Web Fundamentals

Web Fundamentals 4 th September 2007 WWW, Internet, and other weird stuff

This is not a presentation

But more of a Discussion

Maximum questions

Maximum answers (if possible)

You are allowed to sleep

You will get a copy of these slides

But slides are less important.

Exercises will be there

What is Internet?

Internet is a global network of smaller networks.

Internet is the largest network.

It is owned by NOBODY

Smaller network: 1-1000 computers

Satellites, Submarine Optical cables

Backbone

The biggest name is Cisco

What is (the) Web?

You mean World Wide Web?

Collection of interlinked hypertext documents.

That means Hyperlinked documents

Hyperlinks?

URL

HTTP?

HTTP is an application level protocol for transferring data through WWW.

Hyper Text Transfer Protocol

HTTP 0.9 / 1.0 / 1.1 / 1.2

HTTPS (S for Secure)

HTML – Header, content.

They say HTTP is stateless.

DNS

DNS is like post office

Some post offices will be knowing some addresses

DNS servers will have addresses like this www.google.com => 64.67.33.200

Multiple Name servers for reliability

Domain Name

Netkode.com

Mail.netkode.net

Abc.mail.netkode.net

http://mail.netkode.net/

http://mail.netkode.net:80/

http://mail.netkode.net:80/inbox/index.jsp

Port

A simple web request Browser Name Server Internet Web Server IIS, Apache, Lighttpd etc. BIND, PowerDNS, djbdns HTTP Response DNS Lookup http://bookmarks.rediff.com/recent/ bookmarks.rediff.com => 210.210.93.86

Cookies

Comes in different flavors

Through HTTP Headers

Persistent Cookie

Session Cookie

Secure Cookie

HTTP Only Cookie

3 rd Party Cookie

How Cookies work? 2) Response from Web server 3) 2 nd request from browser 1) Request from Browser GET /index.html HTTP/1.1 Host: bookmarks.rediff.com HTTP/1.1 200 OK Content-type: text/html Set-Cookie: name=value; expires=date; path=/; domain=.rediff.com (content of page) GET /popular/ HTTP/1.1 Host: bookmarks.rediff.com Cookie: name=value Accept: */* expires=Fri, 31-Dec-2027 23:59:59

Session

One type of state management mechanism

A number of continuous request response sequences.

The key is called SESSIONID

PHPSESSID, ASPNETSESSIONID, jsessionid, SESSION_ID, mySESSID

GET /popular/ HTTP/1.1 Host: bookmarks.rediff.com Cookie: PHPSESSID=4dy1q2e3d44c5dj343s3aq9

Moral of the story

Programming languages are like religions

All say same things

Pray to same gods

Keep up your spirits

Session Security

Session id is like your browser’s password

‘non-guessable’ session id- even you can’t

Random numbers?

‘Yet to solve’ mathematical problem.

X is your ultra top secret algorithm.

X sessionid CPU temperature Current date time Other junk stuff

Session Security

And this algorithm can be as simple as MD5 or SHA1

These are called random hash code

Irreversible id => pseudo random id

Irreversible (only theoretically)

Forms

Method for data transfer from client to server (part of HTTP methods)

GET and POST

GET

Through URL

Limited data

POST – through HTTP Headers

More (complex) data

HTTP Error codes

1xx – Informational

2xx – Success

200 OK

3xx – Redirection

304 Not Modified

4xx – Client Error

404 Not Found

5xx – Server Error

500 Server Error

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