Ubuntu Manpage: Net::DNS::Nameserver

Provided by: libnet-dns-perl_0.68-1.2build1_amd64

NAME

       Net::DNS::Nameserver - DNS server class

SYNOPSIS

           use Net::DNS::Nameserver;

           $nameserver = new Net::DNS::Nameserver(
               LocalAddr        => ['::1' , '127.0.0.1' ],
               LocalPort        => "5353",
               ReplyHandler => \&reply_handler,
               Verbose          => 1,
               Truncate         => 0
           );

DESCRIPTION

       Instances of the "Net::DNS::Nameserver" class represent DNS server objects.  See "EXAMPLE"
       for an example.

METHODS

new
my $ns = new Net::DNS::Nameserver(
LocalAddr => "10.1.2.3",
LocalPort => "5353",
ReplyHandler => \&reply_handler,
Verbose => 1
);

my $ns = new Net::DNS::Nameserver(
LocalAddr => ['::1' , '127.0.0.1' ],
LocalPort => "5353",
ReplyHandler => \&reply_handler,
Verbose => 1,
Truncate => 0
);

Creates a nameserver object. Attributes are:

LocalAddr IP address on which to listen. Defaults to INADDR_ANY.
LocalPort Port on which to listen. Defaults to 53.
ReplyHandler Reference to reply-handling
subroutine Required.
NotifyHandler Reference to reply-handling
subroutine for queries with
opcode NS_NOTIFY (RFC1996)
Verbose Print info about received
queries. Defaults to 0 (off).
Truncate Truncates UDP packets that
are to 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 IO::Socket::INET6 and Socket6 are available on the system you can also list IPv6
addresses and the default is '0' (listen on all interfaces on IPv6 and IPv4);

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 }".

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.

Packet Truncation is new functionality for $Net::DNS::Nameserver::VERSION>830 and uses the
Net::DNS::Packet::truncate method with a size determinde by the advertised EDNS0 size in
the query, or 512 if EDNS0 is not advertised in the query. Only UDP replies are truncated.
If you want to do packet runcation yourself you should set Truncate to 0 and use the
truncate method on the reply packet in the code you use for the ReplyHandler.

Returns a Net::DNS::Nameserver object, or undef if the object couldn't be created.

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). If called with a number, that
number specifies how many seconds (even fractional) to maximum wait before returning. If
called with 0 it will return immediately unless there's something to do.

Handling a request and replying obviously depends on the speed of ReplyHandler. Assuming
ReplyHandler is super fast, loop_once should spend just a fraction of a second, if called
with a timeout value of 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 keep
running through a loop (while servicing new requests) until the reply has been sent.

In case loop_once accepted a TCP connection it will immediatly 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 authoritive (by setting the 'aa' flag
               return ($rcode, \@ans, \@auth, \@add, { aa => 1 });
           }

           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 choses. 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)1997-2002 Michael Fuhr.

       Portions Copyright (c)2002-2004 Chris Reinhardt.

       Portions Copyright (c)2005-2009 O.M, Kolkman, RIPE NCC.

       Portions Copyright (c)2005 Robert Martin-Legene.

       All rights reserved.

       This program is free software; you may redistribute it and/or modify it under the same
       terms as Perl itself.