NAME

Net::DNS::Nameserver - DNS server class

SYNOPSIS

    use Net::DNS::Nameserver;

    my $nameserver = Net::DNS::Nameserver->new(
	LocalAddr	=> ['::1', '127.0.0.1'],
	LocalPort	=> 15353,
	ZoneFile	=> 'filename'
	);

    my $nameserver = Net::DNS::Nameserver->new(
	LocalAddr	=> '10.1.2.3',
	LocalPort	=> 15353,
	ReplyHandler	=> \&reply_handler
    );

    $nameserver->start_server($timeout);
    $nameserver->stop_server;

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 /EXAMPLES below for further details.

METHODS

new

    $nameserver = Net::DNS::Nameserver->new(
	LocalAddr	=> ['::1', '127.0.0.1'],
	LocalPort	=> 15353,
	ZoneFile	=> "filename"
	);

    $nameserver = Net::DNS::Nameserver->new(
	LocalAddr	=> '10.1.2.3',
	LocalPort	=> 15353,
	ReplyHandler	=> \&reply_handler,
	Verbose		=> 1,
	Truncate	=> 0
    );

Instantiates a Net::DNS::Nameserver object. An exception is raised 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
    ZoneFile		Name of file containing RRs
			accessed using the internal
			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)

The LocalAddr attribute may alternatively be specified as an array of IP addresses to listen to.

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 the optionmask: {$optioncode => $value, $optionname => $value}

See RFC1035 and IANA DNS parameters file for more information:

The nameserver will listen for both UDP and TCP connections. On linux and other Unix-like systems, unprivileged users are denied access to ports below 1024.

UDP reply truncation functionality was introduced in Net::DNS 0.66. 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=>0 and truncate the reply packet in the code of the ReplyHandler.

start_server

    $ns->start_server(  );

Starts a server process for each of the specified UDP and TCP sockets which continuously responds to user connections.

The timeout parameter specifies the time the server is to remain active. If called with no parameter a default timeout of 10 minutes is applied.

stop_server

    $ns->stop_server();

Terminates all server processes in an orderly fashion.

EXAMPLES

Example 1: Test script with embedded nameserver

The following example is a self-contained test script which queries DNS zonefile data served by an embedded Net::DNS::Nameserver instance.

    use strict;
    use warnings;
    use Test::More;

    plan skip_all => 'Net::DNS::Nameserver not available'
		unless eval { require Net::DNS::Nameserver }
		and Net::DNS::Nameserver->can('start_server');
    plan tests => 2;

    my $resolver = Net::DNS::Resolver->new(
	nameserver => ['::1', '127.0.0.1'],
	port	   => 15353
	);
 

    my $ns = Net::DNS::Nameserver->new(
	LocalAddr => [$resolver->nameserver],
	LocalPort => $resolver->port,
	Verbose	  => 0,
	ZoneFile  => \*DATA
	)
		|| die "couldn't create nameserver object";

    $ns->start_server(10);

    my $reply = $resolver->send(qw(example.com SOA));
    is( ref($reply), 'Net::DNS::Packet', 'received reply packet' );
    my ($rr) = $reply->answer;
    is( $rr->type, 'SOA', 'answer contains SOA record' );

    $ns->stop_server();

    exit;

    __DATA__
    $ORIGIN example.com.
    @	IN SOA	mname rname 2023 2h 1h 2w 1h
    www	IN A	93.184.216.34

Example 2: Free-standing customised DNS nameserver

The following example will listen on port 15353 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 a per-host basis may be applied.

    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    => 15353,
	ReplyHandler => \&reply_handler,
	Verbose	     => 1
	) or die "couldn't create nameserver object";

    $ns->start_server(60);

    exit;	# leaving nameserver processes running

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, the source address being chosen by the operating system based upon its notion of "closest address". This limitation is mitigated by creating a separate set of sockets and server subprocesses bound to 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)2017-2024 R.W.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 Net::DNS Net::DNS::Resolver Net::DNS::Packet Net::DNS::Update Net::DNS::Header Net::DNS::Question Net::DNS::RR