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
    );

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         Defaults to 5353
    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)
    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 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 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] );

Initialises the specified UDP and TCP sockets and starts the server which will respond to a single connection on each socket.

The timeout parameter specifies the maximum time to wait for a request. If called without parameters a default timeout of 10 minutes is applied. If called with a zero parameter, the timeout function is disabled.

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 a per-host basis may be applied.

    #!/usr/bin/perl -T

    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;

    exit;

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)2017,2023 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

RFC1035 <https://tools.ietf.org/html/rfc1035>

IANA DNS parameters <http://www.iana.org/assignments/dns-parameters>