Intro To Web Technologies

Introduction to Web Technologies – Day 1 E&R Department, Mysore

Course Objective •

To introduce participants to the basic concepts of Inter-Networking, World Wide Web

•

To familiarize with the concept of Web Servers, various web servers and to illustrate the features of each of them

•

To introduce the concept of Web Applications, load balancing, Application servers and real world scenarios of Web Applications

•

To provide the overview of web security.

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Session Plan Day 1 • • • • • • • •

Introduction to the Networking and Internet TCP/IP protocol and IP Addressing Domain Name System Introduction to Firewall Virtual Private Network (VPN) Directory service and Active Directory Introduction to the World Wide Web Key terminologies of WWW

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Day 2 • • • • • • • • • •

Web Applications Web Servers Introduction to the Common Gateway Interface (CGI) Load Balancing Application Server Web Security Encryption Digital Certificates Performance of web Applications Appendix

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References •

History of the Internet – http://www.davesite.com/webstation/net-history.shtml

•

Apache Foundation – http://www.apache.org

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Introduction to Networking and Internet

Background • 1957: US Government Formed ARPA (Advanced Research Projects Agency) within DoD (Department of Defense) • 1962: The US DoD was looking at means to make all its computers to talk to each other to achieve better command and control and commissioned RAND Corporation to do a study on how it could be achieved • 1968: ARPA awarded the contract for ARPANET to BBN • ARPA got renamed as DARPA (Defence Advanced Research Projects Agency) • 1973: Development began on a protocol which was later to be named TCP/IP • This new protocol would allow diverse computer networks to communicate with each other • ARPANET would use TCP/IP protocol from here and would become the base for the Internet

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Who decides the Standards •

IAB (Internet Architecture Board) – – – –

An autonomous organization created in 1983 Evolved from the ARPA research group Managed by Volunteers Reorganized in 1986 • IETF – Internet Engineering Task Force • IRTF – Internet Research Task Force

– Documentation given out in the form of RFCs – RFC: (Request for Comments) • A set of technical and organizational notes about the Internet (originally the ARPANET), beginning in 1969

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Internet • • • •

One huge network of networks Millions of Hosts hooked on to the net Roughly 40 million users Uses TCP/IP Protocol

•

Means to connect to Internet – – – – –

Dial-up Line (Through telephone): Domestic users DSL (Through telephone): Domestic users Mobile Phones: Domestic users, Dedicated Links: Medium and small sized companies T1,T3 connections: Large Corporations

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Internet Contd..… Network 3 Server

Mainframe

Fremont PC

PDA

PC

Laptop

Network 4 Laptop

PC

PC Mainframe

Bangalore

PC

PC

Cell phone

Network 1

Sydney

PC

PC

Server

Plotter

Scanner

PC

Berlin Laptop

Printer

Fax

PC

TO OTHER NETWORKS

Minicomputer

Network 2

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Internet Service Providers (ISP) • ISP is a company which provides Internet access for individuals, organizations, and companies. • An ISP usually has multiple access methods, including dial-up, DSL, cable modem, ISDN, T1, and sometimes T3. • The service provider gives the user a software package, username, password and access phone number. Equipped with a modem, user can log on to the Internet and browse www and use net, and send and receive e-mail. • ISPs serve large companies, providing a direct connection from the company's networks to the Internet. • ISPs themselves are connected to one another through Network Access Points (NAP)

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TCP/IP Protocol •

Packet switching Protocol – Involves breaking down of data into Packets or Datagrams – Packets are labeled with origin and destination address – Packets are forwarded from one computer to other until it reaches the destination – If packets are lost, originator re-sends the packets

• •

Principles and ideas resulted from research funded by ARPA ARPA’s technology includes a set of standards to specify – How computers communicate? – What are the conventions to interconnect the networks? – How to route traffic?

