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, Net::DNS, Net::DNS::Resolver, Net::DNS::Packet, Net::DNS::Update, Net::DNS::Header, Net::DNS::Question, Net::DNS::RR, RFC 1035