Learning DNS in 10 years

From RubyConf Mini 2022

Transcript

8. notice when you're confused read the specification do experiments spy on it what's DNS? implement your own terrible version
14. notice when you're confused read the specification do experiments spy on it what's DNS? implement your own terrible version
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
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...
34. browser resolver authoritative nameservers DNS query DNS query where's new.jvns.ca? where's new.jvns.ca? NXDOMAIN NXDOMAIN
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.”
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
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!
54. require 'socket' sock = UDPSocket.new sock.bind('0.0.0.0', 0) sock.connect('8.8.8.8', 53)
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
68. notice when you're confused read the specification do experiments spy on it implement your own terrible version