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Instructions for TAs

This guide provides TAs with essential instructions related to TCP, DNS, and HTTP protocols. It includes practical steps to configure the ‘hosts’ file, understand packet termination methods, and ping various domains. You'll learn how to manipulate DNS entries, troubleshoot requests, and explore examples of HTTP responses. The document also clarifies concepts from lectures, discussing resource records, non-persistent connections, and state storage in HTTP. Ideal for those involved in teaching networking concepts and looking to reinforce their knowledge.

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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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