CHAPTER 2

PCs on the Internet

Suraya Alias

The TCP/IP Suite of Protocols

Internet applications – client/server applications The client requested data from the server Example : a home user (client) requesting the facebook web

page from facebook application web server (web host) Example of web servers : Apache HHTP Server and Internet

Information Services (IIS) The server application is installed as a service in a computer

Using IP and Ports addresses to identify services Each services (email, web server) is addressed using unique port

number since they access to the same IP Address So each server applications listens to the assigned port Example: web server is assigned port 80, email server is port 25 So the web server will communicate at 136.60.30.5:80 and the email

server using 136.60.30.5:25

Common TCP/IP port assignmentPort Protocol Service Description

20 FTP FTP File transfer data

21 FTP FTP File transfer data

22 SSH Secure Shell Remote control to a networked computer

23 Telnet Telnet Used by UNIX computers to control a computer remotely

25 SMTP E-mail Simple Mail Transfer Protocol

80 HTTP Web server World Wide Web Protocol

109 POP2 E-mail Post Office Protocol,v2, used by client to receive email

110 POP3 E-mail Post Office Protocol,v3, used by client to receive email

119 NNTP News server New server, used for newsgroup

143 IMAP E-mail Internet Message Access Protocol, newer than POP3

443 HTTPS Web server HTTP with security includes authentication and encryption

TCP/IP protocol layers

Web server Email Chat room FTP

Applications

HTTP SMTP, POP

IRC FTP

TCP Or UDP

IP, ARP,RARP,RIP or ICMP

Ethernet, PPP over telephone lines, Token Ring, FDDI or wireless

Cabling/telephone lines

TC

P/I

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Applications

Operating System

Physical Network

Application Protocols

Four common applications that uses the internet is Web browser, email, chat and FTP

Application Programming Interface (API) is used by the OS in order to request or send data to another host

For web browser and web servers, the OS generates Hypertext Transfer Protocol (HTTP) in order to communicate

A session is established after the response is received from the web server

TCP/IP protocols used by OS for network communication

When a web browser make a request for a data to the web server, a packet is created and is ready to be delivered

Transmission Control Protocol (TCP) is the TCP/IP protocol that guarantees the packet is delivered and will resend if it fails

It is also called connection-oriented protocol and used for email and web browsers, s

While UDP (User Datagram Protocol) does not guarantee delivery by first connecting and checking whether data is received or not

Its called a connectionless protocol or best-effort protocol

TCP/IP protocols used by OS for network communication Next, TCP & UDP pass the request to IP (Internet

Protocol) to breaks up and reassemble data into packets and routing them to respective destination

Other available network protocols; ARP (Address resolution Protocol)

Responsible to locate a host on a local network RARP (Reverse Address resolution Protocol)

Responsible for discovering the Internet Address of a host on a local network

ICMP (Internet Control Message Protocol) Responsible for communicating problem with transmission

Example of TCP/IP utilities ARP, Getmac, IPconfig,FTP,NBstat,Netstat, NSLookup Ping, route, telnet, tracert, winipcfg

TCP/IP Utilities

Connecting to the Internet

Computer or Local network can connect to Internet by ISP using following technologies;

1. Regular phone line - requires internal, external modem

2. Cable modem - uses cable lines3. DSL (Digital Subscriber Line) – uses copper phone

lines, same phone line for voice and DSL, Asymmetric SDL,Symmetric DSL

4. ISDN (Integrated Services Digital Network)5. Satellite access6. Wireless access

Using Router Router is a device that manages traffic between

two network 2 major disadvantages of using host pc in sharing

internet connection1. Host comp must always be turned on2. Security issues

Advantages of using router rather than host pc1. Less bottleneck of the host pc2. Internet access not dependable to host pc3. Router can serve as hardware firewall, better protection

that software firewall4. Provide additional features such as DHCP server, switch,

wireless access point.

Virtual Private Network (VPN) Solution for securing private data travelling over a public network is using

VPN VPN works by using encrypted data packets between a private network a

computer somewhere in the internet

Security methods with VPN User accounts and passwords are required, when the remote users sends

data to the authentication server, the data is encrypted using protocols such as EAP (Extensible Authentication Protocol), SPAP (Shiva Password Authentication Protocol) and others

After the user is authenticated, a tunnel is created so that all data sent between the user and the company is strongly encrypted

There are 4 tunnels protocol that can be used PPTP (Point to Point Tunneling Protocol) - weakest L2TP (Layer Two Tunneling Protocol) – strongest is combined with

IPSec SSL (Secure Socket Layer ) IPSec (IPSecurity)

Supporting Internet Client

Web browser is a s/w application on client PC used to request web pages from the web server on the internet

URL (Uniform Resource Locator)

http://www.facebook.com/photo/mypic.php

Protocol

Domain Name

Network Name

Host Name

folder filename

Using Secured Web Connection Using HTTPS (HTTP Secure) For Internet Banking or private business HTTP over SSL (Secure Socket Layer) or TSL (Transport Layer

Security) The purpose of these security protocols is to prevent others from

the internet to eavesdropping on data or change the data SSL – uses an encryption system that uses a digital certificate.

Public Keys are secret codes used to encrypt and decrypt the data. A digital certificate, or digital ID, digital signature is a code assigned to you by a certificate authority such as Verisign that uniquely identifies you on the net and includes a public key

TSL – improved version of SSL