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

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 familiar with the structure of a DNS packet.  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 may 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.  A packet object has five
       sections:

       o  header, represented by a Net::DNS::Header object

       o  question, a list of no more than one Net::DNS::Question object

       o  answer, a list of Net::DNS::RR objects

       o  authority, a list of Net::DNS::RR objects

       o  additional, a list of Net::DNS::RR objects

   Update Objects
       Net::DNS::Update is a subclass of Net::DNS::Packet useful for creating dynamic update
       requests.

   Header Object
       The Net::DNS::Header object mediates access to the header data which resides within the
       corresponding Net::DNS::Packet.

   Question Object
       The Net::DNS::Question object represents the content of the question section of the 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.

       Do not assume that RR objects will be of the type requested.  The type of an RR object
       must be checked before calling any methods.

METHODS
       Net::DNS exports methods and auxilliary functions to support DNS updates, zone serial
       number management, and simple DNS queries.

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

       Returns the version of Net::DNS.

   rr
           # Use a default resolver -- can not get an error string this way.
           use Net::DNS;
           my @rr = rr("example.com");
           my @rr = rr("example.com", "AAAA");
           my @rr = rr("example.com", "AAAA", "IN");

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

           my ($ptr) = rr("2001:DB8::dead:beef");

       The "rr()" method provides simple RR lookup for scenarios where the full flexibility of
       Net::DNS is not required.

       Returns a list of Net::DNS::RR objects for the specified name or an empty list if the
       query failed or no record was found.

       See "EXAMPLES" for more complete examples.

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

           # Use your own resolver object.
           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 record was found.

       This method does not look up address records; it resolves MX only.

Dynamic DNS Update Support
       The Net::DNS module provides auxilliary functions which support dynamic DNS update
       requests.

           $update = Net::DNS::Update->new( 'example.com' );

           $update->push( prereq => nxrrset('example.com. AAAA') );
           $update->push( update => rr_add('example.com. 86400 AAAA 2001::DB8::F00') );

   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 AAAA") );

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

           # RRset exists (value-dependent)
           $update->push( pre => yxrrset("host.example.com AAAA 2001:DB8::1") );

       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 could not be created.

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

           $update->push( pre => nxrrset("host.example.com AAAA") );

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

       Returns a Net::DNS::RR object or "undef" if the object could not be created.

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

           $update->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 could not be created.

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

           $update->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 could not be created.

   rr_add
       Use this method to add RRs to a zone.

           $update->push( update => rr_add("host.example.com AAAA 2001:DB8::c001:a1e") );

       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 could not be created.

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

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

       Meaning:  Delete all RRs having the specified name.

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

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

           # Delete a specific RR.
           $update->push( update => rr_del("host.example.com AAAA 2001:DB8::dead:beef") );

       Meaning:  Delete the RR which matches the specified argument.

       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 could not be created.

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

           $soa->serial(SEQUENTIAL);
           $soa->serial(YYYMMDDxx);

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

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

   UNIXTIME
           $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.

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

       The 32 bit value returned by the auxilliary "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
       "rrsort()" provides functionality to help you sort RR arrays. In most cases this will give
       you the result that you expect, 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;

           my @sorted = rrsort( $rrtype, $attribute, @rr_array );

       "rrsort()" selects all RRs from the input array that are of the type defined by 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 defined in the code.

       For instance:

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

       returns the SRV records sorted from lowest to highest priority and for equal priorities
       from highest to lowest 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 is not defined then either the "default_sort()" function or "canonical
       sorting" (as defined by DNSSEC) will be used.

       "rrsort()" returns a sorted array containing only elements of the specified RR type.  Any
       other RR types are silently discarded.

       "rrsort()" returns an empty list when arguments are incorrect.

EXAMPLES
       The following brief examples illustrate some of the features of Net::DNS.  The
       documentation for individual modules and the demo scripts included with the distribution
       provide more extensive examples.

       See Net::DNS::Update for an example of performing dynamic updates.

   Look up host addresses.
           use Net::DNS;
           my $res   = Net::DNS::Resolver->new;
           my $reply = $res->search("www.example.com", "AAAA");

           if ($reply) {
               foreach my $rr ($reply->answer) {
                   print $rr->address, "\n" if $rr->can("address");
               }
           } else {
               warn "query failed: ", $res->errorstring, "\n";
           }

   Find the nameservers for a domain.
           use Net::DNS;
           my $res   = Net::DNS::Resolver->new;
           my $reply = $res->query("example.com", "NS");

           if ($reply) {
               foreach $rr (grep { $_->type eq "NS" } $reply->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, "\t", $rr->exchange, "\n";
               }
           } else {
               warn "Can not find MX records for $name: ", $res->errorstring, "\n";
           }

   Print domain SOA record in zone file format.
           use Net::DNS;
           my $res   = Net::DNS::Resolver->new;
           my $reply = $res->query("example.com", "SOA");

           if ($reply) {
               foreach my $rr ($reply->answer) {
                   $rr->print;
               }
           } else {
               warn "query failed: ", $res->errorstring, "\n";
           }

   Perform a zone transfer and print all the records.
           use Net::DNS;
           my $res  = Net::DNS::Resolver->new;
           $res->tcp_timeout(20);
           $res->nameservers("ns.example.com");

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

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

           warn $res->errorstring if $res->errorstring;

   Perform a background query and print the reply.
           use Net::DNS;
           my $res    = Net::DNS::Resolver->new;
           $res->udp_timeout(10);
           $res->tcp_timeout(20);
           my $socket = $res->bgsend("host.example.com", "AAAA");

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

           my $packet = $res->bgread($socket);
           if ($packet) {
               $packet->print;
           } else {
               warn "query failed: ", $res->errorstring, "\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)1997-2000 Michael Fuhr.

       Portions Copyright (c)2002,2003 Chris Reinhardt.

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

       Portions Copyright (c)2006 Olaf Kolkman (NLnet Labs)

       Portions Copyright (c)2014 Dick Franks

       All rights reserved.

LICENSE
       Permission to use, copy, modify, and distribute this software and its documentation for
       any purpose and without fee is hereby granted, provided that the original copyright
       notices appear in all copies and that both copyright notice and this permission notice
       appear in supporting documentation, and that the name of the author not be used in
       advertising or publicity pertaining to distribution of the software without specific prior
       written permission.

       THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
       INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
       PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE
       FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
       OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
       DEALINGS IN THE SOFTWARE.

AUTHOR INFORMATION
       Net::DNS is maintained at NLnet Labs (www.nlnetlabs.nl) by Willem Toorop.

       Between 2005 and 2012 Net::DNS was maintained by Olaf Kolkman.

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

       Net::DNS was created in 1997 by Michael Fuhr.

SEE ALSO
       perl, Net::DNS::Resolver, Net::DNS::Question, Net::DNS::RR, Net::DNS::Packet,
       Net::DNS::Update, RFC1035, <http://www.net-dns.org/>, DNS and BIND by Paul Albitz &
       Cricket Liu

perl v5.32.1                                2021-12-18                              Net::DNS(3pm)

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