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How does the Internet work ?
How does the Internet work ?
How does the Internet work ?
How does the Internet work ?
How does the Internet work ?
How does the Internet work ?
How does the Internet work ?
How does the Internet work ?
How does the Internet work ?
How does the Internet work ?
How does the Internet work ?
How does the Internet work ?
How does the Internet work ?
How does the Internet work ?
How does the Internet work ?
How does the Internet work ?
How does the Internet work ?
How does the Internet work ?
How does the Internet work ?
How does the Internet work ?
How does the Internet work ?
How does the Internet work ?
How does the Internet work ?
How does the Internet work ?
How does the Internet work ?
How does the Internet work ?
How does the Internet work ?
How does the Internet work ?
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How does the Internet work ?

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Transcript

  • 1.  
  • 2. What we will cover
    • What is the Internet
    • Client/server examples
    • Deciphering alphabet soup: ISP, DHCP, DNS, http, https, HTML, smtp, pop3, telnet, ftp, sftp, ssh
    • Network security:
      • How to send anonymous emails
      • How to hack into a system
      • How a Firewall works
      • Encrypted communications
  • 3. Internet History
    • The Internet is a global network of interconnected computers, enabling users to share information along multiple channels.
    • http://en.wikipedia.org/wiki/Internet
    • Started in 1969 as ARPANET funded by DARPA (Defense Advanced Research Projects Agency)
    • Build as packet switching network to recover from a nuclear attack by automatically rerouting data through surviving links
    • “ When I took office, only high energy physicists had ever heard of what is called the World Wide Web... Now even my cat has it's own page.” Bill Clinton
  • 4. The User Perspective
    • have little laptop at home in NJ
    • want to exchange information with big server in California (or Japan or …)
  • 5. Basic Setup
    • Each computer must have a unique identifier
      • IP number and IP name
    • Computers must be able to exchange data (electrons, photons, drum beats)
      • Wireless cards, fiber optics, or Ethernet connections
      • Unit of data is “ bit ” (“zero” or “one”, on/off, 2 states)
    • Everyone involved must speak the same language
      • TCPIP (Transmission Control Protocol/Internet Protocol)
  • 6. Network Member Identifier
    • Every computer on the Internet has at least one unique identifier, usually two:
      • IP Number: #.#.#.#, where # is an 8 bit number
        • What is the range for each sub-number?
        • How many machines can be on the Internet?
        • What is your computer’s IP number?
      • IP Name for easy reference
        • What is your computer’s IP name?
      • Homework :
        • What is the IP number of “google”
        • What is the IP number of “www.shu.edu”
        • What is the IP name of “149.150.254.102”
  • 7. ISP DHCP Router A Router B DNS www.google.com fiber optic lines ISP: Internet Service Provider DHCP: Dynamic Host Config. Protocol DNS: Domain Name Server
  • 8.  
  • 9. The Data: IP Packet www.google.com (66.102.1.147) (149.150.254.102)
  • 10. The Data: IP Packet www.google.com (66.102.1.147) (149.150.254.102)
  • 11. The Protocol
    • A mutually agreed-upon convention or standard that controls or enables the connection, communication, and data transfer between computing endpoints.
    • http://en.wikipedia.org/wiki/Protocol_(computing)
    • Regulates the data exchange and interpretation
    • Defines who says what at which time
    • Defines how to interpret data that is exchanged
    • Regulates what constitutes an error and what to do if one occurs
  • 12. Client – Server Model
    • Communication on the Internet usually takes place between a client and a server program/computer:
      • Server program : program without a user interface running on a “large” computer with access to many resources (also called the server computer)
      • Client program : a program with extensive interface capabilities but few resources running on a “small” computer (also called the client computer)
    • One server computer usually run several server programs , each of which can service multiple client programs simultaneously
  • 13. Client – Server Example (1)
    • I want to view the main web page from www.shu.edu
    • Server computer : www.shu.edu
    • Client computer : 192.168.1.2
    • Server program : web server program (httpd) running on www.shu.edu with access to lots of stored web pages
    • Client program : Internet Explorer or Firefox with extensive formatting and display capabilities but no data to display
  • 14. Client – Server Example (2)
    • I want to view the main web page from www.shu.edu
    • Client : start IE and enter: http://www.shu.edu/
      • Client sends packet to DNS: who is www.shu.edu
      • DNS sends packet back: www.shu.edu = 149.150.51.69
      • Client sends packet to 149.150.51.69: give me main page
    • Server: receives request for page from 192.168.1.2
      • Retrieves the web page from disk (or database)
      • Sends data to 192.168.1.2: here is the data
    • Client : formats data and display it nicely
  • 15. Client – Server Example (3)
    • I want to view the main web page from www.shu.edu
    • Client: sends “ give me main page ” Server: sends data to 192.168.1.2
