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Net::DNS::Nameserver(3pm) User Contributed Perl Documentation Net::DNS::Nameserver(3pm)
NAME
Net::DNS::Nameserver - DNS server class
SYNOPSIS
use Net::DNS::Nameserver;
my $nameserver = new Net::DNS::Nameserver(
LocalAddr => ['::1' , '127.0.0.1'],
ZoneFile => "filename"
);
my $nameserver = new Net::DNS::Nameserver(
LocalAddr => '10.1.2.3',
LocalPort => 5353,
ReplyHandler => \&reply_handler
);
DESCRIPTION
Net::DNS::Nameserver offers a simple mechanism for instantiation of customised DNS server
objects intended to provide test responses to queries emanating from a client resolver.
It is not, nor will it ever be, a general-purpose DNS nameserver implementation.
See "EXAMPLE" for an example.
METHODS
new
$nameserver = new Net::DNS::Nameserver(
LocalAddr => ['::1' , '127.0.0.1'],
ZoneFile => "filename"
);
$nameserver = new Net::DNS::Nameserver(
LocalAddr => '10.1.2.3',
LocalPort => 5353,
ReplyHandler => \&reply_handler,
Verbose => 1,
Truncate => 0
);
Returns a Net::DNS::Nameserver object, or undef if the object could not be created.
Each instance is configured using the following optional arguments:
LocalAddr IP address on which to listen Defaults to loopback address
LocalPort Port on which to listen Defaults to 53
ZoneFile Name of file containing RRs
accessed using the default
reply-handling subroutine
ReplyHandler Reference to customised
reply-handling subroutine
NotifyHandler Reference to reply-handling
subroutine for queries with
opcode NOTIFY (RFC1996)
UpdateHandler Reference to reply-handling
subroutine for queries with
opcode UPDATE (RFC2136)
Verbose Report internal activity Defaults to 0 (off)
Truncate Truncates UDP packets that
are too big for the reply Defaults to 1 (on)
IdleTimeout TCP clients are disconnected
if they are idle longer than
this duration Defaults to 120 (secs)
The LocalAddr attribute may alternatively be specified as a list of IP addresses to listen
to. If the IO::Socket::IP library package is available on the system this may also
include IPv6 addresses.
The ReplyHandler subroutine is passed the query name, query class, query type and
optionally an argument containing the peerhost, the incoming query, and the name of the
incoming socket (sockethost). It must either return the response code and references to
the answer, authority, and additional sections of the response, or undef to leave the
query unanswered. Common response codes are:
NOERROR No error
FORMERR Format error
SERVFAIL Server failure
NXDOMAIN Non-existent domain (name doesn't exist)
NOTIMP Not implemented
REFUSED Query refused
For advanced usage it may also contain a headermask containing an hashref with the
settings for the "aa", "ra", and "ad" header bits. The argument is of the form "{ ad => 1,
aa => 0, ra => 1 }".
EDNS options may be specified in a similar manner using optionmask "{ $optioncode =>
$value, $optionname => $value }".
See RFC 1035 and the IANA dns-parameters file for more information:
ftp://ftp.rfc-editor.org/in-notes/rfc1035.txt
http://www.isi.edu/in-notes/iana/assignments/dns-parameters
The nameserver will listen for both UDP and TCP connections. On Unix-like systems, the
program will probably have to run as root to listen on the default port, 53. A non-
privileged user should be able to listen on ports 1024 and higher.
UDP reply truncation functionality was introduced in VERSION 830. The size limit is
determined by the EDNS0 size advertised in the query, otherwise 512 is used. If you want
to do packet truncation yourself you should set "Truncate" to 0 and truncate the reply
packet in the code of the ReplyHandler.
See "EXAMPLE" for an example.
main_loop
$ns->main_loop;
Start accepting queries. Calling main_loop never returns.
loop_once
$ns->loop_once( [TIMEOUT_IN_SECONDS] );
Start accepting queries, but returns. If called without a parameter, the call will not
return until a request has been received (and replied to). Otherwise, the parameter
specifies the maximum time to wait for a request. A zero timeout forces an immediate
return if there is nothing to do.
