134

21.
7

Check your Progress







134

21.
8

Reference








135






Lesson 22. File Transfer Protocol

22.0 Aims and Objectives







136

22.
1 Introduction








136

22
.2 File transfer protocol (FTP)






136

22
.3 Trivial File Transfer protocol (TFTP)





140

22.4 L
et us Sum Up








142

22.5 Lesson end Activities







143

22.6

Point for Discussion







143

22.
7

Check your Progress







143

22.
8

Reference








143


Lesson 23.
Email

23.0 Aims and Objectives







144

23
.1 Introduction








144

23
.2 Electronic Mail Addresses Scheme





144

23
.3 TCP/IP Standard for Electronic Mail Services




146

23
.4 Simple Mail Transfer Protocol (SMTP)





146

23
.5 Post Office Protocol (POP3)






149

23
.6 I
nternet Message Access Protocol (IMAP)




149

23.7
Let us Sum Up








150

23.8
Lesson end Activities







152

23.9
Points for Discussion







152

23.10
Check your progress







152

23.11
Reference








152



Lesson 24. Network Management System

24.0 Aims and Objectives







153

24
.1 Introduction








153

24
.2 Simple Network
Management Protocol





154

24.3
Let us Sum Up








157

24.4
Lesson and Activities







157

24.5
Point for Discussion







157

24.6
Check Your Progress







157

24.7 Reference








157


Lesson 2
5
.
X.25 Protocol

25.0 Aims and Objectives







158

25.
1 Introduction








158

25
.2 X.25 layers








158

25.3 Let us Sum Up








162

25.
4

Lesson end Activities







162

25.
5

Points for Discussion







162

25.
6

Check Your Progress







162

25.
7

Reference








163



Unit I

Lesson 1.
Introduction to Digital Communication


1.0

Aims and Objectives

1.2

Introduction to Data Communication

1.2 Classification of Computer Networks

1.3 Topology

1.4 Protocol

1.5 Internetworking Technologies

1.6 Let Us Sum Up

1.7 Lesson
-
end Activity

1.8 Points
for Discussion

1.9 Check your Progress

1.10
References


1.0
Aim
s
and Objective
s

To learn the concepts which is essential for Computer Networks


1.1
Introduction to Data Communication

The term telecommunication means communication at a distance. T
he word data refers to
information presented in whatever form is agreed upon by the parties creating and using the data.
Data communications are the exchange of data between two devices via some form of
transmission medium such as a wire cable.

Computer N
etwork

A network is a set of devices (often referred to as nodes) connected by communication
links. A node can be a computer, printer, or any other device capable of sending and/or receiving
data generated by other nodes on the network.

Software modules in
one system are used to communicate with one or more software
modules in the distance System. Such interfaces across a distance are termed as “peer
-
to
-
peer”
interfaces; and the local interfaces are termed as “service” interfaces. The modules on each end
ar
e organized as a sequence of functions called “layers”. The set of modules organized as layers
is also commonly called a “protocol stack”.

Over the years, some layered models have been standardized. The ISO Open Systems
Interconnection (ISO/OSI) layered mo
del has seven layers and was developed by a set of
committees under the auspices of International Standards Organization (ISO).

1.2 Classification of Computer Networks


Based on Transmission Mode

Transmission mode defines the direction of signal flow betwe
en two linked devices.
There are three types of transmission modes.


Simplex

In simplex mode, the communication is unidirectional. Among the stations only one can
transmit and the other can only receive.


Half
-
Duplex


In half
-
Duplex mode, the communication
is bidirectional. In this both station can sent and
receive but not at the same time.


Full
-
Duplex


In Full
-
Duplex mode, both stations can transmit and receive simultaneously.



Based on Time in Transmission Type


Synchronous Transmission

In synchronous
Transmission both the sender and the receiver use the same time cycle for
the transmission. We send bits one after another without start/stop bits or gaps. It is the
responsibility of the receiver to group the bits. Bit stream is delivered with a fixed del
ay
and given error rate. Each bit reaches the destination with the same time delay after
leaving the source.


Asynchronous Transmission

In Asynchronous Transmission we send one start bit at the beginning and one stop bit at
the end of each byte. There may
be a gap between each byte. Bit stream is divided into
packets. Packets are received with varying delays, so packets can arrive out of order.
Some packets are not received correctly.


Based on Authentication




Peer to Peer Connection



In peer
-
to
-
p
eer networks, there are no dedicated servers. All

the computers are
equal and, therefore, are termed as peers. Normally, each computer functions as both a
client and a server. No one can control the other computers.





Server Based Connection



Most networks have a dedicated server. A dedicated server is a computer on a network
which functions as a server, and cannot be used as a client or a workstation. A dedicated
server is optimized to service requests from network clients. A server can con
trol the
clients for its services.


Based on Geographical location




LAN (Local Area Network)

Networks which cover close geographical area. LAN used to link the devices in a single
office, building or campus. It provides high speeds over short dis
tance. Systems are
connecting directly to Network. The LAN is owned by private people.





MAN (Metropolitan Area Network)


Metropolitan area network is an extension of local area network to spread over the city. It
may be a single network or a ne
twork in which more than one local area network can
share their resources.





WAN (Wide Area Network)

WAN spread over the world may be spread over more than one city country or continent.
Systems in this network are connected indirectly. Generally
WAN network are slower
speed than LAN’s. The WAN network are owned or operated by network providers. If it
is owned by a single owner then it is called Enterprise network. Often these types have
combination of more than one topology.



Based on Reliabilit
y


Reliability is maintained by authentication.


Connection
-
oriented




This type of communication establishes a session connection before data can be sent.
This method is often called a "reliable" network service. It can guarantee that data will
arrive in
the same order.



Connection less


This type of communication does not require a session connection between sender and
receiver for data transfer. The sender simply starts sending packets to the destination. A
connectionless network provides minimal services.



1.3 Topology

Topology

refers to physical layout including computers, cables, and other resources; it
determines how components communicate with each other.


Today’s network designs are based on three topologies:

Bus
consists of series of computers connected along a single cabl
e segment

Star
connects computers via central connection point or hub

Ring
connects computers to form a loop


All computers, regardless of topology, communicate by addressing data to one or more
computers and transmitting it across cable as electronic sign
als. Data is broken into
packets
and
sent as electronic signals that travel on the cable. Only the computer to which the data is
addressed accepts it.




