Introduction – Computer Network Part 1

Jayaseelan Vejayon

Internet

• Interconnection of networks worldwide

• Allows communication and sharing of information between connected systems

• Uses Internet Protocol

• Popular applications– World Wide Web– E-mail– File transfer & sharing– Voice and video streaming

Any difference between ‘Internet’ and ‘internet’?

• YES!

• internet is interconnection of networks

• Internet with capital 'I' refers to the internet as in the world wide web

• Confused? Read again!

What is needed to visit a website in the Internet?

• A machine installed with TCP/IP protocol• Gateway / Router / Proxy server• DNS server• A browser program• The URL / IP address of the website

TCP/IP

• TCP and IP are communication protocols for the Internet

• Try this– Check the network properties of your machine

to find out whether your machine has TCP/IP installed. Write the IP address of your machine. You can use ‘ipconfig’ command to find your machine’s IP address.

– Use the ‘ping’ command to check whether you have connectivity with your friends’ machines.

– Type ‘ping/?’ in the command prompt to view the options of this command. If you want to continuously ping, what option will you use?

Internet Protocol• Every computer that communicates on a

network needs its own IP address • Static and Dynamic

– Static addresses are permanently configured for a machine

– Dynamic addresses are given by DHCP servers– Question: When you are connected to Internet

through your home Streamyx, what type of IP are you getting: static or dynamic? Why?

• Public and private– Public IPs can be seen on the Internet– Private IPs can only be used within a

broadcast domain• ranges associated with addresses 10.0.0.0,

172.168.0.0, and 192.168.0.0 through 192.168.255.0.

• Question: what type of IP is your machine’s? Private or public? Is it static or dynamic?

IPv4 and IPv6• Two standards of IP addresses being used

today• IPv4

– has 4 billion addresses but they are not enough for the growing number of machines connected to the Internet

• IPv6– has 2128 addresses=3.4x1038 addresses– ISPs are moving into implementing IPv6

addresses because of its many advantageous features

• Fact finding: Find the role of National Advanced IPv6 Center in the implementation of IPv6 technology in Malaysia. Why need a National organisation to implement IPv6 addresses? Visit http://www.nav6.org to find your answers. (15 minutes)

Domain name

• The name of a computer on the Internet• The domain name service (DNS) converts

domain names to IP addresses• Who runs the DNS?

– Millions and millions of servers– DNS database is the biggest database in the

world• Some Top Level Domains - .com, .org, .net• nslookup is a command that you can use to

check whether a domain name and its IP are available in a DNS server

• Try this– Find whether the domain name nav6.org

is available in OpenDNS and 202.188.0.133 servers

– How to do this?• Search the OpenDNS IP from the Internet

and use command nslookup – OpenDNS-IP nav6.org

• Now try the same command again with DNS IP 202.188.0.133

• See the results. Is the name found in the DNS servers?

URL

• Uniform Resource Locator– the global address of documents and other resources on

the World Wide Web– The first part of the address is called a protocol

identifier and it indicates what protocol to use– The second part is called a resource name and it specifies

the IP address or the domain name where the resource is located

– For example, the two URLs below point to two different files at the domain nav6.org. The first specifies an executable file that should be fetched using the FTP protocol; the second specifies a Web page that should be fetched using the HTTP protocol:» ftp://www.nav6.org/sample.exe» http://www.nav6.org/v3/index.html

Internet Browser

• A program used to view web pages• Question: Can you name some

popular internet browsers?

A web page•Is created using HTML tags.

Try this: Open Notepad and type the tags and statements below. Save it with extension .htm or .html. Then open it with an Internet browser.

<html><head></head><title>This is my title</title><body><H1>Hello world</H1><H2>Hello world</H2><H3>Hello world</H3></body></html>

Creating a web page using Microsoft Word

• You can create a web page easily using Microsoft Word.

• You can create a page by just creating a document and saving it as a web page.

• If you have never tried it, try it!

Protecting your PC

• What should you do?– Install antivirus – Try this by downloading a

free antivirus like AVG or Avira antivirus and installing them in your PC

– Enable your PC firewall – Try this– Update your operating system regularly – Try

this by using Windows Update– Install a reliable anti-spyware – Try this by

installing Windows Defender. You can also download and install Search & Destroy Spybot

• What else should you do?– Don’t accept applications from the websites if

you not sure of their contents– Don’t open attachments from your emails if

they look suspicious

THANK YOU

JAYASEELAN VEJAYON