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The Domain Name System and DNS Blocking Malcolm Hutty Head of Public Affairs, LINX February 2011.

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1 The Domain Name System and DNS Blocking Malcolm Hutty Head of Public Affairs, LINX http://publicaffairs.linx.net February 2011

2 About LINX A membership association for network operators Based in London, UK One of the largest Internet Exchanges in the world – 400 member networks from over 50 countries – Over 1.2Tb/s peak traffic – Over 70% global Internet routes Public policy role in EU through

3 The voice of Internet Services Providers in Europe Represents over 1800 ISPs Umbrella structure: – National associations are EuroISPA members – Governed by a Board with one member per association Supported by an advisory forum of large multi-national network and service providers

4 www.example.eu 1. User types domain name into browser

5

6 2. Browser asks Access Provider for IP address of www.example.eu What’s the IP address for www.example.eu? Access Provider DNS Resolver

7 3. DNS Resolver asks Root Name Server for IP of a DNS server for.eu Root Name Server Where’s the.eu registry DNS server? Access Provider DNS Resolver

8 3. DNS Resolver asks Root Name Server for IP of a DNS server for.eu Root Name Server It’s at IP address: 198.51.100.56 It’s at IP address: 198.51.100.56 Access Provider DNS Resolver

9 4. DNS Resolver asks.eu DNS server for IP of the DNS server for example.eu.eu Registry DNS server Where’s the DNS server for example.eu? Access Provider DNS Resolver

10 4. DNS Resolver asks.eu DNS server for IP of the DNS server for example.eu.eu Registry DNS server It’s at IP address: 203.0.113.185 It’s at IP address: 203.0.113.185 Access Provider DNS Resolver

11 5. DNS Resolver asks for the IP address for www.example.eu … DNS example.eu What’s the IP address for www.example.eu? Access Provider DNS Resolver

12 5. DNS Resolver asks for the IP address for www.example.eu … DNS example.eu It’s at IP address: 192.0.2.12 It’s at IP address: 192.0.2.12 Access Provider DNS Resolver

13 6. … and passes the IP address back to the browser The IP address for www.example.eu is: 192.0.2.12 Access Provider DNS Resolver

14 7. … which contacts the website host using the IP address Contacting 192.0.2.12

15 8. HTTP traffic begins www.example.eu 192.0.2.12 Access Provider DNS Resolver

16

17 How DNS blocking works What’s the IP address for www.example.eu? Access Provider DNS Resolver

18 How DNS blocking works No such domain. Access Provider DNS Resolver

19 How DNS blocking works Or…

20 How DNS blocking works What’s the IP address for www.example.eu? Access Provider DNS Resolver

21 How DNS blocking works Access Provider DNS Resolver It’s at (cough) IP: 203.0.113.234 (cough) It’s at (cough) IP: 203.0.113.234 (cough)

22 How DNS blocking works Police controlled server Access Provider DNS Resolver 203.0.113.234

23 Technical flaws in DNS blocking

24 Technical flaws: multiple / changing domain names What’s the IP address for www.example.eu? www.example.eu www.ejemplo.eu Access Provider DNS Resolver

25 Technical flaws: multiple / changing domain names www.example.eu www.ejemplo.eu Access Provider DNS Resolver No such domain.

26 Technical flaws: multiple / changing domain names www.example.eu www.ejemplo.eu Access Provider DNS Resolver Ok, can I have IP address for www.ejemplo.eu?

27 Technical flaws: multiple / changing domain names www.example.eu www.ejemplo.eu Root Name Server Access Provider DNS Resolver

28 Technical flaws: multiple / changing domain names www.example.eu www.ejemplo.eu Access Provider DNS Resolver.eu Registry DNS server

29 Technical flaws: multiple / changing domain names www.example.eu www.ejemplo.eu Access Provider DNS Resolver DNS ejemplo.eu

30 Technical flaws: multiple / changing domain names www.example.eu www.ejemplo.eu Access Provider DNS Resolver The IP address for www.ejemplo.eu is: 192.0.2.12

31 Technical flaws: multiple / changing domain names www.example.eu www.ejemplo.eu Access Provider DNS Resolver

32 192.0.2.12 Technical flaws: user can bypass DNS by typing IP address directly into browser

33

34 Technical flaws: user can bypass DNS by typing IP directly into browser www.example.eu 192.0.2.12 Access Provider DNS Resolver

35 Technical flaws: many companies run their own DNS resolver Jones & Jones Ltd DNS Resolver Access Provider DNS Resolver What’s the IP address for www.example.eu?