1.4 Protocol

Protocols mean set of rules. It is a formal description of message formats and the rules
two or
more machines has follow to exchange messages. The key elements of a protocol are syntax,
semantics and timing.


Syntax

Syntax refers to the structure or format of the data, meaning the order in which they are
presented.


Semantics

Semantics refers to the meaning of each section of bits.


Timing

Timing refers to when data should be sent and how fast it can be sent.



1.5 Internetworking Technologies


Internetworking Technologies tell how the Internet accommodating multiple underlying

hardware technologies and how they are interconnected and formed the network, and set of
communication standard which the network used to interoperate.


The lowercase internet means multiple networks connected together, using a common
protocol suite. The
uppercase Internet refers to the collection of hosts around the world that can
communicate with each other using TCP/IP. While the Internet is an internet, the reverse is not
true.


1.6 Let us Sum up

Data Communication

The term telecommunication means com
munication at a distance.

Computer Network

A network is a set of devices (often referred to as nodes) connected by communication
links.

Classification of Computer Networks

Based on Transmission Mode

Simplex

In simplex mode, the communication is unidirectional.

Half
-
Duplex



In half
-
Duplex mode, the communication is bidirectional.

Full
-
Duplex



In Full
-
Duplex mode, both stations can transmit and receive simultaneously.



Based on Transmission Mode

Synchrono
us Transmission


Each bit reaches the destination with the same time delay after leaving the source.

Asynchronous Transmission

Packets are received with varying delays, so packets can arrive out of order. Some
packets are not received correctly.

Based on
Authentication



Peer to Peer Connection

In peer
-
to
-
peer networks, there are no dedicated servers. No one can control the other
computers.



Server Based Connection


A dedicated server is optimized to service requests from network clients.
A server can
control the clients for its services.



Based on Geographical location



LAN (Local Area Network)

Networks which cover close geographical area



MAN (Metropolitan Area Network)


Metropolitan area network is an extension of local area network to spread over the city.




WAN (Wide Area Network)

WAN spread over the world may be spread over more than one city country or continent.




Based on Reliability

Connection
-
oriented



It can guarantee that data will arrive in the same order.


Connection less

This type of communication does not require a session connection between sender and
receiver for data transfer. The sender simply starts sending packets to the destination.


T
opology

Topology

refers to physical layout including computers, cables, and other resources

Bus
consists of series of computers connected along a single cable segment

Star
connects computers via central connection point or hub

Ring
connects compu
ters to form a loop


Protocol

Protocols mean set of rules

Syntax

Syntax refers to the structure or format of the data, meaning the order in which they are
presented.

Semantics

Semantics refers to the meaning of each section of bits.


Timing

Timing refers
to when data should be sent and how fast it can be sent.


Internetworking Technologies

Network of Inter connected Networks
.

1.7
Lesson
-
end Activities

1.

What is telecommunication?

2.

What is Computer Network?


1.8
Points for Discussion

1.

What are the classifications of Computer Networks.?

1.9
Check you Progress

1.

What is topology? Write short notes on different topology. What are the advantages and
disadvantages of this topology?

2.

What is protocol? What are the elements of protocol?



1
.10 References


1.

“ Internetworking with TCP/IP Principles, Protocols, and Architecture Volume I”,
Douglas E. Comer, Prentice Hall of India Pvt. Ltd,

2.

“Computer Networks”, Andrew S. Tanenbaum, Prentice Hall of India Pvt. Ltd.

3.

“Introduction to Data
Communications and Networking”, Behrouz Forouzan, McGraq
-
Hill

4.


MCSE Networking Essentials Study Guide”, Duncan Anderson, Tata McGraw
-
Hill

Lesson 2
.
WAN Technology

2.0
Aims and Objectives

2.1 Introduction

2.2 WAN Networking Devices

2
.3 WAN Protocols

2.4 Let us Sum Up

2.5 Lesson end Activities

2.6 Points for Discussion

2.7 References


2.0 Aims and Objectives


To learn the devices which are used in WAN


To learn the Protocols which are used in WAN

2.1 Introduction

LAN (Local Area Network) network spread
for close geographical area. It provides high
speeds over short distance. In this network all the systems must connect directly to network. In
WAN (Wide Area Network) the network can be far apart. In this network systems are connected
indirectly. This net
work generally slower speed than LAN’s.

Another way to connect networks is with a
bridge.
These connect networks at the link
layer, while routers connect networks at the network layer. Bridges makes multiple LANs appear
to the upper layers as a single LAN.



2.2 WAN Networking Devices


Repeaters


A repeater is a device that regenerates signals so that the signal can travel on addition
cable segments. They do not translate or filter data. Repeater is used to connect two networks
that use the same technology
. It receives every data packet on each network, and retransmits it
onto the other network. The net result is that the two networks have exactly the same set of
packets on them.


Its primary purpose is to get around limitations in cable length caused by
signal loss or
timing dispersion. For a repeater to function, both segments which the repeater joins must have
the same media access scheme, protocol and transmission technique.



Repeaters can move packets from one medium to another. Some multiport repea
ters can
connect different types of media. Repeaters improve performance by dividing the network into
segments, thus reducing the number of computers per segment.



Bridge

Bridge is a device that can join two LANs. However, bridg
e can also divide an
overloaded network into separate networks, reducing the traffic on each segment and making
each network more efficient.




A bridge can link unlike physical media such as twisted
-
pair and coaxial Ethernet. It can
also link unlike net
work segments such as Ethernet and Token Ring.



A bridge can be installed internally or if the destination address is not listed in the routing
table, the bridge forwards the packets to all segments. Multiple bridges can be used to combine
several extern
ally. Bridges are faster than routers because routers perform complex functions on
each packet.



Switches

Switches allow different nodes of a network to communicate directly with each other in a
smooth and efficient manner. Switches are divided into two
types Store and Forward and Cut
Through. Store and Forward switches stores the details and forwarded to the respective system.
In the Cut through switches it just forward the details to the respective systems.


