Net::DNS(3pm)

1Net::DNS(3)           User Contributed Perl Documentation          Net::DNS(3)
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3
4

NAME

6       Net::DNS - Perl Interface to the Domain Name System
7

SYNOPSIS

9           use Net::DNS;
10

DESCRIPTION

12       Net::DNS is a collection of Perl modules that act as a Domain Name
13       System (DNS) resolver. It allows the programmer to perform DNS queries
14       that are beyond the capabilities of "gethostbyname" and
15       "gethostbyaddr".
16
17       The programmer should be somewhat familiar with the format of a DNS
18       packet and its various sections. See RFC 1035 or DNS and BIND (Albitz &
19       Liu) for details.
20
21   Resolver Objects
22       A resolver object is an instance of the Net::DNS::Resolver class.  A
23       program can have multiple resolver objects, each maintaining its own
24       state information such as the nameservers to be queried, whether
25       recursion is desired, etc.
26
27   Packet Objects
28       Net::DNS::Resolver queries return Net::DNS::Packet objects.  Packet
29       objects have five sections:
30
31       ·  The header section, a Net::DNS::Header object.
32
33       ·  The question section, a list of Net::DNS::Question objects.
34
35       ·  The answer section, a list of Net::DNS::RR objects.
36
37       ·  The authority section, a list of Net::DNS::RR objects.
38
39       ·  The additional section, a list of Net::DNS::RR objects.
40
41   Update Objects
42       Net::DNS::Update is a subclass of Net::DNS::Packet used to create
43       dynamic update requests.
44
45   Header Objects
46       Net::DNS::Header objects represent the header section of a DNS packet.
47
48   Question Objects
49       Net::DNS::Question objects represent the content of the question
50       section of a DNS packet.
51
52   RR Objects
53       Net::DNS::RR is the base class for DNS resource record (RR) objects in
54       the answer, authority, and additional sections of a DNS packet.
55
56       Do not assume that RR objects will be of the type requested.  The type
57       of an RR object must be checked before calling any methods.
58

METHODS

60       See the manual pages listed above for other class-specific methods.
61
62   version
63           print Net::DNS->version, "\n";
64
65       Returns the version of Net::DNS.
66
67   rr
68           # Use a default resolver -- can not get an error string this way.
69           use Net::DNS;
70           my @rr = rr("example.com");
71           my @rr = rr("example.com", "A");
72           my @rr = rr("example.com", "A", "IN");
73
74           # Use your own resolver object.
75           my $res = Net::DNS::Resolver->new;
76           my @rr  = rr($res, "example.com" ... );
77
78           my ($ptr) = rr("192.0.2.1");
79
80       The "rr()" method provides simple RR lookup for scenarios where the
81       full flexibility of Net::DNS is not required.
82
83       Returns a list of Net::DNS::RR objects for the specified name or an
84       empty list if the query failed or no record was found.
85
86       See "EXAMPLES" for more complete examples.
87
88   mx
89           # Use a default resolver -- can not get an error string this way.
90           use Net::DNS;
91           my @mx = mx("example.com");
92
93           # Use your own resolver object.
94           my $res = Net::DNS::Resolver->new;
95           my @mx  = mx($res, "example.com");
96
97       Returns a list of Net::DNS::RR::MX objects representing the MX records
98       for the specified name.  The list will be sorted by preference.
99       Returns an empty list if the query failed or no MX record was found.
100
101       This method does not look up A records; it only performs MX queries.
102

