Chapter 1 - Introduction to Internet

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Chapter 1Introduction to the Internet

Objective

To provide information on basic Internet terms and concepts

1.0 Introduction

The Internet is a network of computer networks. It makes it possible for any computer connected to it to send and receive

data from any other computer connected to it.

The Internet came as a result of crave for a robust, efficient, store and forward, data network

based on packets (packet switching) as against the circuit-switching (telephone network)

previously in existence. The Internet was developed by Paul Baran and Donald Davis in 1962. This packet switching

technology was first implemented in the US Defense Advanced Research Projects Agency (DARPA) as ARPANET, a largearea network developed by the Advanced Research projects Agency in late 60s. By early 70s ARPANET had spanned the

US continent and was extended to some parts of Europe by 1973 and later to the rest of the world.

By 1986, the US Science Foundation (NSF) initiated a network called NSFNET, which later

became a major component of the Net. Similarly, other networks were developed throughout the US through which the restof the world was connected to form a global network of systems and network called the Internet.

3.0 What is the Internet?

The Internet or simply the Net as it is often called, stands for interconnected network of networks on a global scale. It

makes it possible for computers all over the world to, send and receive messages. It is an internet-work of several hosts and

their networks together to form a larger network of global magnitude. It is therefore a global collection of computers and

networks that connects millions of peoples, organizations, military, and government to a wide range of information

resources through a common protocol to communicate among themselves.

Considering the global nature of the Internet, which involves several systems, running on different platforms, intersystem

communication becomes an issue. This problem is solved using the transmission control protocol/Internet protocol

(TCP/IP), which defines the rules for communication on the Net.

1.1 Internet: A Network of Information Networks

The Internet is a worldwide system of interconnected computer networks. The computers and computer networks exchangeinformation using TCP/IP (Transmission Control Protocol/Internet Protocol) to communicate with each other. TCP/IP is the

communication protocol for the internet. TCP/IP defines the rule computers must follow to communicate with each other

over the internet, ensuring that different networks (including hardware and software) communicate. Browsers and servers

use TCP/IP to connect to the Internet.

The Internet was initially developed to allow computers to share scientific and military information and was known as

ARPANET (Advanced Research Project Agency Network) in the late 1960s. The computers are connected via thetelecommunications networks, and the Internet can be used for e-mailing, transferring files and accessing information on

the World Wide Web.

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Figure 1.1 The Internet: Computer Network Hierarchy

When you connect to the Internet, your computer, Personal Digital Assistant (PDA) or mobile device becomes part of a

network. Every computer that is connected to the Internet is part of a network. For example, you may use a modem and diala local number to connect to an Internet Service Provider (ISP). At work, you may be part of a local area network(LAN),

but you most likely still connect to the Internet using an ISP that your company has contracted with. When you connect to

your ISP, you become part of their network. The ISP may then connect to a larger network and become part of their

network. The Internet is simply a network of networks.

Most large communications companies have their own dedicated backbones connecting various regions. In each region, the

company has a Point of Presence (POP). The POP is a place for local users to access the company's network, often througha local phone number or dedicated line. The amazing thing here is that there is no overall controlling network. Instead,

there are several high-level networks connecting to each other through Network Access Points or NAPs.

America Online, Comcast, Earthlink, etc. are examples of Internet service providers. They make it physically possible foryou to send and access data from the Internet. They allow you to send and receive data to and from their computers or

routers which are connected to the Internet.

Some Internet timeline:

1976 - UUCP (Unix-to-Unix CoPy) developed at AT&T Bell Labs.

1978 - TCP/IP

1979 - USENET started

1984 - DNS introduced

1988, Nov 2 - Internet Worm affects about 6,000 of the 60,000 hosts on the Internet

1990, November - Proposal for a HyperText Project (CERN).

1991 - WYSIWYG available on the Internet, first Web server in USA (Stanford Linear Accelerator Center in

California)

1992 - The world has 50 Web servers!

1993, February - First X Web browser, NCSA Mosaic. About 200 Web servers.

1994, March - Marc Anderessen and his group leave NSCA to form Netscape with Jim Clark. About 2500 Web

servers exists.

