NAME

Net::DNS::Resolver - DNS resolver class

SYNOPSIS

use Net::DNS::Resolver;

DESCRIPTION

Instances of the Net::DNS::Resolver class represent resolver objects. A program can have multiple resolver objects, each maintaining its own state information such as the nameservers to be queried, whether recursion is desired, etc.

Resolver configuration is read from the following files, in the order indicated:

/etc/resolv.conf
$HOME/.resolv.conf
./.resolv.conf

The following keywords are recognized in resolver configuration files:

domain

The default domain.

search

A space-separated list of domains to put in the search list.

item nameserver

A space-separated list of nameservers to query.

Files except for /etc/resolv.conf must be owned by the effective userid running the program or they won't be read. In addition, several environment variables can also contain configuration information; see "ENVIRONMENT".

METHODS

new

$res = Net::DNS::Resolver->new;

Creates a new DNS resolver object.

print

$res->print;

Prints the resolver state on the standard output.

string

print $res->string;

Returns a string representation of the resolver state.

searchlist

@searchlist = $res->searchlist;
$res->searchlist('example.com', 'sub1.example.com', 'sub2.example.com');

Gets or sets the resolver search list.

nameservers

@nameservers = $res->nameservers;
$res->nameservers('192.168.1.1', '192.168.2.2', '192.168.3.3');

Gets or sets the nameservers to be queried.

port

print 'sending queries to port ', $res->port, "\n";
$res->port(9732);

Gets or sets the port to which we send queries. This can be useful for testing a nameserver running on a non-standard port. The default is port 53.

srcport

print 'sending queries from port ', $res->srcport, "\n";
$res->srcport(5353);

Gets or sets the port from which we send queries. The default is 0, meaning any port.

srcaddr

print 'sending queries from address ', $res->srcaddr, "\n";
$res->srcaddr('192.168.1.1');

Gets or sets the source address from which we send queries. Convenient for forcing queries out a specific interfaces on a multi-homed host. The default is 0.0.0.0, meaning any local address.

search

$packet = $res->search('mailhost');
$packet = $res->search('mailhost.example.com');
$packet = $res->search('192.168.1.1');
$packet = $res->search('example.com', 'MX');
$packet = $res->search('user.passwd.example.com', 'TXT', 'HS');

Performs a DNS query for the given name, applying the searchlist if appropriate. The search algorithm is as follows:

If the name contains at least one dot, try it as is.
If the name doesn't end in a dot then append each item in the search list to the name. This is only done if dnsrch is true.
If the name doesn't contain any dots, try it as is.

The record type and class can be omitted; they default to A and IN. If the name looks like an IP address (4 dot-separated numbers), then an appropriate PTR query will be performed.

Returns a Net::DNS::Packet object, or undef if no answers were found.

query

$packet = $res->query('mailhost');
$packet = $res->query('mailhost.example.com');
$packet = $res->query('192.168.1.1');
$packet = $res->query('example.com', 'MX');
$packet = $res->query('user.passwd.example.com', 'TXT', 'HS');

Performs a DNS query for the given name; the search list is not applied. If the name doesn't contain any dots and defnames is true then the default domain will be appended.

The record type and class can be omitted; they default to A and IN. If the name looks like an IP address (4 dot-separated numbers), then an appropriate PTR query will be performed.

Returns a Net::DNS::Packet object, or undef if no answers were found.

send

$packet = $res->send($packet_object);
$packet = $res->send('mailhost.example.com');
$packet = $res->send('example.com', 'MX');
$packet = $res->send('user.passwd.example.com', 'TXT', 'HS');

Performs a DNS query for the given name. Neither the searchlist nor the default domain will be appended.

The argument list can be either a Net::DNS::Packet object or a list of strings. The record type and class can be omitted; they default to A and IN. If the name looks like an IP address (4 dot-separated numbers), then an appropriate PTR query will be performed.

Returns a Net::DNS::Packet object whether there were any answers or not. Use $packet->header->ancount or $packet->answer to find out if there were any records in the answer section. Returns undef if there was an error.

bgsend

$socket = $res->bgsend($packet_object);
$socket = $res->bgsend('mailhost.example.com');
$socket = $res->bgsend('example.com', 'MX');
$socket = $res->bgsend('user.passwd.example.com', 'TXT', 'HS');

Performs a background DNS query for the given name, i.e., sends a query packet to the first nameserver listed in $res->nameservers and returns immediately without waiting for a response. The program can then perform other tasks while waiting for a response from the nameserver.

Returns an IO::Socket::INET object. The program must determine when the socket is ready for reading and call $res->bgread to get the response packet. You can use $res->bgisready or IO::Select to find out if the socket is ready before reading it.

bgread

$packet = $res->bgread($socket);
undef $socket;

Reads the answer from a background query (see "bgsend"). The argument is an IO::Socket object returned by bgsend.

Returns a Net::DNS::Packet object or undef on error.

The programmer should close or destroy the socket object after reading it.

bgisready

    $socket = $res->bgsend('foo.example.com');
    until ($res->bgisready($socket)) {
	# do some other processing
    }
    $packet = $res->bgread($socket);
    $socket = undef;

Determines whether a socket is ready for reading. The argument is an IO::Socket object returned by $res->bgsend.

Returns true if the socket is ready, false if not.

axfr

@zone = $res->axfr;
@zone = $res->axfr('example.com');
@zone = $res->axfr('passwd.example.com', 'HS');

Performs a zone transfer from the first nameserver listed in nameservers. If the zone is omitted, it defaults to the first zone listed in the resolver's search list. If the class is omitted, it defaults to IN.

