Decoding URLs and IP Addresses in the Computer Era

1. (Representation of …)URLs, IP addressesin the computer era 114 – Lecture 8

2. Static URL Access method Server and domain Path Document U-R-L http://www.wellesley.edu/Resources/about/index.html • Uniform Resource Locator • T. B-L wanted URI: Universal Resource Identifier • It tells you where something is located, i.e., the name of the server that has it • It also tells you how you could get it • gov - Government agencies • edu - Educational institutions • org - Organizations (nonprofit) • mil - Military • com - commercial business • net - Network organizations • ca – Canada • kz–…

3. Harvard Bits

4. Dynamic fake URL Dynamic URL Access method Access method Server and domain Server and domain Web program Web program and parameter Parameter URL invoking a web program http://www.db-url.com/website-monitor.html?gclid=CLfYzO_bq5QodzReMiw http://wiki.answers.com/Q/What_does_URL_mean

5. Web Server www.wellesley.edu Web Server cs.wellesley.edu e-mail Server firstclass.wellesley.edu Clients and Servers THE INTERNET download upload Client Computers

6. You have been enumerated • Every server is enumerated in an IP address • IPv4: 32 bits written as 4 decimal numerals up to 256, e.g. 149.130.12.213 (Wellesley College) • How many addresses can it represent? • IPv6: 128 bits written as 8 blocks of 4 hex digits each, e.g. AF43:23BC:CAA1:0045:A5B2:90AC:FFEE:8080 • How many addresses are in IPv6? • Client translates URLs to IP addresses, e.g. cs.wellesley.edu  149.130.136.19 • Uses authoritative sites for address translationa.k.a: “Domain Name Server” (DNS)

7. What is your IP address? IP: Internet Protocol

8. What is the Internet? “Ten movies streaming across that, that Internet, and what happens to your own personal Internet? I just the other day got...an Internet was sent by my staff at 10 o'clock in the morning on Friday. I got it yesterday [Tuesday]. Why? Because it got tangled up with all these things going on the Internet commercially. [...] They want to deliver vast amounts of information over the Internet. And again, the Internet is not something that you just dump something on. It's not a big truck. It's a series of tubes. And if you don't understand, those tubes can be filled and if they are filled, when you put your message in, it gets in line and it's going to be delayed by anyone that puts into that tube enormous amounts of material, enormous amounts of material.” Senator Ted Stevens, Chair, Comm. on Commerce, Science and Transportation(charged with regulating the internet)

9. What is the Internet?

10. No really, what is it? https://www.youtube.com/watch?v=ewrBalT_eBM

11. (Communicating through …)HTTP and TCP/IP Protocolsin the web era 114 – Lecture 9

12. A nuts and bolts view of Internet client • The Internet is a network of networks consisting of: • hosts (can be can be either clients or servers) • communication linksof varying bandwidths • routers (switching devices) • modems translate bits to travel correctly through wires and air • A client programrunning on a host, following a protocol, requests and receives a file from a server programrunning on another system • We call such programs processes routers modem server Network Protocols and HTTP

13. ARPAnet, 1971

14. Sending and receiving information Handshake Network Protocols and HTTP

15. TCP/IP vs Postal Mail Protocols TCP ~ Higher Level Protocols IP ~ Lower Level Protocols

16. TCP/IP: Basic Protocols • TCP: Transport Control Protocol • Creates logical connection b/w two machines on the network • Makes connected machines think that they are directly connected • Provides reliable, perfect transport of messages • IP: Internet Protocol • Breaks data into packets to move through routers • Tries hard, but may drop packets • We usually talk about TCP/IP • TCP uses IP and guarantees delivery

17. Message pipelining • When the message is segmented into packets, the network is said to pipeline message transmission.

18. Standards, although they are merely • conventions, give rise to vast innovation, if they are well chosen, spare, and • widely adopted.