1995, May 23 - Sun Microsystems launches Java. First search engines. Approximately 73500 servers.

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1996 - WWW browser war between Netscape and Microsoft started. By the endo of the year about 603K Web

sites exists.

1998 - In the first quoter Web size estimates more than 300 million pages. E-Commerce, E-Auctions, Portals. By

the end about 3.5M Web sites.

1999 - By the end of 1999 there are about 10 million Web sites.

It seems like everyone's talking about the Internet these days. But what is it really? How does it work? How doyou access it? And most important, what can it do for you at work or at home?

Fortunately, accessing and using the Internet is fairly simple. Let this tutorial be your guide to the Internet as you

connect for the first time and explore the network's vast and useful resources.

How Does the Internet Work?

The Internet is a worldwide collection of computer networks, cooperating with each other to exchange data using a

common software standard. Through telephone wires and satellite links, Internet users can share information in a

variety of forms. The size, scope and design of the Internet allows users to:

connect easily through ordinary personal computers and local phone numbers;

exchange electronic mail (E-mail) with friends and colleagues with accounts on the Internet;

post information for others to access, and update it frequently;

access multimedia information that includes sound, photographic images and even video; and

access diverse perspectives from around the world.

An additional attribute of the Internet is that it lacks a central authorityin other words, there is no "Internet, Inc."

that controls the Internet. Beyond the various governing boards that work to establish policies and standards, the

Internet is bound by few rules and answers to no single organization.

The History of the Internet

Many people think that the Internet is a recent innovation, when in fact the essence of it has been around for over a

quarter century. The Internet began as ARPAnet, a U.S. Department of Defense project to create a nationwide

computer network that would continue to function even if a large portion of it were destroyed in a nuclear war or

natural disaster.

During the next two decades, the network that evolved was used primarily by academic institutions, scientists and

the government for research and communications. The appeal of the Internet to these bodies was obvious, as it

allowed disparate institutions to connect to each others' computing systems and databases, as well as share data via

E-mail.

The nature of the Internet changed abruptly in 1992, when the U.S. government began pulling out of networkmanagement, and commercial entities offered Internet access to the general public for the first time. This change in

focus marked the beginning of the Internet's astonishing expansion.

According to a survey conducted by CommerceNet and Nielsen Media Research in early 1997, nearly one out of

every four Americans over the age of 16 is an Internet user. And the number of users worldwide is believed to be

well into the tens of millions. Other statistics are equally startling:

A CNN report stated that Internet traffic in 1996 was 25 times what it was just two years earlier.

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The market research group IntelliQuest pegged the number of Internet users in the U.S. in late

1996 at 47 million - a 34 percent increase over the first quarter of that year.

According to IBM, 146 countries currently have at least some level of Internet access.

The technology research firm IDG estimates that by century's end, one billion people worldwide

will have access to personal computersmore than doubling the computer-savvy population of 1996.

The Internet explosion coincides with the advent of increasingly powerful yet reasonably priced personal

computers with easy-to-use graphical operating systems. The result has been an attraction of recent computer"converts" to the network, and new possibilities for exploiting a wealth of multimedia capabilities.

What Kinds of Information are Available?

In addition to text documents, the Internet makes available graphics files (digitized photographs and artwork), and

even files that contain digitized sound and video. Through the Internet, you can download software, participate in

interactive forums where users post and respond to public messages, and even join "chats," in which you and other

users type (and, in some cases, speak) messages that are received by the chat participants instantly.

How Do People Use the Internet?

Obviously, the Internet can bring you a whole host of capabilities. But how can they be put to practical use?

Among the ways that users like yourself are taking advantage of the Internet are:

Sharing research and business data among colleagues and like-minded individuals.

Communicating with others and transmitting files via E-mail.

Requesting and providing assistance with problems and questions.

Marketing and publicizing products and services.

Gathering valuable feedback and suggestions from customers and business partners.

The Internet's potential is limited only by users' vision and creativity. And as the Internet grows, new and

innovative uses will surely follow.