Dynamic DNS Update Support

104       The Net::DNS module provides auxiliary functions which support dynamic
105       DNS update requests.
106
107   yxrrset
108       Use this method to add an "RRset exists" prerequisite to a dynamic
109       update packet.  There are two forms, value-independent and value-
110       dependent:
111
112           # RRset exists (value-independent)
113           $update->push(pre => yxrrset("host.example.com A"));
114
115       Meaning:  At least one RR with the specified name and type must exist.
116
117           # RRset exists (value-dependent)
118           $update->push(pre => yxrrset("host.example.com A 10.1.2.3"));
119
120       Meaning:  At least one RR with the specified name and type must exist
121       and must have matching data.
122
123       Returns a Net::DNS::RR object or "undef" if the object could not be
124       created.
125
126   nxrrset
127       Use this method to add an "RRset does not exist" prerequisite to a
128       dynamic update packet.
129
130           $update->push(pre => nxrrset("host.example.com A"));
131
132       Meaning:  No RRs with the specified name and type can exist.
133
134       Returns a Net::DNS::RR object or "undef" if the object could not be
135       created.
136
137   yxdomain
138       Use this method to add a "name is in use" prerequisite to a dynamic
139       update packet.
140
141           $update->push(pre => yxdomain("host.example.com"));
142
143       Meaning:  At least one RR with the specified name must exist.
144
145       Returns a Net::DNS::RR object or "undef" if the object could not be
146       created.
147
148   nxdomain
149       Use this method to add a "name is not in use" prerequisite to a dynamic
150       update packet.
151
152           $update->push(pre => nxdomain("host.example.com"));
153
154       Meaning:  No RR with the specified name can exist.
155
156       Returns a Net::DNS::RR object or "undef" if the object could not be
157       created.
158
159   rr_add
160       Use this method to add RRs to a zone.
161
162           $update->push(update => rr_add("host.example.com A 10.1.2.3"));
163
164       Meaning:  Add this RR to the zone.
165
166       RR objects created by this method should be added to the "update"
167       section of a dynamic update packet.  The TTL defaults to 86400 seconds
168       (24 hours) if not specified.
169
170       Returns a Net::DNS::RR object or "undef" if the object could not be
171       created.
172
173   rr_del
174       Use this method to delete RRs from a zone.  There are three forms:
175       delete all RRsets, delete an RRset, and delete a specific RR.
176
177           # Delete all RRsets.
178           $update->push(update => rr_del("host.example.com"));
179
180       Meaning:  Delete all RRs having the specified name.
181
182           # Delete an RRset.
183           $update->push(update => rr_del("host.example.com A"));
184
185       Meaning:  Delete all RRs having the specified name and type.
186
187           # Delete a specific RR.
188           $update->push(update => rr_del("host.example.com A 10.1.2.3"));
189
190       Meaning:  Delete all RRs having the specified name, type, and data.
191
192       RR objects created by this method should be added to the "update"
193       section of a dynamic update packet.
194
195       Returns a Net::DNS::RR object or "undef" if the object could not be
196       created.
197

Zone Serial Number Management

199       The Net::DNS module provides auxiliary functions which support policy-
200       driven zone serial numbering regimes.
201
202   SEQUENTIAL
203           $successor = $soa->serial( SEQUENTIAL );
204
205       The existing serial number is incremented modulo 2**32.
206
207   UNIXTIME
208           $successor = $soa->serial( UNIXTIME );
209
210       The Unix time scale will be used as the basis for zone serial
211       numbering. The serial number will be incremented if the time elapsed
212       since the previous update is less than one second.
213
214   YYYYMMDDxx
215           $successor = $soa->serial( YYYYMMDDxx );
216
217       The 32 bit value returned by the auxiliary "YYYYMMDDxx()" function will
218       be used as the base for the date-coded zone serial number.  Serial
219       number increments must be limited to 100 per day for the date
220       information to remain useful.
221

Sorting of RR arrays

223       "rrsort()" provides functionality to help you sort RR arrays. In most
224       cases this will give you the answer that you want, but you can specify
225       your own sorting method by using the
226       "Net::DNS::RR::FOO->set_rrsort_func()" class method. See Net::DNS::RR
227       for details.
228
229   rrsort
230           use Net::DNS;
231
232           my @sorted = rrsort( $rrtype, $attribute, @rr_array );
233
234       "rrsort()" selects all RRs from the input array that are of the type
235       defined by the first argument. Those RRs are sorted based on the
236       attribute that is specified as second argument.
237
238       There are a number of RRs for which the sorting function is defined in
239       the code.
240
241       For instance:
242
243           my @prioritysorted = rrsort( "SRV", "priority", @rr_array );
244
245       returns the SRV records sorted from lowest to highest priority and for
246       equal priorities from highest to lowest weight.
247
248       If the function does not exist then a numerical sort on the attribute
249       value is performed.
250
251           my @portsorted = rrsort( "SRV", "port", @rr_array );
252
253       If the attribute is not defined then either the "default_sort()"
254       function or "canonical sorting" (as defined by DNSSEC) will be used.
255
256       "rrsort()" returns a sorted array containing only elements of the
257       specified RR type.  Any other RR types are silently discarded.
258
259       "rrsort()" returns an empty list when arguments are incorrect.
260

