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Net::DNS(3)		       User Contributed Perl Documentation		      Net::DNS(3)

NAME
       Net::DNS - Perl interface to the Domain Name System

SYNOPSIS
	   use Net::DNS;

DESCRIPTION
       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
       "gethostbyname" and "gethostbyaddr".

       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.

   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:

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

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

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

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

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

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

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

   Question Objects
       Net::DNS::Question objects represent the question 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.

       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.

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

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

       Returns the version of Net::DNS.

   mx
	   # 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.

   yxrrset
       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 "Net::DNS::RR" object or "undef" if the object couldn't be created.

   nxrrset
       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 "Net::DNS::RR" object or "undef" if the object couldn't be created.

   yxdomain
       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 "Net::DNS::RR" object or "undef" if the object couldn't be created.

   nxdomain
       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 "Net::DNS::RR" object or "undef" if the object couldn't be created.

   rr_add
       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 "Net::DNS::RR" object or "undef" if the object couldn't be created.

   rr_del
       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 "Net::DNS::RR" object or "undef" if the object couldn't be created.

Zone Serial Number Management
       The Net::DNS module provides auxiliary functions which support policy-driven zone serial
       numbering regimes.

   Strictly Sequential
	   $successor = $soa->serial( SEQUENTIAL );

       The existing serial number is incremented modulo 2**32.

   Time Encoded
	   $successor = $soa->serial( UNIXTIME );

       The Unix time scale will be used as the basis for zone serial numbering. The serial number
       will be incremented if the time elapsed since the previous update is less than one second.

   Date Encoded
	   $successor = $soa->serial( YYYYMMDDxx );

       The 32 bit value returned by the auxiliary YYYYMMDDxx() function will be used as the base
       for the date-coded zone serial number.  Serial number increments must be limited to 100
       per day for the date information to remain useful.

   Sorting of RR arrays
       As of version 0.55 there is functionality to help you sort RR arrays. 'rrsort()' is the
       function that is available to do the sorting. In most cases rrsort will give you the
       answer that you want but you can specify your own sorting method by using the
       Net::DNS::RR::FOO->set_rrsort_func() class method. See Net::DNS::RR for details.

       rrsort()

	  use Net::DNS qw(rrsort);

	  my @prioritysorted=rrsort("SRV","priority",@rr_array);

       rrsort() selects all RRs from the input array that are of the type that are defined in the
       first argument. Those RRs are sorted based on the attribute that is specified as second
       argument.

       There are a number of RRs for which the sorting function is specifically defined for
       certain attributes.  If such sorting function is defined in the code (it can be set or
       overwritten using the set_rrsort_func() class method) that function is used.

       For instance:
	  my @prioritysorted=rrsort("SRV","priority",@rr_array); returns the SRV records sorted
       from lowest to heighest priority and for equal priorities from heighes to lowes weight.

       If the function does not exist then a numerical sort on the attribute value is performed.
	  my @portsorted=rrsort("SRV","port",@rr_array);

       If the attribute does not exist for a certain RR than the RRs are sorted on string
       comparrisson of the rdata.

       If the attribute is not defined than either the default_sort function will be defined or
       "Canonical sorting" (as defined by DNSSEC) will be used.

       rrsort() returns a sorted array with only elements of the specified RR type or undef.

       rrsort() returns undef when arguments are incorrect.

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

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

   Look up a host's addresses.
	 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";
	 }

   Find the nameservers for a domain.
	 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";
	 }

   Find the MX records for a domain.
	 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";
	 }

   Print a domain's SOA record in zone file format.
	 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";
	 }

   Perform a zone transfer and print all the records.
	 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;
	 }

   Perform a background query and do some other work while waiting for the answer.
	 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;

   Send a background query and use select to determine when the answer has arrived.
	 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";
	 }

BUGS
       "Net::DNS" is slow.

       For other items to be fixed, or if you discover a bug in this distribution please use the
       CPAN bug reporting system.

COPYRIGHT
       Copyright (c)1997-2002 Michael Fuhr.  Portions Copyright(c)2002-2004 Chris Reinhardt.
       Portions Copyright(c)2005 Olaf Kolkman (RIPE NCC) Portions Copyright(c)2006 Olaf Kolkman
       (NLnet Labs)

       All rights reserved.

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

AUTHOR INFORMATION
       Net::DNS is currently maintained at NLnet Labs (www.nlnetlabs.nl) 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 syndicate:
	   http://www.net-dns.org/blog/

SEE ALSO
       perl, 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

perl v5.16.3				    2012-12-28				      Net::DNS(3)
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