Handling a request and replying obviously depends on the speed of ReplyHandler. Assuming a
fast ReplyHandler, loop_once should spend just a fraction of a second, if called with a
timeout value of 0.0 seconds. One exception is when an AXFR has requested a huge amount of
data that the OS is not ready to receive in full. In that case, it will remain in a loop
(while servicing new requests) until the reply has been sent.
In case loop_once accepted a TCP connection it will immediately check if there is data to
be read from the socket. If not it will return and you will have to call loop_once() again
to check if there is any data waiting on the socket to be processed. In most cases you
will have to count on calling "loop_once" twice.
A code fragment like:
$ns->loop_once(10);
while( $ns->get_open_tcp() ){
$ns->loop_once(0);
}
Would wait for 10 seconds for the initial connection and would then process all TCP
sockets until none is left.
get_open_tcp
In scalar context returns the number of TCP connections for which state is maintained. In
array context it returns IO::Socket objects, these could be useful for troubleshooting but
be careful using them.
EXAMPLE
The following example will listen on port 5353 and respond to all queries for A records
with the IP address 10.1.2.3. All other queries will be answered with NXDOMAIN.
Authority and additional sections are left empty. The $peerhost variable catches the IP
address of the peer host, so that additional filtering on its basis may be applied.
#!/usr/bin/perl
use strict;
use warnings;
use Net::DNS::Nameserver;
sub reply_handler {
my ( $qname, $qclass, $qtype, $peerhost, $query, $conn ) = @_;
my ( $rcode, @ans, @auth, @add );
print "Received query from $peerhost to " . $conn->{sockhost} . "\n";
$query->print;
if ( $qtype eq "A" && $qname eq "foo.example.com" ) {
my ( $ttl, $rdata ) = ( 3600, "10.1.2.3" );
my $rr = new Net::DNS::RR("$qname $ttl $qclass $qtype $rdata");
push @ans, $rr;
$rcode = "NOERROR";
} elsif ( $qname eq "foo.example.com" ) {
$rcode = "NOERROR";
} else {
$rcode = "NXDOMAIN";
}
# mark the answer as authoritative (by setting the 'aa' flag)
my $headermask = {aa => 1};
# specify EDNS options { option => value }
my $optionmask = {};
return ( $rcode, \@ans, \@auth, \@add, $headermask, $optionmask );
}
my $ns = new Net::DNS::Nameserver(
LocalPort => 5353,
ReplyHandler => \&reply_handler,
Verbose => 1
) || die "couldn't create nameserver object\n";
$ns->main_loop;
BUGS
Limitations in perl 5.8.6 makes it impossible to guarantee that replies to UDP queries
from Net::DNS::Nameserver are sent from the IP-address they were received on. This is a
problem for machines with multiple IP-addresses and causes violation of RFC2181 section 4.
Thus a UDP socket created listening to INADDR_ANY (all available IP-addresses) will reply
not necessarily with the source address being the one to which the request was sent, but
rather with the address that the operating system chooses. This is also often called "the
closest address". This should really only be a problem on a server which has more than one
IP-address (besides localhost - any experience with IPv6 complications here, would be
nice). If this is a problem for you, a work-around would be to not listen to INADDR_ANY
but to specify each address that you want this module to listen on. A separate set of
sockets will then be created for each IP-address.
COPYRIGHT
Copyright (c)2000 Michael Fuhr.
Portions Copyright (c)2002-2004 Chris Reinhardt.
Portions Copyright (c)2005 Robert Martin-Legene.
Portions Copyright (c)2005-2009 O.M, Kolkman, RIPE NCC.
Portions Copyright (c)2017 Dick Franks.
All rights reserved.
LICENSE
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.
SEE ALSO
perl, Net::DNS, Net::DNS::Resolver, Net::DNS::Packet, Net::DNS::Update, Net::DNS::Header,
Net::DNS::Question, Net::DNS::RR, RFC 1035
perl v5.30.0 2020-02-22 Net::DNS::Nameserver(3pm)
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On Apache
Under GNU General Public License
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