EXAMPLES

262       The following brief examples illustrate some of the features of
263       Net::DNS.  The documentation for individual modules and the demo
264       scripts included with the distribution provide more extensive examples.
265
266       See Net::DNS::Update for an example of performing dynamic updates.
267
268   Look up host addresses.
269           use Net::DNS;
270           my $res   = Net::DNS::Resolver->new;
271           my $reply = $res->search("www.example.com", "A");
272
273           if ($reply) {
274               foreach my $rr ($reply->answer) {
275                   print $rr->address, "\n" if $rr->can("address");
276               }
277           } else {
278               warn "query failed: ", $res->errorstring, "\n";
279           }
280
281   Find the nameservers for a domain.
282           use Net::DNS;
283           my $res   = Net::DNS::Resolver->new;
284           my $reply = $res->query("example.com", "NS");
285
286           if ($reply) {
287               foreach $rr (grep { $_->type eq "NS" } $reply->answer) {
288                   print $rr->nsdname, "\n";
289               }
290           } else {
291               warn "query failed: ", $res->errorstring, "\n";
292           }
293
294   Find the MX records for a domain.
295           use Net::DNS;
296           my $name = "example.com";
297           my $res  = Net::DNS::Resolver->new;
298           my @mx   = mx($res, $name);
299
300           if (@mx) {
301               foreach $rr (@mx) {
302                   print $rr->preference, "\t", $rr->exchange, "\n";
303               }
304           } else {
305               warn "Can not find MX records for $name: ", $res->errorstring, "\n";
306           }
307
308   Print domain SOA record in zone file format.
309           use Net::DNS;
310           my $res   = Net::DNS::Resolver->new;
311           my $reply = $res->query("example.com", "SOA");
312
313           if ($reply) {
314               foreach my $rr ($reply->answer) {
315                   $rr->print;
316               }
317           } else {
318               warn "query failed: ", $res->errorstring, "\n";
319           }
320
321   Perform a zone transfer and print all the records.
322           use Net::DNS;
323           my $res  = Net::DNS::Resolver->new;
324           $res->tcp_timeout(20);
325           $res->nameservers("ns.example.com");
326
327           my @zone = $res->axfr("example.com");
328
329           foreach $rr (@zone) {
330               $rr->print;
331           }
332
333           warn $res->errorstring if $res->errorstring;
334
335   Perform a background query and print the reply.
336           use Net::DNS;
337           my $res    = Net::DNS::Resolver->new;
338           $res->udp_timeout(10);
339           $res->tcp_timeout(20);
340           my $socket = $res->bgsend("host.example.com");
341
342           while ( $res->bgbusy($socket) ) {
343               # do some work here while waiting for the answer
344               # ...and some more here
345           }
346
347           my $packet = $res->bgread($socket);
348           if ($packet) {
349               $packet->print;
350           } else {
351               warn "query failed: ", $res->errorstring, "\n";
352           }
353

BUGS

355       Net::DNS is slow.
356
357       For other items to be fixed, or if you discover a bug in this
358       distribution please use the CPAN bug reporting system.
359

COPYRIGHT

361       Copyright (c)1997-2000 Michael Fuhr.
362
363       Portions Copyright (c)2002,2003 Chris Reinhardt.
364
365       Portions Copyright (c)2005 Olaf Kolkman (RIPE NCC)
366
367       Portions Copyright (c)2006 Olaf Kolkman (NLnet Labs)
368
369       Portions Copyright (c)2014 Dick Franks
370
371       All rights reserved.
372

LICENSE

374       Permission to use, copy, modify, and distribute this software and its
375       documentation for any purpose and without fee is hereby granted,
376       provided that the above copyright notice appear in all copies and that
377       both that copyright notice and this permission notice appear in
378       supporting documentation, and that the name of the author not be used
379       in advertising or publicity pertaining to distribution of the software
380       without specific prior written permission.
381
382       THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
383       OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
384       MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
385       IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
386       CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
387       TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
388       SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
389

AUTHOR INFORMATION

391       Net::DNS is maintained at NLnet Labs (www.nlnetlabs.nl) by Willem
392       Toorop.
393
394       Between 2005 and 2012 Net::DNS was maintained by Olaf Kolkman.
395
396       Between 2002 and 2004 Net::DNS was maintained by Chris Reinhardt.
397
398       Net::DNS was created in 1997 by Michael Fuhr.
399