Class: PacketGen::Header::DNS

Inherits:
Base show all
Defined in:
lib/packetgen/header/dns.rb,
lib/packetgen/header/dns.rb,
lib/packetgen/header/dns/rr.rb,
lib/packetgen/header/dns/opt.rb,
lib/packetgen/header/dns/name.rb,
lib/packetgen/header/dns/option.rb,
lib/packetgen/header/dns/question.rb,
lib/packetgen/header/dns/qdsection.rb,
lib/packetgen/header/dns/rrsection.rb

Overview

DNS: Domain Name Service

A DNS packet consists of a header:

                                1  1  1  1  1  1
  0  1  2  3  4  5  6  7  8  9  0  1  2  3  4  5
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
|                      ID                       |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
|QR|   Opcode  |AA|TC|RD|RA|   Z    |   RCODE   |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
|                    QDCOUNT                    |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
|                    ANCOUNT                    |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
|                    NSCOUNT                    |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
|                    ARCOUNT                    |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

A DNS packet also contains up to 4 sections:

  • #qd, question section,

  • #an, answer section,

  • #ns, authoritary section,

  • #ar, additional information section.

Create a DNS header

# standalone
dns = PacketGen::Header::DNS.new
# in a IP packet
pkt = PacketGen.gen('IP').add('DNS')
# access to DNS header
pkt.dns   # => PacketGen::Header::DNS

DNS attributes

dns.id = 0x1234
dns.qr = false
dns.opcode = 0xe
dns.opcode = 'query'
dns.aa = dns.tc = dns.rd = dns.ra = false
dns.rcode = 0xa
dns.rcode = 'refused'
dns.qdcount = 123
dns.ancount = 0x1234
dns.nscount = 1
dns.arcount = 0

One can also access to DNS sections:

dns.qd   # => PacketGen::Header::DNS::QDSection
dns.an   # => PacketGen::Header::DNS::RRSection
dns.ns   # => PacketGen::Header::DNS::RRSection
dns.ar   # => PacketGen::Header::DNS::RRSection

Add a question to DNS question section

Adding a Question with QDSection#<< automagically increments #qdcount. To not modify qdcount, use QDSection#push.

# add a question about example.net IP address. Increment qdcount
dns.qd << PacketGen::Header::DNS::Question.new(dns, name: 'example.net')
# or
dns.qd << { rtype: 'Question', name: 'example.net' }
# add a question about example.net IPv6 address. Dot not modify qdcount
dns.qd.push PacketGen::Header::DNS::Question.new(dns, name: 'example.net', type: 'AAAA')
# or
dns.qd.push({ rtype: 'Question', name: 'example.net', type: 'AAAA' })

Add a ressource record to a DNS section

Adding a RR with Types::Array#<< automagically increments section counter. To not modify it, use Types::Array#push

# add a RR to answer section. Increment ancount
dns.an << PacketGen::Header::DNS::RR.new(dns, name: 'example.net', rdata: IPAddr.new('1.2.3.4').hton)
# or
dns.an << { rtype: 'RR', name: 'example.net', rdata: IPAddr.new('1.2.3.4').hton }
# add a RR to NS section. Dot not modify nscount
rdata = PacketGen::Header::DNS::Name.new(dns).parse('dns.net')
dns.ns.push PacketGen::Header::DNS::RR.new(dns, name: 'example.net', type: 'NS', rdata: rdata)
# or
dns.ns.push(rtype: 'RR', name: 'example.net', type: 'NS', rdata: rdata)

Extended DNS EDNS(0)

# Add an OPT to ar section
dns.ar << PacketGen::Header::DNS::OPT.new(dns, udp_size: 4096, ext_rcode: 43)
# or
dns.ar << { rtype: 'OPT', udp_size: 4096, ext_rcode: 43 }
# add an option to OPT record
dns.ar.last.options << PacketGen::Header::DNS::Option.new(code: 48, length: 2, data: "12")

Author:

  • Sylvain Daubert

Defined Under Namespace

Classes: Name, OPT, Option, QDSection, Question, RR, RRSection

Constant Summary collapse

UDP_PORT =

Port number for DNS over UDP

53
TCP_PORT =

Port number for DNS over TCP

UDP_PORT
OPCODES =

DNS opcodes

{
  'query'  => 0,
  'iquery' => 1,
  'status' => 2,
  'notify' => 4,
  'update' => 5
}
RCODES =

DNS Response codes

{
  'ok'              => 0,
  'no-error'        => 0,
  'format-error'    => 1,
  'server-failure'  => 2,
  'name-error'      => 3,
  'not-implemented' => 4,
  'refused'         => 5
}

Instance Attribute Summary collapse

Attributes inherited from Base

#packet

Instance Method Summary collapse

Methods inherited from Base

bind_header, #header_id, inherited, #ip_header, known_headers, #parse?, #protocol_name

Methods inherited from Types::Fields

#[], #[]=, #body=, define_bit_fields_on, define_field, define_field_after, define_field_before, #fields, #force_binary, inherited, #initialize, #sz, #to_h, #to_s

Constructor Details

This class inherits a constructor from PacketGen::Types::Fields

Instance Attribute Details

#aa ⇒ Boolean

Returns Authoritative answer.

Returns:

  • (Boolean) —

    Authoritative answer



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# File 'lib/packetgen/header/dns.rb', line 176

define_bit_fields_on :u16, :qr, :opcode, 4, :aa, :tc, :rd, :ra, :z,
:ad, :cd, :rcode, 4

#ad ⇒ Boolean

Returns Authentic Data.

Returns:

  • (Boolean) —

    Authentic Data



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# File 'lib/packetgen/header/dns.rb', line 176

define_bit_fields_on :u16, :qr, :opcode, 4, :aa, :tc, :rd, :ra, :z,
:ad, :cd, :rcode, 4

#an ⇒ RRSection

Returns:



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# File 'lib/packetgen/header/dns.rb', line 150

define_field :an, RRSection, builder: ->(dns) { RRSection.new(dns, dns[:ancount]) }

#ancount ⇒ Integer

Returns:

  • (Integer) 


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# File 'lib/packetgen/header/dns.rb', line 138

define_field :ancount, Types::Int16

#ar ⇒ RRSection

Returns:



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# File 'lib/packetgen/header/dns.rb', line 156

define_field :ar, RRSection, builder: ->(dns) { RRSection.new(dns, dns[:arcount]) }

#arcount ⇒ Integer

Returns:

  • (Integer) 


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# File 'lib/packetgen/header/dns.rb', line 144

define_field :arcount, Types::Int16

#cd ⇒ Boolean

Returns Checking Disabled.

Returns:

  • (Boolean) —

    Checking Disabled



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# File 'lib/packetgen/header/dns.rb', line 176

define_bit_fields_on :u16, :qr, :opcode, 4, :aa, :tc, :rd, :ra, :z,
:ad, :cd, :rcode, 4

#id ⇒ Integer

Returns:

  • (Integer) 


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# File 'lib/packetgen/header/dns.rb', line 129

define_field :id, Types::Int16

#ns ⇒ RRSection

Returns:



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# File 'lib/packetgen/header/dns.rb', line 153

define_field :ns, RRSection, builder: ->(dns) { RRSection.new(dns, dns[:nscount]) }

#nscount ⇒ Integer

Returns:

  • (Integer) 


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# File 'lib/packetgen/header/dns.rb', line 141

define_field :nscount, Types::Int16

#opcode ⇒ Integer

Returns Kind of query. See OPCODES.

Returns:

  • (Integer) —

    Kind of query. See OPCODES.



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# File 'lib/packetgen/header/dns.rb', line 176

define_bit_fields_on :u16, :qr, :opcode, 4, :aa, :tc, :rd, :ra, :z,
:ad, :cd, :rcode, 4

#qd ⇒ QDSection

Returns:



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# File 'lib/packetgen/header/dns.rb', line 147

define_field :qd, QDSection, builder: ->(dns) { QDSection.new(dns, dns[:qdcount]) }

#qdcount ⇒ Integer

Returns:

  • (Integer) 


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# File 'lib/packetgen/header/dns.rb', line 135

define_field :qdcount, Types::Int16

#qr ⇒ Boolean

Returns query (false) or response (true).