The Sum of Many Parts: Internet Components

The Internet components most Internet users are familiar with are e-mail, the web, andweb access. Unlike many computer networks, the Internet consists of not one but multiple data systems thatwere developed independently. The most popular and important systems are:

E-mail, for exchange of electronic mail messages.

USENET newsgroups, for posting and responding to public "bulletin board" messages.

File Transfer Protocol (FTP), a system for storing and retrieving data files on large computer

systems.

Gopher, a method of searching for various text-based Internet resources (largely obsolete).

TELNET, a way of connecting directly to computer systems on the Internet.

Internet Relay Chat (IRC), a system for sending public and private messages to other users in

"real time"that is, your message appears on the recipient's screen as soon as you type it.

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CU-SeeMe, a videoconferencing system that allows users to send and receive sound and pictures

simultaneously over the Internet.

World Wide Web - This is largest, fastest growing, and most exciting partof the Internet today. Business is the leading factor fueling the rapid growth of the

Web making information, advertising, and product ordering readily available toeveryone with Web access. We will learn more about the World Wide Weband how you can

benefit from itin thenext chapter.

The Internet Concept

Internet can be termed as the interconnection of the variety of networks and computers. Internet makes use of theinternet protocol and the transmission Control protocol. Internet opened the doors of communication between thevarious stations. Internet facilitates storing and transmission of large volumes of data. The internet is one of themost powerful communication tools today.

In the 1990s internet gained popularity in the masses. People started becoming aware of the uses of internet.Internet helped the people to organize their information and files in a systematic order. Various researches wereconducted on internet. Gopher was the first frequently used hypertext interface.

In 1991, a network based implementation with respect to the hypertext was made. The technology was inspired bymany people. With the advent of the World Wide Web search engine the popularity of internet grew on anextensive scale. Today, the usage of internet is seen in science, commerce and nearly all the fields

There are various ways and means to access the internet. With the advancement in technology people can nowaccess internet services through their cell phones, play stations and various gadgets. There are large numbers ofinternet service providers as well.

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With the development and the wide spread application of internet electronic mail people from all across the globecome together and communication has become much easier than ever before. Messages, in the form of Emailscould be send in at any corner of the world within fractions of seconds. Emails also facilitated masscommunication (one sender many receivers).

Emails, video conferencing, live telecast, music, news, e-commerce are some of the services made available dueto internet. Entertainment has taken new dimensions with the increase of internet and all we see it's a continous

development and transformation.

Connection Options

Until recently, the two primary methods of accessing the Internet were through a network connection, allowing

users of local area networks (LANs) to go online through their school or workplace systems, and dial-up

connections through a modem and phone line. However, new connection options allow for greater speeds and

flexibility, while keeping costs to a minimum.

The following are some of the newer connection options that you might want to investigate:

Cable InternetThese systems allow your computer to connect to the Internet through the

same cable that carries your TV signal. Monthly service charges are usually not much more than standardmodem connection costs, but you have to rent or purchase a "cable modem." Additionally, your computer

will need an Ethernet card (a special circuit board that allows for network connections). Not all cable

service operators offer this service; call your local operator for more information.

Satellite connectionsDirecPC (http://www.direcpc.com/ ) allows you to download Internet

files via a satellite connection. This is an efficient method for receiving large Web graphics and other

items, but you still need a modem connection for other features. You must purchase the connection

hardware as well as subscribe to the service.

Integrated Services Digital Network (ISDN)An ISDN line is a type of digital phone line thatcan transmit data many times faster than a conventional modem and phone line. To learn more about

ISDN, go to http://www.isdn.ocn.com/index.shtml

Wireless connectionsPagers, cellular phones and personal digital assistants (PDAs) now

allow varying levels of Internet access, from notification of E-mail to limited Web connections. Many of

these services remain in the experimental stage. WebTVIntroduced in late 1996, WebTV (http://www.webtv.net/) provides Web and E-mail

access through ordinary television sets. The connection is made through a custom high-speed modem.

You must purchase a special set-top unit for your TV, plus subscribe to the connection service. Recently,

similar systems by other manufacturers have appeared on the market to compete with WebTV.

