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

NAME

       Net::DNS - Perl interface to the DNS resolver

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.

       The "Net::DNS::Update" package is a front-end to "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, "
";

       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-depen-
       dent:

	   # RRset exists (value-independent)
	   $packet->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.

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, "
";
	     }
	 }
	 else {
	     print "query failed: ", $res->errorstring, "
";
	 }

       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 $rr ($query->answer) {
		 next unless $rr->type eq "NS";
		 print $rr->nsdname, "
";
	     }
	 }
	 else {
	     print "query failed: ", $res->errorstring, "
";
	 }

       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, "
";
	     }
	 }
	 else {
	     print "can't find MX records for $name: ", $res->errorstring, "
";
	 }

       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, "
";
	 }

       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 {
	     print "timed out after $timeout seconds
";
	 }

BUGS

       "Net::DNS" is slow.  Real slow.

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

COPYRIGHT

       Copyright (c) 1997-2002 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.

AUTHOR INFORMATION

       Net::DNS is currently maintained by a group, led by:	 Chris Reinhardt      ctriv@net-dns.org

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

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

SEE ALSO

       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

perl v5.8.0							    2002-11-17							       Net::DNS(3)