      • http ( H yper t ext T ransport P rotocol): regulates how a web server and client communicate
    • Client : formats data and display it nicely
      • HTML (Hypertext Markup Language): defines how text is supposed to look and where to place it
  • 16. Client – Server Example (4)
    • I want to view the main web page from www.shu.edu
    Action http 1.0 specs http uses port 80 by general agreement Client: “give me main page” GET / HTTP/1.0   Server : returns data fixed header: how many bytes are coming, type of data   page text ...
  • 17. Client – Server Example (5)
    • Telnet:
    • universal text client used to connect to another computer and work on that computer in text-based mode
    • usually connects to a “telnet server” but can also connect to any server computer and any server program
    • shows text data in ‘raw’ unformatted form
  • 18. Client – Server: Telnet
    • A Telnet client is build into Windows:
      • Click on “Start”
      • Pick “Run …” and type “cmd”
      • Type “telnet”
        • if you get error message in Vista, open Control Panel, select “Programs”, click “Turn Windows features on or off”, and check “Telnet client” (not “Telnet server”). Then try again.
      • To open a connection to www.shu.edu, type:
          • open www.shu.edu (will this work – why not?)
      • Optional: to save a log of your session, type:
          • set logfile log.txt
  • 19. Telnet’ing to a Web Server
    • Start “telnet” and type:
        • open www.shu.edu 80
    • Next type carefully and without errors (you might not see what you type on the screen – type anyway, including the empty line and capitals):
        • GET / HTTP/1.0  
    • You have issued a request according to the Hypertext Transfer Protocol , version 1.0, for the root web page /
  • 20. How email works
    • Email systems have two parts, and consequently work with two server programs and two protocols:
    • Retrieving email
      • uses either pop3 (Post Office Protocol version 3 on port 110) or IMAP (Internet message access protocol on port 143)
    • Sending email
      • uses smtp (simple mail transport protocol on port 25)
  • 21. An smtp Conversation Speaker Text Server: 220 Simple Mail Transfer Service ready Client: HELO mycomputer.mydomain Server: 250 kitten.shu.edu Client: MAIL FROM:<Smith@shu.edu> Server: 250 OK Client: RCPT TO:<Jones@shu.edu> Server: 250 OK Client: DATA Server: 354 Start mail input; end with <CRLF>.<CRLF> Client: Blah blah blah.. . Server: 250 OK Client: QUIT
  • 22. Homework
    • Capture a web page from a web server
    • Send me an (anonymous) email using Telnet (note that the SHU smtp server will only allow a connection if you are located on campus – how does it know?)
  • 23. Hacking 101
    • Identify a target system
    • Find an open port
    • Check which server program services that port
    • Learn about vulnerabilities of that server program
    • Exploit vulnerability for evil purposes
  • 24. Firewall Protection
    • Every packet transported over the Internet contains the protocol ( port ), sender address , and destination address
    • A firewall is a device that inspects every incoming (and outgoing) packet and includes rules to block data depending on the port, sender, or destination
    • A firewall is typically integrated into a home wireless router
    • Most firewalls do not check the content of a packet
    ISP
  • 25. SPAM Protection
    • Every Internet packet contains the port, sender, destination, and content (data) – usually unencrypted
    • A SPAM filter is a device that inspects all email packets and includes rules to block messages depending on the content of the email.
    • A SPAM filter is typically integrated into you ISP or email provider
    • SPAM filters typically read your email!
    ISP
  • 26. Privacy/Content Protection
    • All Internet traffic is public!
    • To protect content, the data portion of IP packets must be encrypted
      • To protect data between your wireless router and your laptop, use e.g. WPA wireless encryption
      • To protect data after it leaves your router, you must use encrypted services ( https instead of http or sftp instead of ftp)
      • Note: no standard encryption for email!
      • Sending email is like passing a postcard along a chain of hundreds of people with a note: “to Jane – do not read if you’re not Jane”
    ISP
  • 27. Encryption
    • Encryption is usually based on a key that used to encrypt and decrypt a message.
    • Pre-Shared Key (PSK) Encryption:
      • both parties know a single key (e.g. WPA encryption: both your router and your computers know the key)
    • Public Key Encryption:
      • each party has two keys, a public and a private one. They swap public keys: Bob uses Annie’s public key to send her an encrypted message, she can decrypt it using her private key
      • based on difficulty of factoring huge numbers into large primes and ease of multiplying them
      • See http://www.explainthatstuff.com/encryption.html
  • 28. Public Key Encryption requires:
      • large “semi”-prime number x = p q
      • Example :
      • public key x = 15 => private key is:
      • Homework : Find factorization of RSA-100, which is 1522605027922533360535618378132637429718068114961380688657908494580122963258952897654000350692006139
      • More Info:
      • http://en.wikipedia.org/wiki/Public-key_cryptography
      • http://en.wikipedia.org/wiki/RSA_numbers
      • http://primes.utm.edu/mersenne/
      • Enigma by Robert Harris, and Enigma the Movie

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