The Domain Name System

Introduction

A key component of the Internet and how it works revolves around the Domain Name System,otherwise known as DNS. The underlying technology behind the Internet, is that when a

computer needs to talk to another computer on the Internet, they communicate via thecomputer's IP Address. The IP Address is a unique set of numbers associated with a particular

machine. An example of an IP Address is 216.213.19.27, which is the IP Address thatcorresponds to www.bleepingcomputer.com.

As the predecessor of the Internet, ARPANET, grew larger, connecting to remote machines bytheir IP Address grew cumbersome. It became more and more difficult for people to remember

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the IP Addresses associated with the machines they were trying to reach that a system wascreated to translate easier to remember symbolic names to their equivalent numerical IP Address.

Thus the Domain Name System was born.

Domain Name System

The Domain Name System is the system used on the Internet for the mapping of names, such as

www.google.com, to IP Addresses such as 216.239.51.99. Every time a new domain, likebleepingcomputer.com, is registered, that domain is entered into one of the 13 Root Serversspread throughout the world and overseen by an organization called ICANN. Because your domain

is in one of these servers, it can be reached and understood by the rest of the users on theInternet.

Another key element of the Domain Name System are DNS Servers run by Companies andInternet Service Providers. Every time you connect to a site, you are asking your ISP's DNS

Server to resolve, or convert, the hostname such as www.google.com to a an ip address such as216.239.51.99. If your ISP's name server is not working or can not be reached, then you will not

be able to traverse the Internet using hostnames, but instead would have to use their IP Addressequivalent.

Any time you connect to a site, your ISP DNS Server must find out what name server has theinformation about the domain for the site you are trying to reach. Your ISP's DNS Server will

connect to a Root Server and ask it who the name server is that knows the information about thesite you are trying to reach. The Root Server will tell your ISP's DNS Server what server they

should next contact for information. Next your ISP's DNS Server will then contact the server that

the Root Server told it to contact, where it will be given the IP Address associated with the siteyou are trying to reach.

Real Life Example

A lot of what has been discussed may be a bit confusing, so lets do a real life example. In theflowchart below labeled Figure 1, you will see a computer trying to connect to www.google.com

and the steps it takes.

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We will discuss these steps below:

1. A User opens a web browser and tries to connect to www.google.com. The operating

system not knowing the IP Address for www.google.com, asks the ISP's DNS Server forthis information.

2. The ISP's DNS Server does not know this information, so it connects to a Root Server tofind out what name server, running somewhere in the world, know the information about

google.com.3. The Root Server tells the ISP's DNS Server to contact a particular name server that knows

the information about google.com.4. The ISP's DNS Server connects to Google's DNS server and asks for the IP Address for

www.google.com.5. Google's DNS Server responds to the ISP's DNS server with the appropriate IP Address.

6. The ISP's DNS Server tells the User's operating system the IP Address for google.com.7. The operating system tells the Web Browser the IP Address for www.google.com.

8. The web browser connects and starts communication with www.google.com.

Domain Names and HostNames

All the entities and inter-mediaries of the Net are given unique names for easy identification and delivery of messages.

Thus, all the hosts/nodes on the Internet are identified through a unique identifier called domain names. The domain

name doesn't include the server name

NOTE: Hosts are the organization who owns a particular network while nodes are the

various computers connected the Internet via the host.

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The major parties involved in information dissemination are the users (people) and the systems (IT equipment). Therefore,

domain names must be convenient and informative for all the parties to operate effectively. Users prefer the alphabetic

naming conventions to recognize the hosts, while the computers or systems use the IP addresses.

Generally, domain names are composed of 3 or 4 parts namely: Hostname, Organization, Subdomains (optional) and

Country name.

e.g:Hostname.Organizationname.Type of categorization.Countryname

ORHostname.Domain.Top-level domain.International top-level domain.

Where the top-level domains include:

.com for commercial

.mil for military

.edu for education

.org for organization

.net for information services/network

etc.

and the international top-level domain use a 2-letter country code such as:

.ng for Nigeria

.us for United States

.uk for United Kingdometc.