Routers


A router is a device used to connec
t networks that use different architectures and
protocols. They can switch and transfer information packets across multiple networks. This
process is called routing. They can determine the best path for sending data and filters broadcast
traffic, to the l
ocal segment. Routers cannot link to remote computers. They can read only
addressed network packets. Routers can link segments that use different data packaging and
media schemes.


Gateways


Gateways make communication possible between systems that use d
ifferent
communication protocols, data formatting structures, languages and architectures. Gateways
repackage data going from one system to another. Gateways are usually dedicated servers on a
network and are task
-
specific.











2.3 WAN Protocols

Frame Relay

Frame relay is used to connect large number of sites in the network because it is
relatively inexpensive to do so. The service provider gives you a frame relay circuit and is
charged for the amount of data and the bandwidth you use as oppose to
T1 circuit that charges
with a flat monthly rate whether you use partial bandwidth or the full bandwidth regardless.
Frame relay is a high performance WAN protocol that operates at the Data Link layer and the
Physical layer of the OSI model.


Integrated S
ervices Digital Network (ISDN)

Integrated Services Digital Network (ISDN) is designed to run over existing telephone
networks. It can deliver end to end digital service carrying voice and data. ISDN operates at OSI
model, physical layer, data link layer an
d network layer. It can carry multimedia and graphics
with all other voice, data services. ISDN supports all upper layer protocols and you can choose
PPP, HDLC or LAPD as your encapsulation protocol. It has two offerings, Primary rate which is
23B+D channe
ls. 23, 64 kbps and one 64kbps mainly used for signaling. The other is the Basic
Rate which has 2B+D channels two 64kbps and one 16kbps.

At data link layer ISDN supports two protocols; LAPB and LAPD. LAPB is used to
mainly transfer data from upper layers
and has three types of frames. I
-
Frames carry upper layer
information and carries out sequencing, flow control, error detection and recovery. S
-
Frames
carry control information for the I
-
frame. LAPD provides an additional multiplexing function to
the uppe
r layers enabling number of network entities to operate over a single physical access.
Each individual link procedure acts independently of others. The multiplex procedure combines
and distributes the data link channels according to the address information
of the frame. Each
link is associated with a specific Service Access Point (SAP), which is identified in the part of
the address field.


High Level Data Link Control (HDLC)

High Level Data Link Control (HDLC) is a bit oriented data link layer frame protoc
ol
that has many versions similar to LAP, LAPB, and LAPD. CISCO routers default encapsulation
is HDLC, but it is proprietary to CISCO.



Point to Point Protocol (PPP)

Point to Point Protocol (PPP) is a Data Link Layer protocol that can be used over ether
a
synchronous (dial up) or synchronous (ISDN) lines. It uses Link Control Protocol (LCP) to
build and maintain data link connections. Included in PPP is the authentication protocols, PAP
and CHAP, and data compression. It supports IP, IPX, AppleTalk, DECnet
and OSI/CLNS.


2.4
Let us Sum Up


WAN Networking Devices


Repeaters

A repeater is a device that regenerates signals so that the signal can travel on addition
cable segments.


Bridge

Bridge is a device that can join two LANs.


Switches

Switches allow different nodes of a network to communicate directly with each other in a
smooth and efficient manner.


Routers


A router is a device used to connect networks that use different architectures and
protocols.


Gateways


Gateways make communication possible between systems that use different
communication protocols, data formatting structures, languages and architectures.




WAN Protocols

Frame Relay

Frame relay is used to connect large number of sites in the network be
cause it is
relatively inexpensive to do so. The service provider gives you a frame relay circuit and is
charged for the amount of data and the bandwidth you use as oppose to T1 circuit that charges
with a flat monthly rate whether you use partial bandwidt
h or the full bandwidth regardless.



Integrated Services Digital Network (ISDN)

Integrated Services Digital Network (ISDN) is designed to run over existing telephone
networks.

High Level Data Link Control (HDLC)

High Level Data Link Control (HDLC) is a
bit oriented data link layer frame protocol
that has many versions similar to LAP, LAPB, and LAPD.

Point to Point Protocol (PPP)

Point to Point Protocol (PPP) is a Data Link Layer protocol that can be used over ether
asynchronous (dial up) or synchronous
(ISDN) lines.

2.5 Lesson End Activities

1.

When we need Repeater and when we need Bridge?

2.

How the Gateway is different from the Router?

2.6 Points for Discussion

1.

What is the difference between Switch and Hub?

2.7 Check Your Progress

Write short notes on

o

Repeater

o

Bridge

o

Switch

o

Router

o

Gateways

o

ISDN and HDLC


2.8 References


1.

“ Internetworking with TCP/IP Principles, Protocols, and Architecture Volume I”,
Douglas E. Comer, Prentice Hall of India Pvt. Ltd,

2.


Computer Networks”, Andrew S. Tanenbaum, Prentice Hall of India Pvt. Ltd.

3.

“Introduction to Data Communications and Networking”, Behrouz Forouzan, McGraq
-
Hill

4.

“MCSE Networking Essentials Study Guide”, Duncan Anderson, Tata McGraw
-
Hill


Lesson
3
.
Histo
ry about TCP/IP


3.0 Aims and Objectives

3.1 Introduction

3.2 Internet Society

3.3 Request For Comments (RFC)

3.4
Let Us Sum Up

3.5
Lesson End Activities

3.6
Points for Discussion

3.7
Check your progress

3.8 References


3.0 Aims and
Objective



To learn the history about TCP/IP




3.1 Introduction


TCP/IP is a set of protocols developed to allow cooperating computers to share resources
across a network.



In 1969 the Defense Advanced research projects Agency (DARPA) funded a research
and development project to create an experimental packet switching network. This network is
called ARPANET. In 1975 the ARPANET was converted from an experimental network to a
n
operational network, and the responsibility for administering the network was given to the
Defense Communication Agency (DCA).


The TCP/IP protocols were adopted as Military Standards (MIL STD) in 1983, and all
hosts connected to the network were require
d to convert to the new protocols. DARPA funded to
implement TCP/IP in Berkely Unix.


In 1983, the old ARPANET was divided into MILNET and smaller ARPANET. The
Internet was used to refer to the entire network; MILNET and ARPANET.

