trusty (3) Net::DNS::Nameserver.3pm.gz
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.
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