Returns a list of Net::DNS::RR objects, or undef if the zone transfer failed.

The redundant SOA record that terminates the zone transfer is not returned to the caller.

axfr_start

$res->axfr_start;
$res->axfr_start('example.com');
$res->axfr_start('example.com', 'HS');

Starts a zone transfer from the first nameserver listed in nameservers. If the zone is omitted, it defaults to the first zone listed in the resolver's search list. If the class is omitted, it defaults to IN.

Returns the IO::Socket::INET object that will be used for reading, or undef on error.

Use axfr_next to read the zone records one at a time.

axfr_next

    $res->axfr_start('example.com');
    while ($rr = $res->axfr_next) {
	$rr->print;
    }

Reads records from a zone transfer one at a time.

Returns undef at the end of the zone transfer. The redundant SOA record that terminates the zone transfer is not returned.

tsig

$tsig = $res->tsig;

$res->tsig(Net::DNS::RR->new("$key_name TSIG $key"));

$tsig = Net::DNS::RR->new("$key_name TSIG $key");
$tsig->fudge(60);
$res->tsig($tsig);

$res->tsig($key_name, $key);

$res->tsig(0);

Get or set the TSIG record used to automatically sign outgoing queries and updates. Call with an argument of 0 or '' to turn off automatic signing.

The default resolver behavior is not to sign any packets. You must call this method to set the key if you'd like the resolver to sign packets automatically.

You can also sign packets manually -- see the Net::DNS::Packet and Net::DNS::Update manual pages for examples. TSIG records in manually-signed packets take precedence over those that the resolver would add automatically.

retrans

print 'retrans interval: ', $res->retrans, "\n";
$res->retrans(3);

Get or set the retransmission interval. The default is 5.

retry

print 'number of tries: ', $res->retry, "\n";
$res->retry(2);

Get or set the number of times to try the query. The default is 4.

recurse

print 'recursion flag: ', $res->recurse, "\n";
$res->recurse(0);

Get or set the recursion flag. If this is true, nameservers will be requested to perform a recursive query. The default is true.

defnames

print 'defnames flag: ', $res->defnames, "\n";
$res->defnames(0);

Get or set the defnames flag. If this is true, calls to query will append the default domain to names that contain no dots. The default is true.

dnsrch

print 'dnsrch flag: ', $res->dnsrch, "\n";
$res->dnsrch(0);

Get or set the dnsrch flag. If this is true, calls to search will apply the search list. The default is true.

debug

print 'debug flag: ', $res->debug, "\n";
$res->debug(1);

Get or set the debug flag. If set, calls to search, query, and send will print debugging information on the standard output. The default is false.

usevc

print 'usevc flag: ', $res->usevc, "\n";
$res->usevc(1);

Get or set the usevc flag. If true, then queries will be performed using virtual circuits (TCP) instead of datagrams (UDP). The default is false.

tcp_timeout

print 'TCP timeout: ', $res->tcp_timeout, "\n";
$res->tcp_timeout(10);

Get or set the TCP timeout in seconds. A timeout of undef means indefinite. The default is 120 seconds (2 minutes).

persistent_tcp

print 'Persistent TCP flag: ', $res->persistent_tcp, "\n";
$res->persistent_tcp(1);

Get or set the persistent TCP setting. If set to true, Net::DNS will keep a TCP socket open for each host:port to which it connects. This is useful if you're using TCP and need to make a lot of queries or updates to the same nameserver.

This option defaults to false unless you're running under a SOCKSified Perl, in which case it defaults to true.

igntc

print 'igntc flag: ', $res->igntc, "\n";
$res->igntc(1);

Get or set the igntc flag. If true, truncated packets will be ignored. If false, truncated packets will cause the query to be retried using TCP. The default is false.

errorstring

print 'query status: ', $res->errorstring, "\n";

Returns a string containing the status of the most recent query.

answerfrom

print 'last answer was from: ', $res->answerfrom, "\n";

Returns the IP address from which we received the last answer in response to a query.

answersize

print 'size of last answer: ', $res->answersize, "\n";

Returns the size in bytes of the last answer we received in response to a query.

dnssec

print "dnssec flag: ", $res->dnssec, "\n";
$res->dnssec(0);

Enabled DNSSEC this will set the checking disabled flag in the query header and add EDNS0 data as in RFC2671 and RFC3225

When set to true the answer and additional section of queries from secured zones will contain KEY, NXT and SIG records.

cdflag

print "checking disabled flag: ", $res->dnssec, "\n";
$res->dnssec(1);
$res->cdflag(1);

Sets or gets the CD bit for a dnssec query. This bit is always zero for non dnssec queries. When the dnssec is enabled the flag can be set to 1.

udppacketsize

print "udppacketsize: ", $res->udppacketsize, "\n";
$res->udppacketsize(2048);

udppacketsize will set or get the packet size. If set to a value greater than &Net::DNS::PACKETSZ an EDNS extention will be added indicating suppport for MTU path recovery.

Default udppacketsize is &Net::DNS::PACKETSZ (512)

ENVIRONMENT

The following environment variables can also be used to configure the resolver:

RES_NAMESERVERS

# Bourne Shell
RES_NAMESERVERS="192.168.1.1 192.168.2.2 192.168.3.3"
export RES_NAMESERVERS

# C Shell
setenv RES_NAMESERVERS "192.168.1.1 192.168.2.2 192.168.3.3"