Net::DNS::Resolver(3pm)

1Net::DNS::Resolver(3) User Contributed Perl DocumentationNet::DNS::Resolver(3)
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NAME

6       Net::DNS::Resolver - DNS resolver class
7

SYNOPSIS

9           use Net::DNS;
10
11           $resolver = new Net::DNS::Resolver();
12
13           # Perform a lookup, using the searchlist if appropriate.
14           $reply = $resolver->search( 'example.com' );
15
16           # Perform a lookup, without the searchlist
17           $reply = $resolver->query( 'example.com', 'MX' );
18
19           # Perform a lookup, without pre or post-processing
20           $reply = $resolver->send( 'example.com', 'MX', 'IN' );
21
22           # Send a prebuilt query packet
23           $query = new Net::DNS::Packet( ... );
24           $reply = $resolver->send( $query );
25

DESCRIPTION

27       Instances of the Net::DNS::Resolver class represent resolver objects.
28       A program can have multiple resolver objects, each maintaining its own
29       state information such as the nameservers to be queried, whether
30       recursion is desired, etc.
31

METHODS

33   new
34           # Use the default configuration
35           $resolver = new Net::DNS::Resolver();
36
37           # Use my own configuration file
38           $resolver = new Net::DNS::Resolver( config_file => '/my/dns.conf' );
39
40           # Set options in the constructor
41           $resolver = new Net::DNS::Resolver(
42               nameservers => [ '10.1.1.128', '10.1.2.128' ],
43               recurse     => 0,
44               debug       => 1
45               );
46
47       Returns a resolver object.  If no arguments are supplied, "new()"
48       returns an object having the default configuration.
49
50       On Unix and Linux systems, the default values are read from the
51       following files, in the order indicated:
52
53           /etc/resolv.conf, $HOME/.resolv.conf, ./.resolv.conf
54
55       The following keywords are recognised in resolver configuration files:
56
57           nameserver address
58
59           IP address of a name server that the resolver should query.
60
61           domain localdomain
62
63           The domain suffix to be appended to a short non-absolute name.
64
65           search domain ...
66
67           A space-separated list of domains in the desired search path.
68
69           options option:value ...
70
71           A space-separated list of key:value items.
72
73       Except for /etc/resolv.conf, files will only be read if owned by the
74       effective userid running the program.  In addition, several environment
75       variables may contain configuration information; see "ENVIRONMENT".
76
77       Note that the domain and searchlist keywords are mutually exclusive.
78       If both are present, the resulting behaviour is unspecified.  If
79       neither is present, the domain is determined from the local hostname.
80
81       On Windows systems, an attempt is made to determine the system defaults
82       using the registry.  Systems with many dynamically configured network
83       interfaces may confuse Net::DNS.
84
85           # Use my own configuration file
86           $resolver = new Net::DNS::Resolver( config_file => '/my/dns.conf' );
87
88       You can include a configuration file of your own when creating a
89       resolver object.  This is supported on both Unix and Windows.
90
91       If a custom configuration file is specified at first instantiation, all
92       other configuration files and environment variables are ignored.
93
94           # Set options in the constructor
95           $resolver = new Net::DNS::Resolver(
96               nameservers => [ '10.1.1.128', '10.1.2.128' ],
97               recurse     => 0
98               );
99
100       Explicit arguments to "new()" override the corresponding configuration
101       variables.  The argument list consists of a sequence of (name=>value)
102       pairs, each interpreted as an invocation of the corresponding method.
103
104   print
105           $resolver->print;
106
107       Prints the resolver state on the standard output.
108
109   query
110           $packet = $resolver->query( 'mailhost' );
111           $packet = $resolver->query( 'mailhost.example.com' );
112           $packet = $resolver->query( '192.0.2.1' );
113           $packet = $resolver->query( 'example.com', 'MX' );
114           $packet = $resolver->query( 'annotation.example.com', 'TXT', 'IN' );
115
116       Performs a DNS query for the given name; the search list is not
117       applied.  If "defnames" is true, and the number of dots is less than
118       "ndots", the default domain will be appended unless name is absolute.
119
120       The record type and class can be omitted; they default to A and IN.  If
121       the name looks like an IP address (IPv4 or IPv6), then a query within
122       in-addr.arpa or ip6.arpa will be performed.
123
124       Returns a Net::DNS::Packet object, or "undef" if no answers were found.
125       The reason for failure may be determined using "errorstring()".
126
127       If you need to examine the response packet, whether it contains any
128       answers or not, use the "send()" method instead.
129
130   search
131           $packet = $resolver->search( 'mailhost' );