When you use the Internet, you use domain name and hostnames all the time. These hostnamesand domain names when put together become the Internet address that you search with. The

domain name without a hostname is also the most common email address. This article willexplore what hostnames and domain names are and how they are used. We will also discuss

TLD's, or Top Level Domains, such as .Com, .Net, .Org, etc.

Non Geographic Top level Domain Names

Non Geographic Top level Domain Names and uses.com This is the most popular TLD. It is used mainly for

US commercial organizations. It is the most populardomain name extension on the Internet. Anyone

can have a .com, but it is more difficult to think upa unique name that hasn't already been registered.

Because of this many domain name registrars offeralternative names when checking and registering a

domain name.

.net This is the second most popular TLD. It generally

describes the entity owning the domain name as anetwork and is used mainly by organizations that

provide network connection services.

.org In general, non-profit organizations tend to use thisextension.

.gov Generally used for government agencies. Restricted

.int Intended to be used for sites relating toInternational Treaties or containing international

databases. For this reason, it is not widely used.Restricted

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.mil Mainly used by military organizations of the US

government. Restricted

.name This is a new TLD extension and is intended to allowindividuals to register their names (i.e. first name.

Last name .name) as a personal domain name on

the Internet.

.biz This is a new TLD extension for businesses; .biz is

intended to be an alternative to the .com.

.info This is also new TLD, and is freely available to

anyone with a business, government or non-commercial site.

.aero This is a new restricted TLD for service companies

dealing with air travel.

.pro This is a new restricted TLD for professions such

as law, medicine, and accounting.

.coop - This is a new restricted TLD for cooperative

organisations

.museum This is a new restricted TLD for museums, archivalinstitutions and exhibitions.

Domain Names

Domain Names are the unique name that identifies an entity, whether that be an single individualor a company, on the Internet. Domain Names always have 2 or more parts seperated by the

dots. The leftmost piece is the most specific part while the right part is the TLD or Top LevelDomain.. Lets disect a domain name so you can see what were are talking about.

Take the domain name bleepingcomputer.com. This domain name consists of two parts. Theleftmost part is the word that identifies the entity, in this situation its bleepingcomputer. This is

a unique name and there can not be any duplicates on the rest of the Internet that are used byanyone else. The second part, or the rightmost part is the TLD, or Top Level Domain. This is .Com

which means that it is a commercial organization.

In the beginning there were only 5 Global TLD's that were recognized by everyone. These TLD'sare discussed below:

.com

This TLD is intended for Commercial business around the world..net

This TLD is historically and is still used by Internet Service Providers..org

This TLD is intended to search the noncommercial community..mil

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This TLD is restricted to use by the United States Military..gov

This TLD is restricted to use by United States Government Agencies.

As the Internet grew and expanded throughout the world, new TLD's were created to represent

different countries. For example the TLD .uk is for the United Kingdom and .au is for Australia. Asmore and more domains were registered, available domain names in the above TLD's were hard

to come by. Due to this more TLD's such as .biz, .info, .name were created to allow more peopleto register domain names that fit their needs.

Hostnames

Hostnames can be a confusing as they have a double meaning. The hostname of an Internet

Address is all of the left most pieces of a full internet address if there are more than 2 parts to theaddress. If there are only 2 parts of the address, then the hostname is equivalent to the domain

name.

Here are some examples:

Full Address Hostname Domain Name TLD

www.bleepingcomputer.com www bleepingcomputer.com com

bleepingcomputer.com bleepingcomputer.com bleepingcomputer.com com

www.google.net www google.net net

my.www.bleepingcomputer.com my.www bleepingcomputer.com com

As you can see from the examples the hostname can be many different things.

If the entire address consists of only 2 parts, then the hostname is equivalent to the

domain name.

If the entire address consists of more than 2 parts, then the hostname is equivalent to allthe left most pieces before the right 2 parts (or the domain name)

To make things even more confusing, you can refer to the full address in its entirety as ahostname. For example, with www.bleepingcomputer.com:

Bleepingcomputer.com is the domain name.

www is the hostname

www.bleepingcomputer.com is the hostname as well!!!