19. Packet switching • Messages are broken into packets each of which travels from the source to destination through a maze of routers and links. • Packet switching achieves much higher efficiency than full-file travel

20. Traceroute from gaia.cs.umass.edu 3 delay measurements 1 cs-gw (128.119.240.254) 1 ms 1 ms 2 ms 2 border1-rt-fa5-1-0.gw.umass.edu (128.119.3.145) 1 ms 1 ms 2 ms 3 cht-vbns.gw.umass.edu (128.119.3.130) 6 ms 5 ms 5 ms 4 jn1-at1-0-0-19.wor.vbns.net (204.147.132.129) 16 ms 11 ms 13 ms 5 jn1-so7-0-0-0.wae.vbns.net (204.147.136.136) 21 ms 18 ms 18 ms 6 abilene-vbns.abilene.ucaid.edu (198.32.11.9) 22 ms 18 ms 22 ms 7 nycm-wash.abilene.ucaid.edu (198.32.8.46) 22 ms 22 ms 22 ms 8 62.40.103.253 (62.40.103.253) 104 ms 109 ms 106 ms 9 de2-1.de1.de.geant.net (62.40.96.129) 109 ms 102 ms 104 ms 10 de.fr1.fr.geant.net (62.40.96.50) 113 ms 121 ms 114 ms 11 renater-gw.fr1.fr.geant.net (62.40.103.54) 112 ms 114 ms 112 ms 12 nio-n2.cssi.renater.fr (193.51.206.13) 111 ms 114 ms 116 ms 13 nice.cssi.renater.fr (195.220.98.102) 123 ms 125 ms 124 ms 14 r3t2-nice.cssi.renater.fr (195.220.98.110) 126 ms 126 ms 124 ms 15 eurecom-valbonne.r3t2.ft.net (193.48.50.54) 135 ms 128 ms 133 ms 16 194.214.211.25 (194.214.211.25) 126 ms 128 ms 126 ms 17 * * * 18 * * * 19 fantasia.eurecom.fr (193.55.113.142) 132 ms 128 ms 136ms trans-oceanic link no response

21. HTTP: HyperText Transfer Protocol • HTTP is the Web’s client/server protocol. • User agent (browser) implements the client side of HTTP. • Web pages generally consist of an HTML file which references other objects (JPEG, Java applet, video, audio clips).

22. HTTP/1.0 nonpersistent connection http://www.someSchool.edu/someDir/file.html 1a.Client initiates a TCP connection to www.someSchool.edu 1b.Server at host www.someSchool.edu accepts connection and acknowledges. • Client sends HTTP request for file • /someDir/file.html 3. Server receives message, finds and sends file in HTTP response. Client receives response.terminates connection, examines file, and may request other files. 5. Steps 2, 3, 4 are repeated for each requested file.

23. HTTP request message request line (GET, POST, HEAD commands) GET /someDir/file.html HTTP/1.0 Host: www.someSchool.edu User-agent: Mozilla/4.0 Connection: close Accept-language:en,fr header lines Carriage return, line feed indicates end of message

24. HTTP response message status line (protocol status code status phrase) HTTP/1.0 200 OK Connection: close Date: Thu, 06 Aug 1998 12:00:15 GMT Server: Apache/1.3.0 (Unix) Last-Modified: Mon, 22 Jun 1998 …... Content-Length: 6821 Content-Type: text/html data data data data data ... header lines requested HTML file

25. Type: telnet cs.wellesley.edu 80 Type: GET /~mir/index.html HTTP/1.0 Opens TCP connection to port 80 Issues a GET request to HTTP server (you must hit carriage return twice at the end). Testing HTTP using telnet

26. 200 OK request succeeded, requested object in this message 301 Moved Permanently requested object moved, new location specified in this message (Location) 400 Bad Request request message not understood by server 404 Not Found requested document not found on this server 505 HTTP Version Not Supported Some HTTP response status codes

27. SMTP (mail) protocol The sending process must simply specify • the name or address of the host machine(hostname or IP address), and • The process on that host that will handle the received message (port number). • Mail port is usually 25