Advantages of TCP/IP

Open
protocol standards, freely available and developed independently from any specific
computer hardware or operating system. A common addressing scheme which is e
nable to
connect the most widely used networks. It may use any protocols.
It c
onnects dissimilar systems.

It p
rovides client/server framework.
It p
rovides access to the Internet


Differences of the OSI and TCP/IP models


TCP/IP combines the presentation and session layer into its application layer
.
TCP/IP
combines the OSI data link
and physical layers into one layer
.
TCP/IP appears simpler because it
has fewer layers
.
TCP/IP transport layer using UDP does not always guarantee reliable delivery
of packets as the transport layer in the OSI model does
.



3.
2
Internet Society

The Internet Society (ISOC) is a professional society to facilitate, support, and promote
the evolution and growth of the Internet as a global research communications infrastructure.


3.
3
Request For Comments (RFC)

Documentation about TCP/IP protocols, st
andards, and policies are available in the on
-
line repositories without any charge. The RFC series is numbered sequentially in the
chronological order RFCs are written.

Even though Internet is a common public one for organizing administrative activities th
ey
have different committees. They are :


Internet Architecture Board (IAB)

The Internet Architecture Board (IAB) is the technical oversight and coordination body.
It is composed of about 15 international volunteers from various disciplines and serves as t
he
final editorial and technical review board for the quality of Internet standards. The IAB falls
under the ISOC.

Internet Engineering Task Force (IETF)

The Internet Engineering Task Force (IETF) is the near
-
term, standards
-
oriented group,
divided into n
ine areas (applications, routing and addressing, security, etc.). The IETF develops
the specifications that become Internet standards. An additional Internet Engineering Steering
Group (IESG) was formed to help the IETF chair.

Internet Research Task Force
(IRTF)

The Internet Research Task Force (IRTF) pursues long
-
term research projects.



3.4
Let us Sum Up


In 1969 the Defense Advanced research projects Agency (DARPA) funded a research
and development project to create an experimental packet switching ne
twork. This network is
called ARPANET.


In 1983, the old ARPANET was divided into MILNET and smaller ARPANET. The
Internet was used to refer to the entire network; MILNET and ARPANET.

Request For Comments (RFC)


Documentation about TCP/IP protocols, standards, and policies are available in the on
-
line repositories without any charge. The RFC series is numbered sequentially in the
chronological order RFCs are written.

Advantages of TCP/IP

A common addressing

It m
ay use any protocols.


It c
onnects dissimilar systems.


It p
rovides client/server framework.


It p
rovides access to the Internet


Internet Architecture Board (IAB)

The Internet Architecture Board (IAB) is the technical oversight and coordination body..

In
ternet Engineering Task Force (IETF)

The Internet Engineering Task Force (IETF) is the near
-
term, standards
-
oriented group,
divided into nine areas (applications, routing and addressing, security, etc.).

Internet Research Task Force (IRTF)

The Internet Re
search Task Force (IRTF) pursues long
-
term research projects.

3.5
Lesson end Activities

1. When the TCP/IP project started and by whom?


3.6
Points for Discussion

1.

What are the governing bodies involved in Internet Organisations?

3.7
Check your progress

1.

What is the purpose of RFC?

2.

Write the difference between OSI and TCP/IP layer.

3.

How Internet is organized?

3.8
References


1.

“ Internetworking with TCP/IP Principles, Protocols, and Architecture Volume I”,
Douglas E. Comer, Prentice Hall of I
ndia Pvt. Ltd,

2.

“Computer Networks”, Andrew S. Tanenbaum, Prentice Hall of India Pvt. Ltd.

3.

“Introduction to Data Communications and Networking”, Behrouz Forouzan, McGraq
-
Hill

4.

“MCSE Networking Essentials Study Guide”
, Duncan Anderson, Tata McGraw
-
Hill



Lesson 4. TCP/IP layer Architecture

4.0 Aims and Objectives

4.1 Introduction

4.2 Internet Architecture

4.3 TCP/IP layer Architecture

4.4
Let us Sum Up

4.5
Points for Discussion

4.6
Check your progress


4.0 Aims and
Objective
s


To learn the architecture and layer and their functions of TCP/IP


4.1 Introduction


Each layer contains logical groupings of functions that provide specific services for
facilitating a communication. A function, or a group of functions, making
up a functional unit is
a logical entity that accepts one or more inputs (arguments) and produces a single output (value)
determined by the nature of the function. Functions can be grouped in a collective unit, which is
then defined as (N) layer having (N
+1) layer an upper layer boundary and (N
-
1) layer as a lower
boundary. The N layer receives services from N
-
1 layer and provides services to N+1 layer.


4.2 Internet Architecture

A few stand
-
alone systems were collected together into a network. People are
combining
multiple networks together into an internetwork, or an internet. An internet is a collection of
networks that all use the same protocol suite.

The easiest way to build an internet is to connect two or more networks with a router.
This is often
a special
-
purpose hardware box for connecting networks. The following diagram
shows that two networks connected and form an Internet.



Figure
4.
1 : Simple Internet


Two computers, anywhere in the world
, following certain hardware, software, protocol
specifications, can communicate, reliably even when not directly connected. LANs are no longer
scalable beyond a certain number of stations or geographic separation.

4.3 TCP/IP layer Architecture

There is no standard for layers in TCP/IP. Some refers as 5 layers including physical
layer and some may refer four layers. The four layered structure of TCP/IP is seen in the way
data is handled as it passes down the protocol stack from the Application La
yer to the underlying
physical network. Each layer in the stack adds control information to ensure proper delivery.
This control information is called a header because it is placed in front of the data to be
transmitted. Each layer treats all of the inform
ation it received from the layer above as data and
places its own header in front of that information. The addition of delivery information at every
layer is called encapsulation. When data is received each layer strips off its header before passing
the da
ta on to the layer above.


Each layer has its own data structures and terminology to describe that structure. In
application layer the TCP data is called stream where as in the UDP it is called message. In the
transport layer the data is called segment wh
ere as in the UDP it is called packet. In the Internet
layer both TCP and UDP data are called as datagrams. In the network access layer both TCP and
UDP data are called frame.