36 Technical flaws: many companies run their own DNS resolver Jones & Jones Ltd Access Provider DNS Resolver Root Name Server DNS Resolver

37 Technical flaws: many companies run their own DNS resolver Jones & Jones Ltd Access Provider DNS Resolver.eu Registry DNS server DNS Resolver

38 Technical flaws: many companies run their own DNS resolver Jones & Jones Ltd DNS Resolver Access Provider DNS Resolver DNS example.eu

39 Technical flaws: many companies run their own DNS resolver Jones & Jones Ltd DNS Resolver Access Provider DNS Resolver The IP address for www.example.eu is: 192.0.2.12

40 Technical flaws: many companies run their own DNS resolver Jones & Jones Ltd DNS Resolver Access Provider DNS Resolver www.example.eu 192.0.2.12

41 Technical flaws: client can use a third-party DNS resolver Access Provider DNS Resolver

42 Technical flaws: client can use a third-party DNS resolver

43

44

45 Access Provider DNS Resolver Technical flaws: client can use a third-party DNS resolver 3 rd party DNS Resolver

46 Access Provider DNS Resolver Technical flaws: client can use a third-party DNS resolver What’s the IP address for www.example.eu? 3 rd party DNS Resolver

47 Technical flaws: client can use a third-party DNS resolver 3 rd party DNS Resolver Root Name Server Access Provider DNS Resolver

48 Technical flaws: client can use a third-party DNS resolver 3 rd party DNS Resolver.eu Registry DNS server Access Provider DNS Resolver

49 Technical flaws: client can use a third-party DNS resolver 3 rd party DNS Resolver DNS example.eu Access Provider DNS Resolver

50 Access Provider DNS Resolver Technical flaws: client can use a third-party DNS resolver 3 rd party DNS Resolver

51 Technical flaws: client can use a third-party DNS resolver www.example.eu 192.0.2.12 Access Provider DNS Resolver

52 Technical flaws: web proxies What’s the IP address for www.proxy.example ? Access Provider DNS Resolver

53 Technical flaws: web proxies Root Name Server Access Provider DNS Resolver

54 Technical flaws: web proxies.example Registry DNS server Access Provider DNS Resolver

55 Technical flaws: web proxies DNS proxy.example Access Provider DNS Resolver

56 Technical flaws: web proxies The IP address for www.proxy.example is 198.51.100.207 Access Provider DNS Resolver

57 Technical flaws: web proxies www.proxy.example 198.51.100.207 Access Provider DNS Resolver DNS Resolver

58 Technical flaws: web proxies Enter the URL you wish to access: www.example.eu

59 Technical flaws: web proxies www.proxy.example 198.51.100.207 Access Provider DNS Resolver DNS Resolver Where is www. example.eu ? Where is www. example.eu ?

60 Technical flaws: web proxies www.proxy.example 198.51.100.207 Access Provider DNS Resolver DNS Resolver Root Name Server

61 Technical flaws: web proxies www.proxy.example 198.51.100.207 Access Provider DNS Resolver DNS Resolver.eu Registry DNS server

62 Technical flaws: web proxies www.proxy.example 198.51.100.207 Access Provider DNS Resolver DNS Resolver DNS example.eu 192.0.2.12

63 Technical flaws: web proxies www.proxy.example 198.51.100.207 Access Provider DNS Resolver DNS Resolver www.example.eu

64 Technical flaws: web proxies Enter the URL you wish to access: www.example.eu

65 Other tools use the proxy principle

66 Conclusions “DNS blocking” is a technical term – It describes a technical procedure, not an outcome – It is not synonymous with “preventing access using DNS” – It is unlikely to prevent users from reaching content they are actively seeking There is a big difference between seeking to protect users from content they wish to avoid, and seeking to obstruct users from reaching content they seek – In the first case, you can enlist the support of users and the software and services they use – In the latter, there is always a way around any impediment, and these ways can and will be made easy for anyone to use

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