132           $packet = $resolver->search( 'mailhost.example.com' );
133           $packet = $resolver->search( '192.0.2.1' );
134           $packet = $resolver->search( 'example.com', 'MX' );
135           $packet = $resolver->search( 'annotation.example.com', 'TXT', 'IN' );
136
137       Performs a DNS query for the given name, applying the searchlist if
138       appropriate.  The search algorithm is as follows:
139
140       Unless the number of dots is less than "ndots", perform an initial
141       query using the unmodified name.
142
143       If "dnsrch" is true and the name has no terminal dot, try appending
144       each suffix in the search list.
145
146       The record type and class can be omitted; they default to A and IN.  If
147       the name looks like an IP address (IPv4 or IPv6), then a query within
148       in-addr.arpa or ip6.arpa will be performed.
149
150       Returns a Net::DNS::Packet object, or "undef" if no answers were found.
151       The reason for failure may be determined using "errorstring()".
152
153       If you need to examine the response packet, whether it contains any
154       answers or not, use the "send()" method instead.
155
156   send
157           $packet = $resolver->send( $query );
158
159           $packet = $resolver->send( 'mailhost.example.com' );
160           $packet = $resolver->query( '192.0.2.1' );
161           $packet = $resolver->send( 'example.com', 'MX' );
162           $packet = $resolver->send( 'annotation.example.com', 'TXT', 'IN' );
163
164       Performs a DNS query for the given name.  Neither the searchlist nor
165       the default domain will be appended.
166
167       The argument list can be either a pre-built query Net::DNS::Packet or a
168       list of strings.  The record type and class can be omitted; they
169       default to A and IN.  If the name looks like an IP address (IPv4 or
170       IPv6), then a query within in-addr.arpa or ip6.arpa will be performed.
171
172       Returns a Net::DNS::Packet object whether there were any answers or
173       not.  Use "$packet->header->ancount" or "$packet->answer" to find out
174       if there were any records in the answer section.  Returns "undef" if no
175       response was received.
176
177   axfr
178           @zone = $resolver->axfr();
179           @zone = $resolver->axfr( 'example.com' );
180           @zone = $resolver->axfr( 'example.com', 'IN' );
181
182           $iterator = $resolver->axfr();
183           $iterator = $resolver->axfr( 'example.com' );
184           $iterator = $resolver->axfr( 'example.com', 'IN' );
185
186           $rr = $iterator->();
187
188       Performs a zone transfer using the resolver nameservers list, attempted
189       in the order listed.
190
191       If the zone is omitted, it defaults to the first zone listed in the
192       resolver search list.
193
194       If the class is omitted, it defaults to IN.
195
196       When called in list context, "axfr()" returns a list of Net::DNS::RR
197       objects.  The redundant SOA record that terminates the zone transfer is
198       not returned to the caller.
199
200       In deferrence to RFC1035(6.3), a complete zone transfer is expected to
201       return all records in the zone or nothing at all.  When no resource
202       records are returned by "axfr()", the reason for failure may be
203       determined using "errorstring()".
204
205       Here is an example that uses a timeout and TSIG verification:
206
207           $resolver->tcp_timeout( 10 );
208           $resolver->tsig( 'Khmac-sha1.example.+161+24053.private' );
209           @zone = $resolver->axfr( 'example.com' );
210
211           foreach $rr (@zone) {
212               $rr->print;
213           }
214
215       When called in scalar context, "axfr()" returns an iterator object.
216       Each invocation of the iterator returns a single Net::DNS::RR or
217       "undef" when the zone is exhausted.
218
219       An exception is raised if the zone transfer can not be completed.
220
221       The redundant SOA record that terminates the zone transfer is not
222       returned to the caller.
223
224       Here is the example above, implemented using an iterator:
225
226           $resolver->tcp_timeout( 10 );
227           $resolver->tsig( 'Khmac-sha1.example.+161+24053.private' );
228           $iterator = $resolver->axfr( 'example.com' );
229
230           while ( $rr = $iterator->() ) {
231               $rr->print;
232           }
233
234   bgsend
235           $handle = $resolver->bgsend( $packet ) || die $resolver->errorstring;
236
237           $handle = $resolver->bgsend( 'mailhost.example.com' );
238           $handle = $resolver->bgsend( '192.0.2.1' );
239           $handle = $resolver->bgsend( 'example.com', 'MX' );
240           $handle = $resolver->bgsend( 'annotation.example.com', 'TXT', 'IN' );
241
242       Performs a background DNS query for the given name and returns
243       immediately without waiting for the response. The program can then
244       perform other tasks while awaiting the response from the nameserver.
245
246       The argument list can be either a Net::DNS::Packet object or a list of
247       strings.  The record type and class can be omitted; they default to A
248       and IN.  If the name looks like an IP address (IPv4 or IPv6), then a