Each system on a network or Internet is assigned a unique IP address by which it is identified. Furthermore, for easy

identification and operations of the entire system, the domain name service (DNS), maintains a database of computer names

and IP addresses corresponding to each of them. That is, the DNS is responsible for translating domain names to IP

addresses and vice versa as occasions demand between the users and the systems.

For proper organization and assignment of domain names and IP addresses, the Internet

Corporation for Assigned Names and Numbers (ICANN), is saddled with the responsibility of managing and assigningnames and IP addresses. ICANN is a special organization with a charter from the US government to oversee the registration

of names on the Internet alongside some domain name Registrars such as www.netsol.com and www.registrar.com to

manage the process.

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IP addresses

introduction

Every machine on the the Internet has a unique number assigned to it, called an IP address.

Without a unique IP address on your machine, you will not be able to communicate with other

devices, users, and computers on the Internet. You can look at your IP address as if it were atelephone number, each one being unique and used to identify a way to reach you and only you.

IPv4 and IPv6 Addresses

There are two flavors ofIP Addresses that can be used on a network. The first, and the version

that the Internet and most routers are currently configured for, is IPv4 or Internet Protocolversion 4. This version uses 32-bit addresses, which limits the amount of addresses to

4,294,967,296 possible unique addresses. Some of these addresses, about 290 million, are also

reserved for special purposes. Due to the popular growth of the Internet there has been concernthat the pool of possible addresses would be exhausted in the near future. With this in mind, a

new version of IP addresses was developed called IPv6, or Internet Protocol version 6, that would

change the address size from 32-bit address to 128-bit addresses. This change would allow forgenerous IP address allocations to networks without any foreseeable problem with the amount ofaddresses available. In order to use IPv6 addresses, though, existing routers and hardware would

need to be upgraded or configured to use this new version of IP addresses.

As IPv4 is still the most commonly used, we will be focusing on that version of IP addresses.

The Address Itself

An IP address always consists of 4 numbers separated by periods, with the numbers having a

possible range of 0 through 255. An example of how an IP address appears is: 192.168.1.10

This representation of an IP address is called decimal notation and is what is generally used byhumans to refer to an IP address for readability purposes. With the ranges for each number beingbetween 0 and 255 there are a total 4,294,967,296 possible IP addresses.

Out of these addresses there are 3 special ranged that are reserved for special purposes. The firstis the 0.0.0.0 address and refers to the default network and the 255.255.255.255 address which

is called the broadcast address. These addresses are used for routing, which will not be coveredin this tutorial. The third address, 127.0.0.1, is the loopback address, and refers to your machine.

Whenever you see, 127.0.0.1, you are actually referring to your own machine. That means if youclicked on this link, http://127.0.0.1, you are actually trying to connect to your own computer,

and unless you have a web server running, you will get a connection error.

There are some guidelines to to how IP address can appear, though. The four numbers must bebetween 0 and 255, and the IP address of 0.0.0.0 and 255.255.255.255 are reserved, and are

not considered usable IP addresses. IP addresses must be unique for each computer connected toa network. That means that if you have two computers on your network, each must have a

different IP address to be able to communicate with each other. If by accident the same IPaddress is assigned to two computers, then those computers would have what is called an "IP

Conflict" and not be able to communicate with each other.

IP addresses are unique four octect numbers expressed either as binary dotted or decimal dotted.

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e.g:

To convert IP address from binary to decimal form, we convert each of the four 8-bits numbers in each octets according to

the table below:

IP address classes

These IP addresses can further be broken down into classes. There are five different classes of addressdesigned to meet the needs of different organizations. The various classes are given as A, B, C, D and E. The classes are

distinguished from each other by the decimal notation of the first octet. The class range is presented in the table below:

Class Start address Finish address

A 0.0.0.0 126.255.255.255

B 128.0.0.0 191.255.255.255

C 192.0.0.0 223.255.255.255

D 224.0.0.0 239.255.255.255

E 240.0.0.0 255.255.255.255

Figure 2. IP address Classes

If you look at the table you may notice something strange. The range of IP address from Class Ato Class B skips the 127.0.0.0-127.255.255.255 range. That is because this range is reserved for

the special addresses called Loopback addresses that have already been discussed above.