Application
Transport
Internet
Network Access


Figure 4.2 TCP/IP layers

Network Access layer


The TCP/IP Network Access layer can encompass the functions of all three lower layers
of the OSI
References
Model (Network, Data Link and Physical). As new hardware technologies
appear new Network Access protocols must be developed so
that TCP/IP networks can use the
new hardware.

Functions


Addressing scheme

For this it provide a protocol called Address Resolution Protocol (ARP) defined
in the RFC 826..


Transmission of IP datagram over Ethernet network

This specifies how IP datagra
ms are encapsulated for transmission over Ethernet
networks.


Header Encapsulation







Figure 4.3 TCP/IP Encapsulation


When an application sends data using TCP, the data is sent down the protocol stack,
through e
ach layer, until it is sent as a stream of bits across the network. Each layer adds
information to the data by prepending headers (and sometimes adding trailer information) to the
data that it receives. Figure 1.4.3 shows this process. The unit of data tha
t TCP sends to IP is
called a TCP segment. The unit of data that IP sends to the network interface is called an IP
datagram. The stream of bits that flows across the Ethernet is called a frame.

Internet layer


All TCP/IP communication data are flow through
IP regardless of its final destination. It
provides basic packet delivery service. The important protocol in this layer is Internet Protocol
defined in RFC 791.

Function of Internet Protocol


Defining the datagram, this is the basic unit of transmission in the Internet.


Defining the Internet addressing scheme.


Routing datagrams to remote hosts


Performing fragmentation and reassembly of datagrams


IP is a connectionless protocol. IP does not
exchange control information to establish an
end
-
to
-
end connection before transmitting data. It also called unreliable protocol because it
contains no error detection and recovery code.

Routing Datagrams


Gateways are devices that switch packets between th
e different physical networks.
Deciding which gateway to use is called routing. IP makes the routing decision for each
individual packet.


Internet gateways are commonly referred to IP routers because they use Internet Protocol
to route packets between net
works.


Host 1
Application
Transport
Internet
Network
Network
Internet
Transport
Internet
Network
Application
Host 2
Gateway 2
Gateway 1
Network A
Network B
Network C
Internet
Network


Figure
4.
4 Routing Through Gateways



The uses of gateways are to forward packets. The hosts process packets through all four
protocol layers, while the gateways process the packets only up to the Internet
layer where the
routing decisions are made.

Fragmenting datagrams


Datagrams may routed through different networks. Each type of network has a Maximum
Transmission Unit (MTU), which is the largest packet that it can transfer. If the datagram
received from
one network may be too large to be transmitted in a single packet on a different
network. In this case, IP module in a gateway is to divide the datagram into smaller pieces.
This process is called fragmentation.

Transport layer

Transport Layer has tw
o important protocols for connection oriented and connection less
services. They are TCP and UDP. TCP (Transmission Control Protocol) provides a connection
-
oriented, reliable, byte stream service (RFC793). TCP is an independent, general purpose
protocol th
at can be adapted for use with delivery systems other than IP. A stream of 8
-
bit bytes
is exchanged across a TCP connection. UDP (User Datagram Protocol) is a simple, unreliable,
datagram
-
oriented, transport layer protocol (RFC768).



Application Layer

Top
of the TCP/IP architecture layer is Application Layer. It contains collection of
services. Each service can be identified by their number called port number. Each service is
defined by separate protocol and has their separate RFC. Eg. FTP. Telnet


4.4 Let us Sum Up


TCP/IP layer Architecture

Network Access layer
-
Functions


Addressing scheme


Transmission of IP datagram over Ethernet network


Internet layer


Function of Internet Protocol


Defining the datagram, this is the basic unit of transmissi
on in the Internet.


Defining the Internet addressing scheme.


Routing datagrams to remote hosts


Performing fragmentation and reassembly of datagrams

IP is a connectionless protocol


Routing Datagrams


Gateways are devices that switch packets between the
different physical networks.
Deciding which gateway to use is called routing.



Fragmenting datagrams


Datagrams. Each type of network has a Maximum Transmission Unit (MTU), which is
the largest packet that it can transfer. If the datagram received from on
e network may be too
large to be transmitted in a single packet on a different network. In this case, IP module in a
gateway to divide the datagram into smaller pieces. This process is called fragmentation.

Transport layer

TCP (Trans
mission Control Protocol) provides a connection
-
oriented, reliable, byte
stream service. UDP (User Datagram Protocol) is a simple, unreliable, datagram
-
oriented,
transport layer protocol (RFC768).

Application Layer

Top of the TCP/IP architecture layer is A
pplication Layer. It contains collection of
services.


4.5
Lesson end Activities

1.

What is the purpose of Internet Architecture Board?


4.6
Points for Discussion

1.

What is Header Encapsulation and Decapsulation?


4.7
Check your Progress

1.

What are layers available in TCP/IP?

2.

What is the function of Network layer?

3.

What is the function of IP layer?

4.

What is the function of Transport layer?


4.8 References


1.

“ Internetworking with TCP/IP Principles, Protocols, and Architecture Volu
me I”,
Douglas E. Comer, Prentice Hall of India Pvt. Ltd,

2.

“Computer Networks”, Andrew S. Tanenbaum, Prentice Hall of India Pvt. Ltd.

3.

“Introduction to Data Communications and Networking”, Behrouz Forouzan, McGraq
-
Hill

4.


MCSE Networking Essentials Study Guide”, Duncan Anderson, Tata McGraw
-
Hill

Lesson 5. Network Interface

5.0 Aims and Objectives

5.1 Introduction

5.2 Network Interface Card

5.3 Cable type and Specification Type

5.4 Other Protocols

5.5
Let us Sum Up

5.6
Le
sson end Activities

5.7
Points for Discussion

5.8
Check you Progress

5.9 References



5.0
Aim
s
and Objective
s


To learn about Network interface Device and their function

5.1 Introduction

The purpose of the network interface layer is it handles the details
of the communication
media (Ethernet, token ring, etc.)


5.2 Network Interface Card


A network interface card is used to connect a computer to an Ethernet network. The card
(shown in the figure below) provides an interface to the media. This may be eithe
r using an
external transceiver (as shown) or through an internal integrated transceiver mounted on the
network interface card PCB. The card usually also contains the protocol control firmware and
Ethernet Controller needed to support the Medium Access C
ontrol (MAC) data link protocol.