• •

Interoperability: key reasons for TCP/IP TCP/IP is a packet-switched protocol

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What is packet switching? 192.168.121.40

G

iMac

Ethernet Card

Ethernet Card

Ethernet Card

Network

Ethernet Card

Ethernet Card

F

192.168.223.208

1111110000010010 0011111001000100 1010001000011111 0010101110010001 1110111111000001 0010010001000011 1110010101110010 0011110011111001 0001001010001000 0111110001000111 1001111100100011 1100111110111001 Data /File

192.168.121.40 192.168.223.208 4 10100010000111.. 192.168.121.40 192.168.223.208 ` 3 00100100010000.. 192.168.121.40 192.168.223.208 2 0111110001000.. 192.168.121.40 192.168.223.208 1 1100111110111..

Packets 192.168.121.40 192.168.121.40 192.168.121.40 192.168.121.40 192.168.223.208 192.168.223.208 192.168.223.208 192.168.223.20 1 2 4 3 1100111110111.. 0111110001000.. 10100010000111.. 00100100010000.

Ethernet Card F

192.168.223.208

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1111110000010010 0011111001000100 1010001000011111 0010101110010001 1110111111000001 0010010001000011 1110010101110010 0011110011111001 0001001010001000 0111110001000111 1001111100100011 1100111110111001

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TCP/IP Model

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Internet Protocol Address • • • •

A 4-byte network addressing scheme used by the IP layer Within a private or closed network, one can assign any IP address Every Internet host must have a distinct IP address It has two components, – Network ID – Host ID

• •

IP address is provided by the Internet service provider IP addresses are a scare resource!!

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IP Addressing scheme Class B w

x

y

NETWORK ID

z HOST ID

EXAMPLE: 130.99.128.25 1 0 0 0 0 0 1 0 1 1 0 0 0 0 1 1 1 0 0 0 0 0 0 0 0 0 0 1 1 0 0 1

Class

Range

Remarks

A

1.0.0.0 to 126.0.0.0

B

128.0.0.0 to 191.255.0.0

C

192.0.1.0 to 223.255.255.0

D

224.0.0.0 to 239.255.255.255

(Multi-Casting)

E

240.0.0.0 to 247.255.255.255

(Reserved for future use)

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Classes of Networks NUMBER OF N/Ws

NUMBER OF HOSTS

z

126

16,777,214

z

16,384

65,534

z

2,097,152

254

Class A w

0

x

NETWORK ID

y HOST ID

Class B 1 0

w

x

y

NETWORK ID

HOST ID

Class C 1 1 0 w

x NETWORK ID

y

HOST ID

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DHCP (Dynamic Host Configuration Protocol) STATIC IP CASE

Computer Boots up (Assumes Static IP addr set by Admin)

Other Computers on Network. LAN

Server

Sys Admin Ensures that IP address is unique for all nodes IBM Compatible

DYNAMIC IP CASE Assigns IP address and other config info User Dials into the network (Connect)

Modem

P sI d n g an fo si As ress ig in f d Ad r con e oth

DHCP SERVER

LAN Computer Boots up (Broadcasts on the Network)

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Server

IBM Compatible

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Other Computers on Network.

Sub-Netting

Default IP Address Definition Internet ID

Host ID

1 0 0 0 0 0 1 0 1 1 0 0 0 0 1 1 1 0 0 0 0 0 0 0 0 0 0 1 1 0 0 1 Internet ID

Host ID

Sub-Netting Physical Network

• •

To create sub-networks within a given IP address range Changes interpretation of IP Address slightly – Extend the network portion of IP address into the Host Part

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Dividing Local Part is flexible The 32 bit Subnet mask decides how many bits are used for Physical Network ID and how many for host ID. Copyright © 2004, 19 Infosys Technologies Ltd

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Subnet Mask

130

99

128

25

IP Address 1 0 0 0 0 0 1 0 1 1 0 0 0 0 1 1 1 0 0 0 0 0 0 0 0 0 0 1 1 0 0 1 Internet ID

Host ID Physical Network

Subnet Mask

1 1 1 1 1 1 1 1 1 1 1 111 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 3 Bits

