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Learning DNS in 10 years

Avatar for Julia Evans Julia Evans
February 01, 2023
Technology
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Learning DNS in 10 years

From RubyConf Mini 2022

Avatar for Julia Evans

Julia Evans

February 01, 2023
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Transcript

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  8. notice when you're confused read the specification do experiments spy

    on it what's DNS? implement your own terrible version
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  14. notice when you're confused read the specification do experiments spy

    on it what's DNS? implement your own terrible version
  15. None
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  17. $ dig example.com example.com. 86400 IN A 93.184.216.34

  18. $ dig example.com example.com. 86400 IN A 93.184.216.34

  19. +noall +answer .digrc

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  25. browser resolver authoritative nameservers DNS query DNS query where's example.com?

    where's example.com? 93.184.216.34! 93.184.216.34!

  26. resolver browser what's the IP for example.com? hmm, I'll look

    in my cache...
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  34. browser resolver authoritative nameservers DNS query DNS query where's new.jvns.ca?

    where's new.jvns.ca? NXDOMAIN NXDOMAIN
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  38. “The TTL of this record is set from the minimum

    of the MINIMUM field of the SOA record and the TTL of the SOA itself, and indicates how long a resolver may cache the negative answer.”
  39. None

  40. $ dig +all new.jvns.ca ;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN,

    id: 23308 [redacted] ;; AUTHORITY SECTION: jvns.ca. 10800 IN SOA ns1.gandi.net. hostmaster.gandi.net. 1662903879 10800 3600 604800 10800
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  49. browser resolver authoritative nameservers DNS query DNS query where's example.com?

    where's example.com? 93.184.216.34! 93.184.216.34!
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  54. require 'socket' sock = UDPSocket.new sock.bind('0.0.0.0', 0) sock.connect('8.8.8.8', 53)

  55. None

  56. hex_string = "b9620100000100..." bytes = [hex_string].pack('H*') sock.send(bytes, 0)

  57. b96201000001000000000000 076578616d706c6503636f6d0000010001

  58. b96201000001000000000000 076578616d706c6503636f6d0000010001

  59. b96201000001000000000000

  60. def make_question_header(query_id) # id, flags, num questions, num answers, ...

    [query_id, 0x0100, 0x0001, 0x0000, 0x0000, 0x0000] .pack('nnnnnn') end

  61. b96201000001000000000000 076578616d706c6503636f6d0000010001

  62. 076578616d706c6503636f6d0000010001 7 e x a m p l e 3

    c o m 0 1 1

  63. def encode_domain_name(domain) domain.split('.') .map { |x| x.length.chr + x }

    .join + "\0" end example.com 7example3com0

  64. def make_dns_query(domain, type) query_id = rand(65535) header = make_question_header(query_id) question

    = encode_domain_name(domain) + [type, 1].pack('nn') header + question end
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  68. notice when you're confused read the specification do experiments spy

    on it implement your own terrible version
  69. None