Figure 5.1 Network Interface Card (NIC)



The Ethernet


Most of our networks these days use Ethernet also called Network Interface Card(NIC).
Ethernet has its own Addressing sch
eme. No two machines have the same Ethernet address. This
is a unique number issued by IEEE to the manufacturer. So each Ethernet controller comes with
an address built in from the factory. The address consists of 48 bits. First 24 bits represents the
ven
dor and next 24 bits represents the serial number of the NIC card. This hardware address is
used by the Media Access Control (MAC) layer of the Data Link layer to identify uniquely, the
LAN device, to the network layer.


Ethernet equipment manufacturers have to register with a central authority, to make sure
that the numbers they assign don't overlap any other manufacturer. Ethernet is a "broadcast
medium". When you send a packet out on the Ethernet, every machine on t
he network sees the
packet. So something is needed to make sure that the right machine gets it. Every Ethernet
packet has a 14
-
octet header that includes the source and destination Ethernet address, and a type
code.




Figure 5.2 Ethernet Data format



Each machine is supposed to pay attention only to packets with its own Ethernet address
in the destination field. Each machine has to have a table of what Ethernet address corresponds
to what Internet address. In ad
dition to the addresses, the header contains a type code. The type
code is to allow for several different protocol families to be used on the same network. So you
can use TCP/IP, DECnet, Xerox NS, etc., at the same time. Each of them will put a differe
nt
value in the type field. Finally, there is a checksum. The Ethernet controller computes a
checksum of the entire packet. When the other end receives the packet, it recomputes the
checksum, and throws the packet away if the answer disagrees with
the original. The checksum
is put on the end of the packet, not in the header.


The original Ethernet was developed as an experimental coaxial cable
network in the 1970s
by Xerox Corporation to operate with a data rate of 3 Mbps using a carrier sense multiple access
collision detect (CSMA/CD) protocol for LANs with sporadic but occasionally heavy traffic
requirements.


IEEE Specification for Ethernet



802.3


Ethernet LAN specification



802.3u

Fast Ethernet



802.3z


Gigabit Ethernet



Ethernet card is an add on card which needed for the computers which connected to the
network. Computers which used as a stand alone system need not have Ethernet
card. The
following figure shows the sample Ethernet card.




Figure 5.3 Ethernet Card





5.3 Cable type and Specification Type



Ethernet support different types of cables, each have their own specification and
transmission distance. These are given in the following table.


220 meters
Unshielded Twisted Pair
100BaseTX
100 meters
Unshielded Twisted Pair
100BaseT
2000 meters
Fiber Optic
10BaseF
500 meters
Thick Coaxial
10Base5
185 meters
Thin Coaxial
10Base2
100 meters
Unshielded Twisted Pair
10BaseT
Maximum length
Cable Type
Specification
220 meters
Unshielded Twisted Pair
100BaseTX
100 meters
Unshielded Twisted Pair
100BaseT
2000 meters
Fiber Optic
10BaseF
500 meters
Thick Coaxial
10Base5
185 meters
Thin Coaxial
10Base2
100 meters
Unshielded Twisted Pair
10BaseT
Maximum length
Cable Type
Specification


5.4 Other Protocols

Serial Line IP (SLIP)

SLIP stands for Se
rial Line IP. It is a simple form of encapsulation for IP datagrams on
serial lines, and is specified in RFC 1055. SLIP has become popular for connecting home
systems to the Internet, through the ubiquitous RS
-
232 serial port found on almost every
computer
and high
-
speed modems.

Point
-
to
-
Point Protocol (PPP)

PPP,
the Point
-
to
-
Point Protocol, corrects all the deficiencies in SLIP. PPP consists of
three components.

A way to encapsulate IP datagrams on a serial link. PPP su
pports either an asynchronous
link with 8 bits of data and no parity (i.e., the ubiquitous serial interface found on most
computers) or bit
-
oriented synchronous links.

A link control protocol
(LCP)
to establish, configure, an
d test the data
-
link connection.
This allows each end to negotiate various options.

A family of network control protocols
(NCPs)
specific to different network layer
protocols.
RFCs
currently exis
t for IP, the
OSI
network layer,
DECnet,
and
AppleTalk.
The IP
NCP,
for example, allows each end to specify if it can perform header com
pression, similar to
CSLIP.


RFC
1548
[
specifies the encapsulation method and the link control protocol. RFC 1332
specifies the network control protocol for IP.


Loopback Interface

Most implementations support a loopback interface that allows a client and server on the
same host to communicate with each other using TCP/IP. The class A network ID 127 is
reserved for the loopback interface. By convention, most sys
tems assign the IP address of
127.0.0.1 to this interface and assign it the name
localhost
.
An IP datagram sent to the
loopback interface must not appear on any network.


5.5
Let Us Sum Up

Network Interface Card


A network interface card is used to connect a computer to an Ethernet network. The card
(shown in the figure below) provides an interface to the media.


IEEE Specification for Ethernet



802.3


Ethernet LAN specification



802.3u

Fast Ethernet



802.3z



Gigabit Ethernet


Serial Line IP (SLIP)

SLIP stands for Serial Line IP. It is a simple form of encapsulation for IP datagrams on
serial lines

Loopback Interface

Most implementations support a loopback interface that allows a client and server on the
sam
e host to communicate with each other using TCP/IP.


5.6
Lesson end Activities

Discuss different type of Cable types.


5.7
Points to Discussion


How Ethernet card is connected to the PC?


5.8
Check your progress

1.

What is the purpose of Network Interface
card?

2.

How Ethernet is working?

(or) Explain the functionality of Ethernet with a neat figure.

3.

Write Short Notes on: a) SLIP, b) PPP



5.9 References


1.


Internetworking with TCP/IP Principles, Protocols, and Architecture Volume I”,
Douglas E. Comer, Prentice Hall of India Pvt. Ltd,

2.

“Computer Networks”, Andrew S. Tanenbaum, Prentice Hall of India Pvt. Ltd.

3.

“Introduction to Data Communications and
Networking”, Behrouz Forouzan, McGraq
-
Hill

4.

