Net::DNS

Net::DNS is a DNS library written in pure Ruby. It started as a port of Perl Net::DNS module, but it evolved in time into a full Ruby library.

Features

  • Complete OO interface
  • Clean and intuitive API
  • Modular and flexible

Requirements

  • Ruby >= 1.8.7

Installation

The best way to install this library is via RubyGems.

$ gem install net-dns

You might need administrator privileges on your system to install the gem.

API Documentation

Visit the page http://rdoc.info/gems/net-dns

Trivial resolver

The simplest way to use the library is to invoke the Resolver() method:

require 'rubygems' 
require 'net/dns'
p Resolver("www.google.com")

The output is compatible with BIND zone files and it's the same you would get with the dig utility.

;; Answer received from localhost:53 (212 bytes)
;;
;; HEADER SECTION
;; id = 64075
;; qr = 1       opCode: QUERY   aa = 0  tc = 0  rd = 1
;; ra = 1       ad = 0  cd = 0  rcode = NoError
;; qdCount = 1  anCount = 3     nsCount = 4     arCount = 4

;; QUESTION SECTION (1 record):
;; google.com.                  IN      A

;; ANSWER SECTION (3 records):
google.com.             212     IN      A       74.125.45.100
google.com.             212     IN      A       74.125.67.100
google.com.             212     IN      A       209.85.171.100

;; AUTHORITY SECTION (4 records):
google.com.             345512  IN      NS      ns1.google.com.
google.com.             345512  IN      NS      ns4.google.com.
google.com.             345512  IN      NS      ns2.google.com.
google.com.             345512  IN      NS      ns3.google.com.

;; ADDITIONAL SECTION (4 records):
ns1.google.com.         170275  IN      A       216.239.32.10
ns2.google.com.         170275  IN      A       216.239.34.10
ns3.google.com.         170275  IN      A       216.239.36.10
ns4.google.com.         170275  IN      A       216.239.38.10

An optional block can be passed yielding the Net::DNS::Packet object

Resolver("www.google.com") { |packet| puts packet.size + " bytes" }
# => 484 bytes

Same for Net::DNS::Resolver.start():

Net::DNS::Resolver.start("google.com").answer.size
# => 5

As optional parameters, +TYPE+ and +CLASS+ can be specified.

p Net::DNS::Resolver.start("google.com", Net::DNS::MX)

;; Answer received from localhost:53 (316 bytes)
;;
;; HEADER SECTION
;; id = 59980
;; qr = 1       opCode: QUERY   aa = 0  tc = 0  rd = 1
;; ra = 1       ad = 0  cd = 0  rcode = NoError
;; qdCount = 1  anCount = 4     nsCount = 4     arCount = 8

;; QUESTION SECTION (1 record):
;; google.com.                  IN      MX

;; ANSWER SECTION (4 records):
google.com.             10800   IN      MX      10 smtp2.google.com.
google.com.             10800   IN      MX      10 smtp3.google.com.
google.com.             10800   IN      MX      10 smtp4.google.com.
google.com.             10800   IN      MX      10 smtp1.google.com.

Handling the response packet

The method Net::DNS::Resolver.start is a wrapper around Resolver.new. It returns a new Net::DNS::Packet object.

A DNS packet is divided into 5 sections:

  • header section # => a Net::DNS::Header object
  • question section # => a Net::DNS::Question object
  • answer section # => an Array of Net::DNS::RR objects
  • authority section # => an Array of Net::DNS::RR objects
  • additional section # => an Array of Net::DNS::RR objects

You can access each section by calling the attribute with the same name on a Packet object:

packet = Net::DNS::Resolver.start("google.com")

header = packet.header
answer = packet.answer

puts "The packet is #{packet.data.size} bytes"
puts "It contains #{header.anCount} answer entries"

answer.any? {|ans| p ans}

The output is

The packet is 378 bytes
It contains 3 answer entries
google.com.             244     IN      A       74.125.45.100
google.com.             244     IN      A       74.125.67.100
google.com.             244     IN      A       209.85.171.100

A better way to handle the answer section is to use the iterators directly on a Packet object:

packet.each_address do |ip|
  puts "#{ip} is alive" if Ping.pingecho(ip.to_s, 10, 80)
end

Gives:

74.125.45.100 is alive
74.125.67.100 is alive
209.85.171.100 is alive

License

Net::DNS is distributed under the same license Ruby is.

Authors

  • Marco Ceresa (@bluemonk)
  • Simone Carletti (@weppos)