| Net::DNS - Perl Interface to the Domain Name System |
Net::DNS - Perl Interface to the Domain Name System
use Net::DNS;
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.
A resolver object is an instance of the the Net::DNS::Resolver manpage 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.
the Net::DNS::Resolver manpage queries return the Net::DNS::Packet manpage objects. Packet objects have five sections:
the Net::DNS::Update manpage is a subclass of the Net::DNS::Packet manpage used to create dynamic update requests.
the Net::DNS::Header manpage objects represent the header section of a DNS packet.
the Net::DNS::Question manpage objects represent the content of the question section of a DNS packet.
the Net::DNS::RR manpage 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.
See the manual pages listed above for other class-specific methods.
print Net::DNS->version, "\n";
Returns the version of Net::DNS.
# 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.
use Net::DNS;
my $res = Net::DNS::Resolver->new;
my @mx = mx($res, "example.com");
Returns a list of the Net::DNS::RR::MX manpage 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 A records; it only performs MX queries.
See EXAMPLES for a more complete example.
The Net::DNS module provides auxiliary functions which support dynamic DNS update requests.
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 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 the Net::DNS::RR manpage object or undef if the object could not
be created.
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 the Net::DNS::RR manpage object or undef if the object could not
be created.
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 the Net::DNS::RR manpage object or undef if the object could not
be created.
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 the Net::DNS::RR manpage object or undef if the object could not
be created.
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 the Net::DNS::RR manpage object or undef if the object could not
be created.
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 the Net::DNS::RR manpage object or undef if the object could not
be created.
The Net::DNS module provides auxiliary functions which support policy-driven zone serial numbering regimes.
$successor = $soa->serial( SEQUENTIAL );
The existing serial number is incremented modulo 2**32.
$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.
$successor = $soa->serial( YYYYMMDDxx );
The 32 bit value returned by the auxiliary 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.
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 the Net::DNS::RR::FOO->set_rrsort_func()
class method. See Net::DNS::RR for details.
rrsort()
use Net::DNS qw(rrsort);
@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. The function can be overidden using the set_rrsort_func() method.
For instance:
@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.
@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 or undef.
rrsort() returns undef when arguments are incorrect.
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.
use Net::DNS;
my $res = Net::DNS::Resolver->new;
my $reply = $res->search("host.example.com");
if ($reply) {
foreach my $rr ($reply->answer) {
next unless $rr->type eq "A";
print $rr->address, "\n";
}
} else {
warn "query failed: ", $res->errorstring, "\n";
}
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";
}
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 not find MX records for $name: ", $res->errorstring, "\n";
}
use Net::DNS;
my $res = Net::DNS::Resolver->new;
my $reply = $res->query("example.com", "SOA");
if ($reply) {
($reply->answer)[0]->print;
} else {
print "query failed: ", $res->errorstring, "\n";
}
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;
}
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;
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 {
warn "timed out after $timeout seconds\n";
}
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 (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.
Permission to use, copy, modify, and distribute this software and its documentation for any purpose and without fee is hereby granted, provided that the above copyright notice appear in all copies and that both that 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.
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.
the perl manpage, the Net::DNS::Resolver manpage, the Net::DNS::Question manpage, the Net::DNS::RR manpage, the Net::DNS::Packet manpage, the Net::DNS::Update manpage, RFC1035, http://www.net-dns.org/, DNS and BIND by Paul Albitz & Cricket Liu
| Net::DNS - Perl Interface to the Domain Name System |