Net::DNS::Nameserver(3User Contributed Perl DocumentatiNet::DNS::Nameserver(3)NAMENet::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 NOTIFY (RFC1996)
Verbose Print info about received
queries. 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 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
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)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.
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
perl v5.18.1 2012-12-28 Net::DNS::Nameserver(3)