“MCSE Networking Essentials Study Guide”, Duncan Anderson, Tata McGraw
-
Hill


Unit II

Lesson 6.
IP Addressing Scheme

6.0 Aims and Objectives

6
.1 Introduction

6
.2 Classful Address

6
.3 Special Address

6
.4 Classle
ss Inter
-
Domain Routing (CIDR)

6
.5 Multihoming

6.6
Let us Sum Up

6.7
Lesson end Activities

6.8
Points for Discussion

6.9
Check your progress

6.10 References


6.0
Aim
s
and Objective
s

To learn the TCP/IP addressing schemes

6
.1 Introduction

There are three types of IP addresses:
unicast
(destined for a single host),
broadcast
(destined for all hosts on a given network), and
multicast
(destined for a set of hosts that belong
to a multicast group).


IP Addressing Scheme



Universal Service
-
al
l computers on all physically different networks can communicate.



Physical addresses
-
allow communication between computers on one network.



The IP address
-
provides virtual addressing. The address is software controlled, whereas
the address for the n
etwork card is hardware based.


The IP addressing scheme is quite complex, and there have been many revisions to the IP
scheme. The IANA, InterNIC, and ARIN work together to subdivide and issue addresses for
Internet clients. You can subdivide addresses as
signed by InterNIC. Routing tables can be
created manually and dynamically. IP addressing schemes allows for seamless integration
amongst heterogeneous networks. To send a packet, the destination IP address of the computer is
used not the hardware address
. This allows for communication across networks.

The IP address is 32 bits in length (IPv4) and contains sequence of 1s and 0s. The IP
addresses are divided into a prefix and suffix. The suffix is the host address. The prefix is the
network number. The address space of IPv4 is 232 or 4,294,967,296.


6
.
2 Classful Address

In classful addressing, the address space is divided into five classes: A, B, C, D, and E
to
define large, medium, and small networks. The Class D address class was created to enable
multicasting. IETF reserves Class E addresses for its
own research.
To make the IP address
easier to use, the address is usually written as four decimal numbers separated by periods. This
way of writing the address is called the dotted decimal format.

Eg.

Numbers 0.0.0.0 through 255.255.255.255

It is much
better than reading

10000001 00110100 00000110 00000000

Dotted
-
decimal notation and binary notation for an IPv4 address shown in the following
diagram:


Figure
6
.1 Dotted decimal notation and binary notation



Figure
6
.2 Classes in binary and dotted
-
decimal notation

Dotted Decimal with Classes



Class A:



1 prefix octet (128 networks)



3 suffix octets (16777216 hosts)



Class B:



2 prefix octets (16384 networks)



2 suffix octets (65536 hosts)




Class C:



3 prefix octets (2097152 networks)



1 suffix octet (256 hosts)


Number of blocks and block size in classful IPv4 addressing shown bellow:



Figure
6
.3 Classful address
block size


No two machines that connect to a public network can have the same IP address because
public IP addresses are global and standardized. A central authority exists for IP address
delegation. In the US, it’s ARIN

American Registry for Internet
Numbers. People just can’t
arbitrarily use any IP network if their network is publicly accessible. That would lead to routing
conflicts.

Classful addressing, which is almost obsolete, is replaced with classless addressing. The
first address in a block is n
ormally not assigned to any device; it is used as the network address
that represents the organization to the rest of the world.

The first address in the block can be found by setting the rightmost 32


n
bits to 0s. The
last address in the block can be f
ound by setting the rightmost 32

n bits to 1s. The number of
addresses in the block can be found by using the formula 232

n.

Private IP addresses

Private IP addresses are a solution to the problem of the exhaustion of public IP
addresses. Addresses that
fall within these ranges are not routed on the Internet backbone. It is
described in
RFC 1597.



10.0.0.0


10.255.255.255 (Full Class A)



172.16.0.0


172.31.255.255 (16 Class B’s)



192.168.0.0


192.168.255.255 (Full Class B)



Figure
6
.4 Private classful address and their ranges


6
.3 Special Address


Network addresses 0 and 127 are reserved for special uses. Network 0 designates the
default route. The default route is used to simplify the routing
information that IP must handle.
Network address 127 is loop back address. The loop back address simplifies network
applications by allowing the local host to be addressed in the same manner as remote host. An IP
address with all bits set to one is a broa
dcast address. A broadcast address is used to
simultaneously address every host on a network.

0 is reserved for machines that don't know their address. In certain circumstances it is
possible for a machine not to know the number of the network it is on, o
r even its own host
address. For example, 0.0.0.23 would be a machine that knew it was host number 23, but didn't
know on what network.


255 is used for "broadcast". A broadcast is a message that you want every system on
the network to see. Broadcas
ts are used in some situations where you don't know who to talk
to. For example, suppose you need to look up a host name and get its Internet address.
Sometimes you don't know the address of the nearest name server. In that case, you might
send the r
equest as a broadcast. There are also cases where a number of systems are interested
in formation. It is then less expensive to send a single broadcast than to send datagrams
individually to each host that is interested in the information.


In ord
er to send a broadcast, you use an address that is made by using your network
address, with all ones in the part of the address where the host number goes. For example, if you
are on network 128.6.4, you would use 128.6.4.255 for broadcasts.
How this is actually
implemented depends upon the medium. It is not possible to send broadcasts on the
Arpanet, or on point to point lines. However it is possible on an Ethernet. If you use an Ethernet
address with all its bits on (all ones
), every machine on the Ethernet is supposed to look at that
datagram.



6
.4 Classless Inter
-
Domain Routing (CIDR)

CIDR, described in RFCs 1518 and 1519, removes the concept of class from the IP
address assignment and management
process. In place of predefined, well
-
known boundaries,
CIDR allocates addresses defined by a starting address and a range, which makes more efficient
use of available space. The range defines the network part of the address.

Notation method that specifi
es the number of masked bits in an IP address/subnet mask
combination. In this method bitmask is used to group of multiple classful networks as a single
network address. This will do the same process with route aggregation. supernetting is most
often appli
ed when the aggregated networks are under common administrative control. In class C
network addresses, supernetting can be used so that the addresses appear as a single large
network, or supernet.

