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. RReessoollvveerr OObbjjeeccttssA 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. PPaacckkeett OObbjjeeccttssNet::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.
UUppddaattee OObbjjeeccttssThe Net::DNS::Update package is a subclass of Net::DNS::Packet for
creating packet objects to be used in dynamic updates. HHeeaaddeerr OObbjjeeccttssNet::DNS::Header objects represent the header section of a DNS packet.
QQuueessttiioonn OObbjjeeccttssNet::DNS::Question objects represent the question section of a DNS
packet. RRRR OObbjjeeccttssNet::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. MMEETTHHOODDSSSee the manual pages listed above for other class-specific methods.
vveerrssiioonnprint Net::DNS->version, "\n";
Returns the version of Net::DNS.
mmxx# 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.
yyxxrrrrsseett Use this method to add an "RRset exists" prerequisite to a dynamicupdate 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)
$packet->push(pre => yxrrset("host.example.com A 10.1.2.3"));
Meaning: At least one RR with the specified name and type must exist and must have matching data.Returns a "Net::DNS::RR" object or "undef" if the object couldn't be
created. nnxxrrrrsseett Use this method to add an "RRset does not exist" prerequisite to a dynamic update packet.$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. yyxxddoommaaiinn Use this method to add a "name is in use" prerequisite to a dynamic update packet.$packet->push(pre => yxdomain("host.example.com"));
Meaning: At least one RR with the specified name must exist.Returns a "Net::DNS::RR" object or "undef" if the object couldn't be
created. nnxxddoommaaiinn Use this method to add a "name is not in use" prerequisite to a dynamic update packet.$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. rrrraadddd Use this method to add RRs to a zone.$packet->push(update => rradd("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. rrrrddeell 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 => rrdel("host.example.com A"));
Meaning: Delete all RRs having the specified name and type.# Delete all RRsets.
$packet->push(update => rrdel("host.example.com"));
Meaning: Delete all RRs having the specified name.# Delete an RR.
$packet->push(update => rrdel("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. SSoorrttiinngg ooff RRRR aarrrraayyss 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 theNet::DNS::RR::FOO->setrrsortfunc() class method. See Net::DNS::RR for
details. rrsort()use Net::DNS qw(rrsort);
my @prioritysorted=rrsort("SRV","priority",@rrarray); 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 setrrsortfunc() class method) that function is used. For instance: my @prioritysorted=rrsort("SRV","priority",@rrarray); 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",@rrarray); 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 defaultsort 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. EEXXAAMMPPLLEESSThe 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. LLooookk uupp aa hhoosstt''ss aaddddrreesssseess..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";
} FFiinndd tthhee nnaammeesseerrvveerrss ffoorr aa ddoommaaiinn..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";
} FFiinndd tthhee MMXX rreeccoorrddss ffoorr aa ddoommaaiinn..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";
} PPrriinntt aa ddoommaaiinn''ss SSOOAA rreeccoorrdd iinn zzoonnee ffiillee ffoorrmmaatt..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";
} PPeerrffoorrmm aa zzoonnee ttrraannssffeerr aanndd pprriinntt aallll tthhee rreeccoorrddss..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;
} PPeerrffoorrmm aa bbaacckkggrroouunndd qquueerryy aanndd ddoo ssoommee ootthheerr wwoorrkk wwhhiillee wwaaiittiinngg ffoorr tthhee aannsswweerr..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;
SSeenndd aa bbaacckkggrroouunndd qquueerryy aanndd uussee sseelleecctt ttoo ddeetteerrmmiinnee wwhheenn tthhee aannsswweerr hhaass aarrrriivveedd..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 = $sel->canread($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, please see the TODO file included with the source distribution. COPYRIGHTCopyright (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 INFORMATIONNet::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 ReinhardtNet::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/
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 Liuperl v5.8.8 2007-06-21 Net::DNS(3)