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Instructions for TAs

Instructions for TAs. Add these entries to your ‘hosts’ file: 67.18.184.147 nsa.gov 67.18.184.147 www.nsa.gov (also feel free to set up a dodgy DNS server etc.) Burn these instructions after reading. Finishing off TCP. DNS and HTTP!. plus. aka how to make a website!. ACK. ACK. FIN.

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Instructions for TAs

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  1. Instructions for TAs • Add these entries to your ‘hosts’ file: • 67.18.184.147 nsa.gov • 67.18.184.147 www.nsa.gov (also feel free to set up a dodgy DNS server etc.) • Burn these instructions after reading

  2. Finishing off TCP DNS and HTTP! plus aka how to make a website!

  3. ACK ACK FIN FIN Normal Termination:One Side At A Time • If Anand wished to disconnect acrimoniously, what packet could he send instead? Panda ACK SYN ACK SYN ACK Data Anand time Figure: slide 80, lecture 12

  4. http://www.pandaexpress.com • ‘ping www.pandaexpress.com’: 65.91.7.210

  5. http://65.91.7.210 • ‘ping www.pandaexpress.com’: 65.91.7.210

  6. Defending Our Nation.Securing The Future. • DNS: DDB of RRs • “Domain Name System: distributed database storing resource records” • Format: (name, value, type, ttl) • Types: • A • NS • PTR • CNAME • MX

  7. http://www.nsa.gov • What’s wrong? • Why isn’t this the National Scrabble Association?

  8. http://www2.scrabble-assoc.com • ‘ping www2.scrabble-assoc’: 64.77.84.73

  9. 64.77.84.73 • ‘ping www2.scrabble-assoc’: 64.77.84.73

  10. Hostname works …

  11. Unmasking the stealthy NSA $ telnet 64.77.84.73 80 GET / HTTP/1.0 HTTP/1.1 400 Bad Request Content-Type: text/html Date: Wed, 17 Oct 2012 04:13:42 GMT Connection: close Content-Length: 39 <h1>Bad Request (Invalid Hostname)</h1>Connection to 64.77.84.73 closed by foreign host. $ telnet 64.77.84.73 80 GET / HTTP/1.0 Host: scrabble-assoc.com HTTP/1.1 200 OK Connection: close Date: Wed, 17 Oct 2012 04:30:21 GMT Server: Microsoft-IIS/6.0 X-Powered-By: ASP.NET Content-Length: 17644 Content-Type: text/html Set-Cookie: ASPSESSIONIDQSAQDTQA=GMLHAOPCHHHFEEJCJCNEDMIO; path=/ ... See also slide 70, lecture 13 (“Multiple Sites Per Machine”)

  12. HTTP is Stateless • When would we want to store state? • How/where? • What principle does this follow from? HTTP/1.1 200 OK Connection: close Date: Wed, 17 Oct 2012 04:30:21 GMT Server: Microsoft-IIS/6.0 X-Powered-By: ASP.NET Content-Length: 17644 Content-Type: text/html Set-Cookie: ASPSESSIONIDQSAQDTQA=GMLHAOPCHHHFEEJCJCNEDMIO; path=/ See also slide 51 (lecture 13) + slide 64 (lecture 4)

  13. Non-persistent TCP connection TCP SYN 1 RTT TCP SYN-ACK 1 RTT + transmission TCP ACK + HTTP REQUEST TCP ACK TCP ACK + HTTP RESPONSE TCP FIN TCP FIN-ACK TCP ACK

  14. Easy ways to order! 3 4 2 1 • Go to store • Order burger • Go to store • Order drink • Go to store • Order fries • Go to store • Order burger • Order drink • Order fries • Go to store • Order burger, drink and fries • Go to store with two friends • Each person orders one item (in parallel)

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