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Michael Fuhr

NAME

Net::DNS - Perl interface to the DNS resolver

SYNOPSIS

use Net::DNS;

DESCRIPTION

Net::DNS is a collection of Perl modules to interface with the Domain Name System (DNS) resolver. It allows the programmer to perform queries that are beyond the capabilities of gethostbyname and gethostbyaddr.

Resolver Objects

A resolver object is an instance of the Net::DNS::Resolver class. A program can have multiple resolver objects, each maintaining its own state information such as the nameservers to be queried, whether recursion is desired, etc.

Packet Objects

Net::DNS::Resolver queries return Net::DNS::Packet objects. Packet objects have five sections:

  • The header section, a Net::DNS::Header object.

  • The question section, a list of Net::DNS::Question objects.

  • The answer section, a list of Net::DNS::RR objects.

  • The authority section, a list of Net::DNS::RR objects.

  • The additional section, a list of Net::DNS::RR objects.

Header Objects

Net::DNS::Header objects represent the header section of a DNS packet.

Question Objects

Net::DNS::Question objects represent the query section of a DNS packet.

RR Objects

Net::DNS::RR is the base class for DNS resource record (RR) objects in the answer, authority, and additional sections of a DNS packet.

METHODS

version

    print Net::DNS->version;

Returns the version of Net::DNS.

See the manual pages listed above for class-specific methods.

EXAMPLES

The following examples show how to use the DNS modules. Please note that most of the examples are simple and expect a successful query and certain record types. See the demo scripts included with the source code for examples of more robust code.

  #
  # Look up a host's addresses.
  #
  use Net::DNS;
  $res = new Net::DNS::Resolver;
  $query = $res->search("foo.bar.com");
  foreach $record ($query->answer) {
      print $record->address, "\n";
  }

  #
  # Find the nameservers for a domain.
  #
  use Net::DNS;
  $res = new Net::DNS::Resolver;
  $query = $res->query("foo.com", "NS");
  foreach $nameserver ($query->answer) {
      print $nameserver->nsdname, "\n";
  }

  #
  # Find the MX records for a domain.
  #
  use Net::DNS;
  $res = new Net::DNS::Resolver;
  $query = $res->query("foo.com", "MX");
  foreach $mxhost ($query->answer) {
      print $mxhost->preference, " ", $mxhost->exchange, "\n";
  }

  #
  # Print a domain's SOA record in zone file format.
  #
  use Net::DNS;
  $res = new Net::DNS::Resolver;
  $query = $res->query("foo.com", "SOA");
  ($query->answer)[0]->print;

  #
  # Perform a zone transfer and print all the records.
  #
  use Net::DNS;
  $res = new Net::DNS::Resolver;
  $res->nameservers("ns.foo.com");
  @zone = $res->axfr("foo.com");
  foreach $rr (@zone) {
      $rr->print;
  }

  #
  # Send a background query and do some other processing while
  # waiting for the answer.
  #
  use Net::DNS;
  $res = new Net::DNS::Resolver;
  $socket = $res->bgsend("foo.bar.com");
  until ($res->bgisready($socket)) {
      # do some work here
      # ...and some more here
  }
  $packet = $res->bgread($socket);
  $packet->print;

  #
  # Send a background query and use select() to determine when the answer
  # has arrived.
  #
  use Net::DNS;
  $res = new Net::DNS::Resolver;
  $socket = $res->bgsend("foo.bar.com");
  $rin = "";
  vec($rin, $socket->fileno, 1) = 1;
  # Add more descriptors to $rin if desired.
  $timeout = 5;
  $nfound = select($rout=$rin, undef, undef, $timeout);
  if ($nfound < 1) {
      print "timed out after $timeout seconds\n";
  }
  elsif (vec($rout, $socket->fileno, 1) == 1) {
      $packet = $res->bgread($socket);
      $packet->print;
  }
  else {
      # Check for the other descriptors.
  }

COPYRIGHT

Copyright (c) 1997 Michael Fuhr. All rights reserved. This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

SEE ALSO

perl(1), Net::DNS::Resolver, Net::DNS::Packet, Net::DNS::Header, Net::DNS::Question, Net::DNS::RR, RFC 1035