Net::DNS - Perl interface to the DNS resolver

CWuse Net::DNS;

Net::DNS is a collection of Perl modules that act as a Domain Name System (DNS) resolver. It allows the programmer to perform DNS queries that are beyond the capabilities of CWgethostbyname and CWgethostbyaddr.

The programmer should be somewhat familiar with the format of a DNS packet and its various sections. See RFC 1035 or DNS and BIND (Albitz & Liu) for details.

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.

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.

The Net::DNS::Update package is a subclass of Net::DNS::Packet for creating packet objects to be used in dynamic updates.

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

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

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

Don't assume that RR objects will be of the type you requested always check an RR object's type before calling any of its methods.

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

    print Net::DNS->version, "\n";

Returns the version of Net::DNS.

    # Use a default resolver -- can't get an error string this way.
    use Net::DNS;
    my @mx = mx("example.com");

    # Use your own resolver object.
    use Net::DNS;
    my $res = Net::DNS::Resolver->new;
    my  @mx = mx($res, "example.com");

Returns a list of Net::DNS::RR::MX objects representing the MX records for the specified name; the list will be sorted by preference. Returns an empty list if the query failed or no MX records were found.

This method does not look up A records it only performs MX queries.

See EXAMPLES for a more complete example.

Use this method to add an RRset exists prerequisite to a dynamic update packet. There are two forms, value-independent and value-dependent:

    # RRset exists (value-independent)
    $update->push(pre => yxrrset("host.example.com A"));

Meaning: At least one RR with the specified name and type must exist.

    # RRset exists (value-dependent)
    $packet->push(pre => yxrrset("host.example.com A 10.1.2.3"));

Meaning: At least one RR with the specified name and type must exist and must have matching data.

Returns a CWNet::DNS::RR object or CWundef if the object couldn't be created.

Use this method to add an RRset does not exist prerequisite to a dynamic update packet.

    $packet->push(pre => nxrrset("host.example.com A"));

Meaning: No RRs with the specified name and type can exist.

Returns a CWNet::DNS::RR object or CWundef if the object couldn't be created.

Use this method to add a name is in use prerequisite to a dynamic update packet.

    $packet->push(pre => yxdomain("host.example.com"));

Meaning: At least one RR with the specified name must exist.

Returns a CWNet::DNS::RR object or CWundef if the object couldn't be created.

Use this method to add a name is not in use prerequisite to a dynamic update packet.

    $packet->push(pre => nxdomain("host.example.com"));

Meaning: No RR with the specified name can exist.

Returns a CWNet::DNS::RR object or CWundef if the object couldn't be created.

Use this method to add RRs to a zone.

    $packet->push(update => rr_add("host.example.com A 10.1.2.3"));

Meaning: Add this RR to the zone.

RR objects created by this method should be added to the update section of a dynamic update packet. The TTL defaults to 86400 seconds (24 hours) if not specified.

Returns a CWNet::DNS::RR object or CWundef if the object couldn't be created.

Use this method to delete RRs from a zone. There are three forms: delete an RRset, delete all RRsets, and delete an RR.

    # Delete an RRset.
    $packet->push(update => rr_del("host.example.com A"));

Meaning: Delete all RRs having the specified name and type.

    # Delete all RRsets.
    $packet->push(update => rr_del("host.example.com"));

Meaning: Delete all RRs having the specified name.

    # Delete an RR.
    $packet->push(update => rr_del("host.example.com A 10.1.2.3"));

Meaning: Delete all RRs having the specified name, type, and data.

RR objects created by this method should be added to the update section of a dynamic update packet.

Returns a CWNet::DNS::RR object or CWundef if the object couldn't be created.

The following examples show how to use the CWNet::DNS modules. See the other manual pages and the demo scripts included with the source code for additional examples.

See the CWNet::DNS::Update manual page for an example of performing dynamic updates.

  use Net::DNS;
  my $res   = Net::DNS::Resolver->new;
  my $query = $res->search("host.example.com");

  if ($query) {
      foreach my $rr ($query->answer) {
          next unless $rr->type eq "A";
          print $rr->address, "\n";
      }
  } else {
      warn "query failed: ", $res->errorstring, "\n";
  }

  use Net::DNS;
  my $res   = Net::DNS::Resolver->new;
  my $query = $res->query("example.com", "NS");

  if ($query) {
      foreach $rr (grep { $_->type eq 'NS' } $query->answer) {
          print $rr->nsdname, "\n";
      }
  }
  else {
      warn "query failed: ", $res->errorstring, "\n";
  }

  use Net::DNS;
  my $name = "example.com";
  my $res  = Net::DNS::Resolver->new;
  my @mx   = mx($res, $name);

  if (@mx) {
      foreach $rr (@mx) {
          print $rr->preference, " ", $rr->exchange, "\n";
      }
  } else {
      warn "Can't find MX records for $name: ", $res->errorstring, "\n";
  }

  use Net::DNS;
  my $res   = Net::DNS::Resolver->new;
  my $query = $res->query("example.com", "SOA");

  if ($query) {
      ($query->answer)[0]->print;
  } else {
      print "query failed: ", $res->errorstring, "\n";
  }

  use Net::DNS;
  my $res  = Net::DNS::Resolver->new;
  $res->nameservers("ns.example.com");

  my @zone = $res->axfr("example.com");

  foreach $rr (@zone) {
      $rr->print;
  }

  use Net::DNS;
  my $res    = Net::DNS::Resolver->new;
  my $socket = $res->bgsend("host.example.com");

  until ($res->bgisready($socket)) {
      # do some work here while waiting for the answer
      # ...and some more here
  }

  my $packet = $res->bgread($socket);
  $packet->print;

  use Net::DNS;
  use IO::Select;

  my $timeout = 5;
  my $res     = Net::DNS::Resolver->new;
  my $bgsock  = $res->bgsend("host.example.com");
  my $sel     = IO::Select->new($bgsock);

  # Add more sockets to $sel if desired.
  my @ready = $sel->can_read($timeout);
  if (@ready) {
      foreach my $sock (@ready) {
          if ($sock == $bgsock) {
              my $packet = $res->bgread($bgsock);
              $packet->print;
              $bgsock = undef;
          }
          # Check for the other sockets.
          $sel->remove($sock);
          $sock = undef;
      }
  } else {
      warn "timed out after $timeout seconds\n";
  }

CWNet::DNS is slow.

For other items to be fixed, please see the TODO file included with the source distribution.

Copyright (c) 1997-2002 Michael Fuhr.

Portions Copyright (c) 2002-2004 Chris Reinhardt.

Portions Copyright (c) 2005 Olaf Kolkman (RIPE NCC)

All rights reserved. This program is free software; you may redistribute it and/or modify it under the same terms as Perl itself.

Net::DNS is currently maintained by: Olaf Kolkman olaf@net-dns.org

Between 2002 and 2004 Net::DNS was maintained by: Chris Reinhardt

Net::DNS was created by: Michael Fuhr mike@fuhr.org

For more information see: http://www.net-dns.org/

Stay tuned and syncicate: http://www.net-dns.org/blog/

perl(1), Net::DNS::Resolver, Net::DNS::Packet, Net::DNS::Update, Net::DNS::Header, Net::DNS::Question, Net::DNS::RR, RFC 1035, DNS and BIND by Paul Albitz & Cricket Liu