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127 is reserved for loopback (127.0.0.1) for internal testing on the local machine. Web

applications can be tested on the local machines using the loopback (localhost) before deployment to the web.

The rest of classes are allocated to companies and organizations based upon the amount of IP

addresses that they may need. Listed below are descriptions of the IP classes and the

organizations that will typically receive that type of allocation.

Default Network: The special network 0.0.0.0 is generally used for routing.

Class A: From the table above you see that there are 126 class A networks. These networks

consist of 16,777,214 possible IP addresses that can be assigned to devices and computers. Thistype of allocation is generally given to very large networks such as multi-national companies.

Loopback: This is the special 127.0.0.0 network that is reserved as a loopback to your own

computer. These addresses are used for testing and debugging of your programs or hardware.

Class B: This class consists of 16,384 individual networks, each allocation consisting of 65,534

possible IP addresses. These blocks are generally allocated to Internet Service Providers andlarge networks, like a college or major hospital.

Class C: There is a total of 2,097,152 Class C networks available, with each network consisting of

255 individual IP addresses. This type of class is generally given to small to mid-sized companies.

Class D: The IP addresses in this class are reserved for a service called Multicast.

Class E: The IP addresses in this class are reserved for experimental use.

Broadcast: This is the special network of 255.255.255.255, and is used for broadcasting

messages to the entire network that your computer resides on.

Private Addresses

There are also blocks of IP addresses that are set aside for internal private use for computers notdirectly connected to the Internet. These IP addresses are not supposed to be routed through the

Internet, and most service providers will block the attempt to do so. These IP addresses are usedfor internal use by company or home networks that need to use TCP/IP but do not want to be

directly visible on the Internet. These IP ranges are:

Class Private Start Address Private End Address

A 10.0.0.0 10.255.255.255

B 172.16.0.0 172.31.255.255C 192.168.0.0 192.168.255.255

If you are on a home/office private network and want to use TCP/IP, you should assign your

computers/devices IP addresses from one of these three ranges. That way your router/firewallwould be the only device with a true IP address which makes your network more secure.

Common Problems and Resolutions

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The most common problem people have is by accident assigning an IP address to a device onyour network that is already assigned to another device. When this happens, the other computers

will not know which device should get the information, and you can experience erratic behavior.On most operating systems and devices, if there are two devices on the local network that have

the same IP address, it will generally give you a "IP Conflict" warning. If you see this warning,that means that the device giving the warning, detected another device on the network using the

same address.

The best solution to avoid a problem like this is to use a service called DHCP that almost all homerouters provide. DHCP, or Dynamic Host Configuration Protocol, is a service that assigns

addresses to devices and computers. You tell the DHCP server what range of IP addresses you

would like it to assign, and then the DHCP server takes the responsibility of assigning those IPaddresses to the various devices and keeping track so those IP addresses are assigned only once.

3.3 Information Routing on the Internet

Data passage within an internet-work is via a router. That is, with the unique IP addresses

assigned each of the systems, a packet of data is transmitted from one node to another through the router. Among the

various network interconnecting devices such as bridge, switch, hub, repeater, gateway and router, the routers is the most

ideal because of its capability to handle complex situations like the Internet, although it is the most expensive of them. The

router maintains a routing table, which contains the IP address of all the adjacent nodes, the various subnets of the Internet.Similarly, it has the capability of routing packets of data through the shortest route using a number of routing algorithms.

These make it a preferred candidate for a complex network of great magnitude like the Internet.

3.3.1 The Internet Model

This model predates the open standard interconnection (OSI) model. It dates back to the

ARPANET (the origin of the Internet) and hence, often referred to as the department of defense (DoD) model. The OSI

model is composed of a seven-layered architecture along which network communications are segmented. Each layer covers

a specific type of network activities, equipment or protocols. The layers are: Application, Presentation, Session, Transport,

Network, Data Link, and Physical. The DoD model is a four-layered architecture that does not map the OSI layer perfectlybut can be relayed as follows:

____________*************

The OSI Model is one way of describing how networks work, but it's not the only way. When you describe the way the

Internet works, you don't always see all seven layers of theOSI Modelas separate layers. The OSI Modelis a seven layer

design model and theInternetonly needs a four layer model to describe how it works. If you haven't already read the OSI

Model tutorial, you should go back and look at it now.