255

255 Copyright © 2004, 20 Infosys Technologies Ltd

5 Bits

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Domain Name Servers • •

It’s too difficult to remember IP Addresses Domain Name – Hierarchical name space – Last word in Domain name typically identifies type of organization or country

•

Domain Name Servers – Translates Domain Name to IP Address – De-Centralized naming – Delegation of authority to portions of name space • Example:137.107.2.24 = petshop.com • Email ID: [email protected]

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Internet vs Intranet •

Internet – Not owned by any single entity – Have publicly known IP addresses (Unique world-wide)

•

Intranet – – – – – –

Used by corporations for their own business or operational needs Usually accessible only to the members, employees of the organization Use the same technology as Internet Smaller in size Private networks Better Controlled and More secure

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Secure networks

Virtual Private Network (VPN) • • • • • •

Secure Private communication over public internet Private IP packets are encapsulated with in public packets (Tunnels) Additional header added Authentication Private packets may also be encrypted (Desirable) Option of disabling access to local LAN resources when VPN connection is active • Running VPNs across the internet offers a cost effective solution • Alternates: Dedicated links, Leased lines Uses of VPN: • Leased lines are expensive • VPN is used as a secure mechanism to connect to a remote network • Users on the go use VPN to access their corporate network • Companies use VPN to connect to customer’s network

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VPN – How it works? (1 of 2)

Infosys Customer Belgium

Switch

Printer

Laptop Mainframe

PC

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Laptop

VPN – How it works? (2 of 2) •

Overview of how VPN works – Secured communication channel between intranets over the internet – Works on the concept of tunnelling • Enclosing one protocol within another

– Configurable •

Typical high security environments disable local network access

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Proxy Servers • • •

Multiplexing outbound requests through a single connection Typically used to address Outbound traffic security Support incoming traffic as well Eg. • There may be restrictions to visit certain sites from within a corporate network, such rules may be imposed at the proxy server layer • Also, there may be restrictions in accepting certain kinds of files within an intranet domain from outside, these are also monitored by the proxy server

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Fire Wall • • • •

A system designed to prevent unauthorized access to or from a private network. Can be implemented in both hardware and software, or a combination of both. Frequently used to prevent unauthorized Internet users from accessing private networks connected to the Internet, especially intranets. All messages entering or leaving the intranet pass through the firewall –

Messages are examined and those that do not meet the specified security criteria are blocked

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Fire Walls

2 a. If the packet doesntadhereto securitypolicy,itis rejected 1. Anypacketfrom the intranetto outside networkisexamined byfirewall

The Intranet

Web Server 2b.Ifpacketadheresto securitypolicy,itis forwarded

File Server

The Internet

3.Firewallsexaminesall incoming packetsaswell.

SecurityPolicy implemented on the firewall

Database Server

Application Server

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Types of Fire walls 1. IP Filtering Firewalls: – Works at the packet level. – Designed to control the flow of packets based the source, destination, port and type information in each packet. – Evaluates the packets against a series of predefined rules to determine when to allow or deny the access of specific packets to the internal network 2. Packet filtering on Proxy Servers – Provides the tighter security than normal servers. – Mostly used to control, or monitor, outbound traffic. – Uses additional controls so that only specific hosts can access to the server. – Listens for requests from clients within the firewall and forwards these requests to remote internet servers outside the firewall

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World Wide Web

Background • • • • • • • •

The origin of internet is the ARPANET For many years it had a text based User Interface 1989 – Introduction of World Wide Web (WWW) Wide area information retrieval project in 1989 by Tim-Berners-Lee Initial Proposal: Hypertext system to enable easy information sharing among researchers Line Browser (called www) in 1990 NCSA Mosaic browser in 1993 1994… Marc Andreessen starts Netscape

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Overview

File System

Web Server HTML Pages GIF/JPG Images etc

Web Gateway Database Non-Web Content (Dynamic Content) Copyright © 2004, 33 Infosys Technologies Ltd

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Web Browser Architecture Mime-type Mapping app/pdf - acroread.exe video/mpeg mplayer.exe