249       query within in-addr.arpa or ip6.arpa will be performed.
250
251       Returns an opaque handle which is passed to subsequent invocations of
252       the "bgbusy()" and "bgread()" methods.  Errors are indicated by
253       returning "undef" in which case the reason for failure may be
254       determined using "errorstring()".
255
256       The response Net::DNS::Packet object is obtained by calling "bgread()".
257
258       BEWARE: Programs should make no assumptions about the nature of the
259       handles returned by "bgsend()" which should be used strictly as
260       described here.
261
262   bgread
263           $handle = $resolver->bgsend( 'www.example.com' );
264           $packet = $resolver->bgread($handle);
265
266       Reads the answer from a background query.  The argument is the handle
267       returned by "bgsend()".
268
269       Returns a Net::DNS::Packet object or "undef" if no response was
270       received before the timeout interval expired.
271
272   bgbusy
273           $handle = $resolver->bgsend( 'foo.example.com' );
274
275           while ($resolver->bgbusy($handle)) {
276               ...
277           }
278
279           $packet = $resolver->bgread($handle);
280
281       Returns true while awaiting the response or for the transaction to time
282       out.  The argument is the handle returned by "bgsend()".
283
284       Truncated UDP packets will be retried transparently using TCP while
285       continuing to assert busy to the caller.
286
287   bgisready
288           until ($resolver->bgisready($handle)) {
289               ...
290           }
291
292       "bgisready()" is the logical complement of "bgbusy()" which is retained
293       for backward compatibility.
294
295   debug
296           print 'debug flag: ', $resolver->debug, "\n";
297           $resolver->debug(1);
298
299       Get or set the debug flag.  If set, calls to "search()", "query()", and
300       "send()" will print debugging information on the standard output.  The
301       default is false.
302
303   defnames
304           print 'defnames flag: ', $resolver->defnames, "\n";
305           $resolver->defnames(0);
306
307       Get or set the defnames flag.  If true, calls to "query()" will append
308       the default domain to resolve names that are not fully qualified.  The
309       default is true.
310
311   dnsrch
312           print 'dnsrch flag: ', $resolver->dnsrch, "\n";
313           $resolver->dnsrch(0);
314
315       Get or set the dnsrch flag.  If true, calls to "search()" will apply
316       the search list to resolve names that are not fully qualified.  The
317       default is true.
318
319   domain
320           $domain = $resolver->domain;
321           $resolver->domain( 'domain.example' );
322
323       Gets or sets the resolver default domain.
324
325   igntc
326           print 'igntc flag: ', $resolver->igntc, "\n";
327           $resolver->igntc(1);
328
329       Get or set the igntc flag.  If true, truncated packets will be ignored.
330       If false, the query will be retried using TCP.  The default is false.
331
332   nameserver, nameservers
333           @nameservers = $resolver->nameservers();
334           $resolver->nameservers( '192.0.2.1', '192.0.2.2', '2001:DB8::3' );
335
336       Gets or sets the nameservers to be queried.
337
338       Also see the IPv6 transport notes below
339
340   persistent_tcp
341           print 'Persistent TCP flag: ', $resolver->persistent_tcp, "\n";
342           $resolver->persistent_tcp(1);
343
344       Get or set the persistent TCP setting.  If true, Net::DNS will keep a
345       TCP socket open for each host:port to which it connects.  This is
346       useful if you are using TCP and need to make a lot of queries or
347       updates to the same nameserver.
348
349       The default is false unless you are running a SOCKSified Perl, in which
350       case the default is true.
351
352   persistent_udp
353           print 'Persistent UDP flag: ', $resolver->persistent_udp, "\n";
354           $resolver->persistent_udp(1);
355
356       Get or set the persistent UDP setting.  If true, a Net::DNS resolver
357       will use the same UDP socket for all queries within each address
358       family.
359
360       This avoids the cost of creating and tearing down UDP sockets, but also
361       defeats source port randomisation.
362
363   port
364           print 'sending queries to port ', $resolver->port, "\n";
365           $resolver->port(9732);
366
367       Gets or sets the port to which queries are sent.  Convenient for
368       nameserver testing using a non-standard port.  The default is port 53.
369
370   recurse
371           print 'recursion flag: ', $resolver->recurse, "\n";
372           $resolver->recurse(0);
373
374       Get or set the recursion flag.  If true, this will direct nameservers
375       to perform a recursive query.  The default is true.
376
377   retrans
378           print 'retrans interval: ', $resolver->retrans, "\n";
379           $resolver->retrans(3);
380
381       Get or set the retransmission interval The default is 5 seconds.
382
383   retry
384           print 'number of tries: ', $resolver->retry, "\n";
385           $resolver->retry(2);
386
