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
);
Returns a Net::DNS::Nameserver object, or undef if the object could not be
created.
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 available in VERSION > 830. Only UDP
replies are truncated. The size limit is determined by the advertised EDNS0
size 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). 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