Driver

HTML Interpreter /Renderer Keyboard

Controller

Optional Interpreter Optional Interpreter Optional Interpreter /Renderer /Renderer /Renderer

Mouse Optional Client Optional OptionalClient Client Other

HTTP

HTTP Client

TCP/IP

Network Interface

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Monitor

MIME-Type • • • • •

Defined in 1992 by IETF MIME – Multipurpose Internet Mail Extensions Originally designed for formatting non-ASCII messages so that they can be sent over the internet via mail Browsers and Web Servers also rely on mime-type to determine the type of content Examples of mime types – – – –

•

text/plain – Plain text text/html – HTML data app/pdf – Adobe Acrobat Document video/mpeg – MPEG format video file

A new version called S/MIME supports encrypted messages

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Constituents of World Wide Web • • • • • • •

Web Browsers Web Content Web Site URL – Uniform Resource Locator HTTP – Hyper Text Transfer Protocol HTML – Hyper Text Markup Language Gateway to Non-Web Resources (Common Gateway Interface )

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Types of Content •

Web Content (Static Content) – – – – –

Content resides in a file Author determines the content at the time of creation Each request will return exactly the same data (Content doesn’t change) Example: HTML files, gif/jpeg files Disadvantage: Not possible to implement applications

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Types of Content (Continued…) •

Dynamic Content – – – –

•

Created on the fly by a web server upon a request to reflect the current info Content may vary for each request Example: A typical web application (Banking etc) Disadvantage: More processing power required on the server

Active Content – – – – –

Server returns a run-able copy of the program Browser executes the program locally on the client machine May need continuous information feed Examples: Java Applets, Active-X controls for IE Disadvantage: Possible Security risks

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URL • •

Uniform Resource Locator String of characters that uniquely identifies a resource

Protocol:// Host :Port / Path Protocol: The protocol to be used (http, ftp, gopher…) Host: Domain Name/IP Address that identifies the host Port: Optional port (if not specified assumes default port for protocol) Path: Path of the resource on the specified host Example: http://server1.mydomain.com/about.html Protocol = http Host = server1.mydomain.com port = (default for http) 80 Path = /about.html Copyright © 2004, 39 Infosys Technologies Ltd

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HTML •

Hyper Text Markup Language – – – –

•

Uses markup tags to format text and graphics Allows creating of hyper links Allows users to navigate through the documents on the web All browsers can understand HTML and render it

An Example HTML file

A HTML Page

This is a sample HTML page which demos Bold, italic text and a table.

1	Row-1
2	Row-2

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HTTP Protocol

HTTP Protocol • • • • • •

Simple Request-Response model based protocol Application Layer protocol built on TCP/IP Plain-text protocol (Not Secure) Stateless Protocol Does not define how network connection is initiated or managed Standardized (Allows any Vendor’s HTTP client to communicate with any vendor’s server)

• •

Client sends a request to the server (HTTP Request) Server sends a response to the client (HTTP Response)

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HTTP Request •

A HTTP Request can have – An Initial Line (Method, URL, Protocol Version) – Zero or more Header lines (Client information, configuration, acceptable formats of data) – A Blank line – An optional message body (Additional Data – to be used by HTTP POST method)

•

Example: http://www.infosys.com/usr/index.html GET /usr/index.html HTTP/1.0 User_Agent: Mozilla/3.0 Gold Accept: text/plain Accept: text/html

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HTTP Methods •

GET method – Parameters are encoded and passed along with the URL – URL encoding – In web usually, parameters are passed as name-value pairs • Example: http://abcbooks.co.in/cgi-bin/getinfo.exe?title=Web+Servers

•

POST method – The parameters from the browser are passed as part of the Message body – Typically the CGI program receives the message body through STDIN and decodes it – HTTP response for POST is usually a program output

•

HEAD method – Gets just the header information from the server – Usually used to get only information about the content – Helps save on bandwidth

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HTTP Response •

A HTTP Response can have – An initial line or Status Line (Server HTTP Version, Status Code, Reason) – Headers – (Typically contain description of information in the response) – Message Body (The requested information)