387       Get or set the number of times to try the query.  The default is 4.
388
389   searchlist
390           @searchlist = $resolver->searchlist;
391           $resolver->searchlist( 'a.example', 'b.example', 'c.example' );
392
393       Gets or sets the resolver search list.
394
395   srcaddr
396           $resolver->srcaddr('192.0.2.1');
397
398       Sets the source address from which queries are sent.  Convenient for
399       forcing queries from a specific interface on a multi-homed host.  The
400       default is to use any local address.
401
402   srcport
403           $resolver->srcport(5353);
404
405       Sets the port from which queries are sent.  The default is 0, meaning
406       any port.
407
408   tcp_timeout
409           print 'TCP timeout: ', $resolver->tcp_timeout, "\n";
410           $resolver->tcp_timeout(10);
411
412       Get or set the TCP timeout in seconds.  The default is 120 seconds (2
413       minutes).
414
415   udp_timeout
416           print 'UDP timeout: ', $resolver->udp_timeout, "\n";
417           $resolver->udp_timeout(10);
418
419       Get or set the bgsend() UDP timeout in seconds.  The default is 30
420       seconds.
421
422   udppacketsize
423           print "udppacketsize: ", $resolver->udppacketsize, "\n";
424           $resolver->udppacketsize(2048);
425
426       Get or set the UDP packet size.  If set to a value not less than the
427       default DNS packet size, an EDNS extension will be added indicating
428       support for large UDP datagrams.
429
430   usevc
431           print 'usevc flag: ', $resolver->usevc, "\n";
432           $resolver->usevc(1);
433
434       Get or set the usevc flag.  If true, queries will be performed using
435       virtual circuits (TCP) instead of datagrams (UDP).  The default is
436       false.
437
438   answerfrom
439           print 'last answer was from: ', $resolver->answerfrom, "\n";
440
441       Returns the IP address from which the most recent packet was received
442       in response to a query.
443
444   errorstring
445           print 'query status: ', $resolver->errorstring, "\n";
446
447       Returns a string containing error information from the most recent DNS
448       protocol interaction.  "errorstring()" is meaningful only when
449       interrogated immediately after the corresponding method call.
450
451   dnssec
452           print "dnssec flag: ", $resolver->dnssec, "\n";
453           $resolver->dnssec(0);
454
455       The dnssec flag causes the resolver to transmit DNSSEC queries and to
456       add a EDNS0 record as required by RFC2671 and RFC3225.  The actions of,
457       and response from, the remote nameserver is determined by the settings
458       of the AD and CD flags.
459
460       Calling the "dnssec()" method with a non-zero value will also set the
461       UDP packet size to the default value of 2048. If that is too small or
462       too big for your environment, you should call the "udppacketsize()"
463       method immediately after.
464
465          $resolver->dnssec(1);                # DNSSEC using default packetsize
466          $resolver->udppacketsize(1250);      # lower the UDP packet size
467
468       A fatal exception will be raised if the "dnssec()" method is called but
469       the Net::DNS::SEC library has not been installed.
470
471   adflag
472           $resolver->dnssec(1);
473           $resolver->adflag(1);
474           print "authentication desired flag: ", $resolver->adflag, "\n";
475
476       Gets or sets the AD bit for dnssec queries.  This bit indicates that
477       the caller is interested in the returned AD (authentic data) bit but
478       does not require any dnssec RRs to be included in the response.  The
479       default value is false.
480
481   cdflag
482           $resolver->dnssec(1);
483           $resolver->cdflag(1);
484           print "checking disabled flag: ", $resolver->cdflag, "\n";
485
486       Gets or sets the CD bit for dnssec queries.  This bit indicates that
487       authentication by upstream nameservers should be suppressed.  Any
488       dnssec RRs required to execute the authentication procedure should be
489       included in the response.  The default value is false.
490
491   tsig
492           $resolver->tsig( $tsig );
493
494           $resolver->tsig( 'Khmac-sha1.example.+161+24053.private' );
495
496           $resolver->tsig( 'Khmac-sha1.example.+161+24053.key' );
497
498           $resolver->tsig( 'Khmac-sha1.example.+161+24053.key',
499                       fudge => 60
500                       );
501
502           $resolver->tsig( $key_name, $key );
503
504           $resolver->tsig( undef );
505
506       Set the TSIG record used to automatically sign outgoing queries, zone
507       transfers and updates. Automatic signing is disabled if called with
508       undefined arguments.
509
510       The default resolver behaviour is not to sign any packets.  You must
511       call this method to set the key if you would like the resolver to sign
512       and verify packets automatically.
513
514       Packets can also be signed manually; see the Net::DNS::Packet and
515       Net::DNS::Update manual pages for examples.  TSIG records in manually-
516       signed packets take precedence over those that the resolver would add
517       automatically.
518

