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Configuring DNS and Understanding HTTP Basics

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This document outlines essential instructions for TAs on setting up entries in the ‘hosts’ file and understanding DNS and HTTP protocols. It highlights the importance of the Domain Name System (DNS) as a distributed database that stores resource records. It provides specific IP addresses to add, including links to different domains such as Panda Express and the National Scrabble Association. Additionally, it discusses the HTTP request process, TCP connections, and basic ordering processes at a restaurant, promoting clarity on how web communication works.

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Configuring DNS and Understanding HTTP Basics

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  1. Instructions for TAs • Add these entries to your ‘hosts’ file: • 192.232.222.190 nsa.gov • 192.232.222.190 www.nsa.gov (also feel free to set up a dodgy DNS server etc.) • Burn these instructions after reading

  2. DNS and HTTP!

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

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

  5. 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

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

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

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

  9. Hostname works …

  10. 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=/ ...

  11. 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=/

  12. 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

  13. 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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