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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.

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Presentation on theme: "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."— Presentation transcript:

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

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

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

4 ‘ping

5 ‘ping

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

7 What’s wrong? – Why isn’t this the National Scrabble Association?

8 ‘ping www2.scrabble-assoc’:

9 ‘ping www2.scrabble-assoc’:

10 Hostname works …

11 Unmasking the stealthy NSA $ telnet GET / HTTP/1.0 HTTP/ Bad Request Content-Type: text/html Date: Wed, 17 Oct :13:42 GMT Connection: close Content-Length: 39 Bad Request (Invalid Hostname) Connection to closed by foreign host. $ telnet GET / HTTP/1.0 Host: scrabble-assoc.com HTTP/ OK Connection: close Date: Wed, 17 Oct :30:21 GMT Server: Microsoft-IIS/6.0 X-Powered-By: ASP.NET Content-Length: Content-Type: text/html Set-Cookie: ASPSESSIONIDQSAQDTQA=GMLHAOP CHHHFEEJCJCNEDMIO; 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/ OK Connection: close Date: Wed, 17 Oct :30:21 GMT Server: Microsoft-IIS/6.0 X-Powered-By: ASP.NET Content-Length: Content-Type: text/html Set-Cookie: ASPSESSIONIDQSAQDTQA=GMLHAOP CHHHFEEJCJCNEDMIO; path=/ See also slide 51 (lecture 13) + slide 64 (lecture 4)

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

14 Easy ways to order! 1.Go to store 2.Order burger 3.Go to store 4.Order drink 5.Go to store 6.Order fries 1.Go to store with two friends 2.Each person orders one item (in parallel) 1.Go to store 2.Order burger, drink and fries 1 1.Go to store 2.Order burger 3.Order drink 4.Order fries 2 34


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