•

Example: Response for /usr/index.html HTTP/1.0 Status 200 OK Server: NCSA/2.0 Date: Wed, 05 May 2004 16:00:04 GMT Content-type: text/html Content-length: 2400 … Copyright © 2004, 45 Infosys Technologies Ltd

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HTTP Versions •

HTTP 1.0 – A new connection is established for every request – Closes the connection to server once the server sends the required data

•

HTTP 1.1 – Once a connection is established, it is maintained till the browser is closed

(Also known as persistent connection) – Allows server side session management even though the HTTP protocol itself doesn’t support it

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Advantages/Disadvantages of HTTP •

Advantages – Very simple to use – Very Flexible (Can be used to send other types of data as well) – Easy and lightweight to implement

•

Disadvantages – No support for session management at the protocol level – Less secure

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Web Servers

Process, Thread, Daemon Process, Server • •

Process: An instance of an application in memory. Thread: Basic unit of program execution – An independent code path within your program – Common example: MS Word – Spelling and Grammar check – Servers rely on threads

•

Daemon process (Background Process): Starts when OS starts up – They cannot be terminated by any user process – In Unix, runs typically with either ‘root’ or specific user-id created for the daemon process – Windows NT equivalent: Windows Services

•

Server: A software, that provides specific services to client programs – Clients can run either on the machine or different machine – Examples: Web Server (Sparsh), Mail Server etc – Servers are typically implemented as a Daemon process • Servers employ threads for multi-processing

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Working of a simple client and server Server REQUEST Param: Service Name Additional Parameters Client

RESPONSE Status Requested Data

Assign a thread to service the request

vice t r e S ues Service1 Service2 ReqThread Pool k to c a rn b l u t Re Poo

File System Configuration File 1. Thread Pool size 2. Service configuration 3. Other Parameters

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Web Server • • • • • •

Understands HTTP Protocol It intercepts HTTP request from the client Built on similar architecture as a classic client -server architecture Offers different HTTP services like GET, POST, HEAD etc. Uses thread pools to service multiple concurrent requests Originally designed to serve HTML, image and other files – Evolved as a mechanism to share documentation among researchers

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Working of a Web Server

DNS Server (Local Network)

3. Cannot Resolve Locally? Resolve from other DNS

2. Translate DNS 4. Returns IP Addr Name to IP address 202.68.33.47

1. User Invokes URL http://my.mydomain.com/ test.html

on cti d e n on lishe C . 6 tab Es

The e Internet th ru h t ns r t ath tai ec erve P n n on to s (co for C t e . s s l) 5 n/w e on .htm qu l p e s t R Re f tes TP t.htm P T o T H /tes HT ents nd d e t n S Se con 7. 8.

Web Server (Internet) my.mydomain.com 202.68.33.47

9. Browser Renders Web Browser HTML

PC

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Developer’s role in this scenario - 1(Static Content) •

Installation of Web Server Software – Both commercial and Open source Web Servers • Web Servers: iPlanet, IIS, Apache Web Server (Open Source, available on many platforms)

•

Configuration of Web Server Software – Typical configuration parameters • TCP/IP Port by default is 80 and TCP/IP port is also 80 • Web Server Root • Thread Pool size, Performance parameters

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Developer’s role in this scenario – 2 (Static Content) •

Developing Content – Create HTML files • Applications to use: Notepad or any text editor, MS Front Page, Netscape Composer…

– Create JPEG or GIF images • Applications to use: Windows Paintbrush (GIF, JPEG and PNG Formats supported), GIMP (Open Source, available on many platforms), Adobe Photoshop etc

•

Domain Name/Server Name registration (if required) – Registering with Domain Name Providers (Internet) – Registering with DNS (Intranet)

•

Debug and Test

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Summary • • • •

Networking and Internet Protocols like TCP/IP, HTTP etc Domain Name System Secure Networks – VPN – Proxy Servers – Firewalls

• •

World Wide Web HTTP Protocol

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Thank You! Copyright © 2004, 56 Infosys Technologies Ltd

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