Net::DNS::Nameserver(3)
NAME
Net::DNS::Nameserver - DNS server class
SYNOPSIS
use Net::DNS::Nameserver;
my $nameserver = Net::DNS::Nameserver->new(
LocalAddr => ['::1' , '127.0.0.1'],
ZoneFile => "filename"
);
my $nameserver = Net::DNS::Nameserver->new(
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 = Net::DNS::Nameserver->new(
LocalAddr => ['::1' , '127.0.0.1'],
ZoneFile => "filename"
);
$nameserver = Net::DNS::Nameserver->new(
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 5353
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, peerhost, query record, and connection descriptor. 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, unprivileged users are denied access to ports below 1024.
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 $rr = Net::DNS::RR->new("$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 = Net::DNS::Nameserver->new(
LocalPort => 5353,
ReplyHandler => \&reply_handler,
Verbose => 1
) || die "couldn't create nameserver object\n";
$ns->main_loop;
BUGS
Limitations in perl make it impossible to guarantee that replies to UDP
queries from Net::DNS::Nameserver are sent from the IP-address to which
the query was directed. 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 original copyright notices appear in all copies and
that both 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(1), Net::DNS(3), Net::DNS::Resolver(3), Net::DNS::Packet(3),
Net::DNS::Update(3), Net::DNS::Header(3), Net::DNS::Question(3),
Net::DNS::RR(3), RFC 1035
perl v5.30.3 2021-12-16 Net::DNS::Nameserver(3)
net-dns 1.330.0 - Generated Fri Dec 24 08:18:13 CST 2021