Returns:

  • (Boolean) —

    query (false) or response (true)



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# File 'lib/packetgen/header/dns.rb', line 176

define_bit_fields_on :u16, :qr, :opcode, 4, :aa, :tc, :rd, :ra, :z,
:ad, :cd, :rcode, 4

#ra ⇒ Boolean

Returns Recursion Available.

Returns:

  • (Boolean) —

    Recursion Available



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# File 'lib/packetgen/header/dns.rb', line 176

define_bit_fields_on :u16, :qr, :opcode, 4, :aa, :tc, :rd, :ra, :z,
:ad, :cd, :rcode, 4

#rcode ⇒ Integer

Returns Response code. See RCODES.

Returns:

  • (Integer) —

    Response code. See RCODES.



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# File 'lib/packetgen/header/dns.rb', line 176

define_bit_fields_on :u16, :qr, :opcode, 4, :aa, :tc, :rd, :ra, :z,
:ad, :cd, :rcode, 4

#rd ⇒ Boolean

Returns Recursion Desired.

Returns:

  • (Boolean) —

    Recursion Desired



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# File 'lib/packetgen/header/dns.rb', line 176

define_bit_fields_on :u16, :qr, :opcode, 4, :aa, :tc, :rd, :ra, :z,
:ad, :cd, :rcode, 4

#tc ⇒ Boolean

Returns Truncation.

Returns:

  • (Boolean) —

    Truncation



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# File 'lib/packetgen/header/dns.rb', line 176

define_bit_fields_on :u16, :qr, :opcode, 4, :aa, :tc, :rd, :ra, :z,
:ad, :cd, :rcode, 4

#u16 ⇒ Integer

Returns:

  • (Integer) 


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# File 'lib/packetgen/header/dns.rb', line 132

define_field :u16, Types::Int16

Instance Method Details

#inspect ⇒ String

Returns:

  • (String) 


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# File 'lib/packetgen/header/dns.rb', line 244

def inspect
  str = Inspect.dashed_line(self.class, 2)
  to_h.each do |attr, value|
    if attr == :u16
      flags = [:qr, :aa, :tc, :rd, :ra].select! { |attr| send "#{attr}?" }.
              map(&:to_s).join(',')
      str << Inspect.shift_level(2)
      str << Inspect::INSPECT_FMT_ATTR % ['Flags', 'flags', flags]
      opcode = '%-10s (%u)' % [OPCODES.key(self.opcode), self.opcode]
      str << Inspect.shift_level(2)
      str << Inspect::INSPECT_FMT_ATTR % ['Integer', 'opcode', opcode]
      rcode = '%-10s (%u)' % [RCODES.key(self.rcode), self.rcode]
      str << Inspect.shift_level(2)
      str << Inspect::INSPECT_FMT_ATTR % ['Integer', 'rcode', rcode]
    else
      str << Inspect.inspect_attribute(attr, value, 2)
    end
  end
  str
end

#query? ⇒ Boolean

Is message a query

Returns:

  • (Boolean) 


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# File 'lib/packetgen/header/dns.rb', line 239

def query?
  !qr?
end

#read(str) ⇒ self

Read DNS header and sections from a string

Parameters:

  • str (String) —

    binary string

Returns:

  • (self) 


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# File 'lib/packetgen/header/dns.rb', line 182

def read(str)
  return self if str.nil?
  force_binary str
  self[:id].read str[0, 2]
  self[:u16].read str[2, 2]
  self[:qdcount].read str[4, 2]
  self[:ancount].read str[6, 2]
  self[:nscount].read str[8, 2]
  self[:arcount].read str[10, 2]
  self[:qd].read str[12..-1] if self.qdcount > 0
  start = 12 + self[:qd].sz
  self[:an].read str[start..-1] if self.ancount > 0
  start += self[:an].sz
  self[:ns].read str[start..-1] if self.nscount > 0
  start += self[:ns].sz
  self[:ar].read str[start..-1] if self.arcount > 0
  self
end

#response? ⇒ Boolean

Is message a response

Returns:

  • (Boolean) 


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# File 'lib/packetgen/header/dns.rb', line 233

def response?
  qr?
end