For example an assignment from an ISP to a corporate client
might be expressed as
10.57.1.128 /25. This would result in a 128
-
address block for local use, with the upper 25 bits
being the network identifier part of the address. A legacy, class
-
full allocation would be
expressed as <net>.0.0.0 /8, <net>.<net>.0.0 /
16, or <net>.<net>.<net>.0 /24. As these are
reclaimed, they will be reallocated using classless CIDR techniques.


6.5

Multihoming

When a computer is configured with more than one IP address, it is referred to as a
multihomed system


6.6
Let us Sum Up

Classful Address

In classful addressing, the address space is divided into five classes: A, B, C, D, and E
to
define large, medium, and small networks.


Figure
6
.3a Classful address block size

Private IP addresses

Private IP addresses are a solution to the problem of the exhaustion of public IP
addresses.


Figure
6.
4a Private classful address and their ranges



Special Address


Network addresses 0 and 127 are reserved for
special uses.Network 0 designates the
default route.

0

is reserved for machines that don't know their address

255

is used for "broadcast".



Classless Inter
-
Domain Routing (CIDR)

CIDR allocates addresses defined by a
starting address and a range, which makes more
efficient use of available space.


For example an assignment from an ISP to a corporate client might be expressed
as 10.57.1.128 /25. This would result in a 128
-
address block for local use, with the upper 25
bits
being the network identifier part of the address


Multihoming

When a computer is configured with more than one IP address, it is referred to as a
multihomed system

6.7
Lesson end Activities

What are the different classification of classful address and their address range?


6.8
Points for Discussion


What is the purpose of having private IP address?


6.9
Check your progress


1.

What is Speical address?

2.

What is Classless Inter
-
Domain Routing
?


6.10 References


1.

“ Internetworking with TCP/IP Principles, Protocols, and Architecture Volume I”, Douglas
E. Comer, Prentice Hall of India Pvt. Ltd,

2.

“Computer Networks”, Andrew S. Tanenbaum, Prentice Hall of India Pvt. Ltd.

3.


Introduction to Data Communications and Networking”, Behrouz Forouzan, McGraq
-
Hill

4.

“MCSE Networking Essentials Study Guide”, Duncan Anderson, Tata McGraw
-
Hill


Lesson 7.
ARP & RARP

7.0 Aims and Objectives

7.
1 Introduction

7
.2 Address Resolution Protocol (ARP)

7
.3 Reverse Address Resolution Protocol (RARP)

7.4 Let us Sum Up

7.5
Lesson end Activities

7.6
Points for Discussion

7.7
Check your progress

7.8 References


7.0
Aim
s
and Objective
s


To learn Address and Reserve Address
Resolution Protocol

7
.1 Introduction

A data link such as Ethernet or a token ring has its own addressing scheme. When an
Ethernet frame is sent from one host to another, it is the 48
-
bit Ethernet address that determines
the destination. The first 28
-
bits a
re the organization that made the Ethernet card, the second 28
-
bits are randomly assigned by the manufacturer. The device driver software never looks at the
destination IP address in the IP datagram. Address resolution provides a mapping between two
differ
ent forms of addresses ie., 32
-
bit IP addresses and whatever the data link uses.

When an Ethernet frame is sent from one host on a LAN to another, it is the 48
-
bit
Ethernet address that determines for which interface the frame is destined. The device drive
r
software never looks at the destination IP address in the IP datagram.

7
.2 Address Resolution Protocol (ARP)

A Network layer protocol used to associate a logical address (IP) to a physical (hardware)
address (MAC). Obtains the hardware address (Ethernet
) of another computer on the same
network (subnet). This information is stored in a ARP table for future reference.


Figure
7
.1 ARP table in the system

ARP (address resolution protocol) is a protocol used to do address resolution in the TCP/IP
protocol suite (RFC826). ARP provides a dynamic mapping from an IP address to the
corresponding hardware address. ARP is required on multi
-
access channels and relie
s on the
ability to broadcast. The protocol broadcast a packet containing the IP address of the destination
machine. The machine with that address, or possibly a server, sends a reply containing the
hardware address.

This process is used by all
network devices
-
computers, routers, printers. Address resolution
provides a mapping between the two different forms of address ie., 32
-
bit Internet address and
48
-
bit Ethernet address. ARP provides a dynamic mapping from an IP address to the
correspondin
g hardware address. We use the term dynamic since it happens automatically and is
normally not a concern of either the application user or the system administrator.



Figure
7
.2 Sending a packet




Figure
7
.3 ARP table lookup

What happens if the device is unable to locate the destination MAC address in its ARP
table? In other words, the source knows the destination IP address, but is unable to locate a
MAC address for it in
its own ARP table.


Figure
7
.4 Unknown destination (Not in the table)

The device sends an ARP request packet to all devices on the subnet asking for the MAC
address corresponding to the IP address. The MAC address
in this request is in the form of a
broadcast: FF
-
FF
-
FF
-
FF
-
FF
-
FF. All devices will see the broadcast. The device with the
destination IP address will send a reply back to the requesting device. Once the sending device
has both of the destination’s IP and
Mac address in its ARP table, it can send data at any time. If
network devices did not keep an ARP table in memory (cache), they would have to send an ARP
request every time data needs to be transmitted. Obviously, very inefficient.

The ARP request message
contain the following details :

MAC header of



Destination:

FF
-
FF
-
FF
-
FF
-
FF
-
FF



Source :


02
-
60
-
8C
-
01
-
02
-
03

IP Header of



Destination:

197.15.22.126



Source :

197.15.22.33

ARP Request Message



“What is your MAC address?”



The ARP reply contain the following :

MAC header



Destination:

02
-
60
-
8C
-
01
-
02
-
03



Source :

08
-
00
-
02
-
89
-
90
-
80


IP header



Destination:

197.15.22.33



Source :

197.15.22.126

ARP request message



“Here’s my MAC address”

ARP Packet format

Format of ARP request or reply packet when used on an Ethernet.


Proxy ARP lets a
router answer ARP requests on one of its networks. This fools the sender of the ARP request
into thinking that the router is the destination host, when in fact the destination
host is "on the
other side" of the router. The router is acting as a proxy agent for the destination host,
relaying packets to it from other hosts.


Figure
7
.5 ARP packet format



Figure
7
.6. Encapsulation of ARP packet

Proxy ARP

Upon receipt the hardware address is used to send the original packet. Essential to the