ENVIRONMENT

520       The following environment variables can also be used to configure the
521       resolver:
522
523   RES_NAMESERVERS
524           # Bourne Shell
525           RES_NAMESERVERS="192.0.2.1 192.0.2.2 2001:DB8::3"
526           export RES_NAMESERVERS
527
528           # C Shell
529           setenv RES_NAMESERVERS "192.0.2.1 192.0.2.2 2001:DB8::3"
530
531       A space-separated list of nameservers to query.
532
533   RES_SEARCHLIST
534           # Bourne Shell
535           RES_SEARCHLIST="a.example.com b.example.com c.example.com"
536           export RES_SEARCHLIST
537
538           # C Shell
539           setenv RES_SEARCHLIST "a.example.com b.example.com c.example.com"
540
541       A space-separated list of domains to put in the search list.
542
543   LOCALDOMAIN
544           # Bourne Shell
545           LOCALDOMAIN=example.com
546           export LOCALDOMAIN
547
548           # C Shell
549           setenv LOCALDOMAIN example.com
550
551       The default domain.
552
553   RES_OPTIONS
554           # Bourne Shell
555           RES_OPTIONS="retrans:3 retry:2 inet6"
556           export RES_OPTIONS
557
558           # C Shell
559           setenv RES_OPTIONS "retrans:3 retry:2 inet6"
560
561       A space-separated list of resolver options to set.  Options that take
562       values are specified as "option:value".
563

IPv6 TRANSPORT

565       The Net::DNS::Resolver library will enable IPv6 transport if the
566       IO::Socket::IP library package is available.
567
568       The "force_v4()", "force_v6()", "prefer_v4()", and "prefer_v6()"
569       methods with non-zero argument may be used to configure transport
570       selection.
571
572       The behaviour of the "nameserver()" method illustrates the transport
573       selection mechanism.  If, for example, IPv6 is not available or IPv4
574       transport has been forced, the "nameserver()" method will only return
575       IPv4 addresses:
576
577           $resolver->nameservers( '192.0.2.1', '192.0.2.2', '2001:DB8::3' );
578           $resolver->force_v4(1);
579           print join ' ', $resolver->nameservers();
580
581       will print
582
583           192.0.2.1 192.0.2.2
584

CUSTOMISED RESOLVERS

586       Net::DNS::Resolver is actually an empty subclass.  At compile time a
587       super class is chosen based on the current platform.  A side benefit of
588       this allows for easy modification of the methods in Net::DNS::Resolver.
589       You can simply add a method to the namespace!
590
591       For example, if we wanted to cache lookups:
592
593           package Net::DNS::Resolver;
594
595           my %cache;
596
597           sub search {
598               $self = shift;
599
600               $cache{"@_"} ||= $self->SUPER::search(@_);
601           }
602

COPYRIGHT

604       Copyright (c)1997-2000 Michael Fuhr.
605
606       Portions Copyright (c)2002-2004 Chris Reinhardt.
607
608       Portions Copyright (c)2005 Olaf M. Kolkman, NLnet Labs.
609
610       Portions Copyright (c)2014,2015 Dick Franks.
611
612       All rights reserved.
613

LICENSE

615       Permission to use, copy, modify, and distribute this software and its
616       documentation for any purpose and without fee is hereby granted,
617       provided that the above copyright notice appear in all copies and that
618       both that copyright notice and this permission notice appear in
619       supporting documentation, and that the name of the author not be used
620       in advertising or publicity pertaining to distribution of the software
621       without specific prior written permission.
622
623       THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
624       OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
625       MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
626       IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
627       CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
628       TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
629       SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
630