The Internet only utilizes a few of the OSI Model's seven layers. Functionality of other layers is combined in some cases or

not used at all. For example, the network interface device is said to compose the Physical and Data Link layers of the OSI

Model, while a web browser performs the functions of the OSI Model's Session, Presentation and Application layers.

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Telnet likewise handles Session, Presentation and Application issues. A web browser or a telnet session utilize IP addresses

to reach the computerthey are communicating with. Every device that communicate with a local network will use a MAC

address that is unique on that LAN (but only if the computing device is using an 802.x protocol). IP addresses are mapped

to specific MAC addresses on a local LAN.

At each layer, information unique to that layer is used to identify the specific computerand specific service that is beingcommunicated with.

OSI Model (7 layers) Internet Model

Layer Name Layer Name Protocol Address

Application

Application

Telnet hostname

Presentation E-mail User@domain

Session Web Browser URL

Transport Transport

Transmission Control Protocol

orUser Datagram Protocol

Port Numbers

Network Network Interrnet Protocol IP Address

Data Link Data Link Network

Interface

Device

MAC AddressPhysical Physical

__________________**********************

Layer 4: Process/Application Layer

This layer combines the functionality of the topmost three layers of the OSI model. That is,

application, presentation and session. The protocols include: e-mail, telnet, network management and directory services

(NFS).

Layer 3: Host-to-Host LayerThis layer is the equivalent of the transport layer of the OSI model. It is responsible for end-to-end data integrity. The two

protocols here are transmission control protocol (TCP) and the user datagram protocol (UDP). TCP offers reliable servicesand full duplex connections, while the UDP provides unreliable services that enhance throughput when error connection is

not involved.

Layer 2: Internet Layer

This Layer corresponds to the network layer of the OSI model. Thus, it is responsible for routing packets within the

internetwork. Gateways and routers are used for that purpose.

The TCP/IP protocol at this layer is the Internet protocol (IP) which operates a system of logical host addresses called IP

addresses.

Layer 1: Network Access Layer

This combines the functionalities of both the physical and data link layers of the OSI model. It is responsible for exchange

of data between a host and the network as well as delivery of data between two devices on the same network.

Communication between two systems through DoD model is as illustrated in figure 1.3 below:

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Communication between two systems over the Internet is described as follows:

The packet of data is sent down the four layers of the DoD model from Application, throughTCP, IP to Hardware (network cable, NIC) from where it is sent to the Internet and delivered to the destination system via

the hardware (network cable, NIC), through IP, TCP and Application. However, as the packet travels from one layer to

another it wrapped into an envelope with the necessary information to the next layer. When received, it is unwrapped and

rewrapped for the next lower layer. The procedure is repeated down the layers of the sending system and up the layers of

the receiving system until it gets to the specified IP address. The process of wrapping and unwrapping packets of data is

also known as encapsulation and decapsulation respectively.

3.4 Application Layer Protocols

1. HTTP This is known as hypertext transfer protocol. It is a connectionless text-based

protocol through which clients (web browsers) send requests to the web server for certain web pages and images to be

displayed. After servicing this request, the connection between the client and the server across the Net is disconnect.

However, for another request from the client to be serviced, another connection is sought.

2. Telnet This is an application layer protocol that enables users to execute terminal

sessions with remote hosts. That is, it allows a user to login to another host at remote location.

3. FTP This stands for file transfer protocol. It enables transfer of files between two hosts

that are at remote locations to each other. It performs basic file transfer between hosts.

4. SMTP This stands for simple mail transfer protocol. This is a protocol that is used forexchanging electronic mail. It is used for basic message delivery.

5. SNMP This is known as simple network management protocol. It is a protocol that is

used to manage the network. It is used to collect information from the connected devices on the network for management

purposes.

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