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.
- 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 = new Net::DNS::Resolver;
Creates a new DNS resolver object.
$res->print;
Prints the resolver state on the standard output.
searchlist
@searchlist = $res->searchlist;
$res->searchlist("foo.com", "bar.com", "baz.org");
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.
search
$packet = $res->search("mailhost");
$packet = $res->search("mailhost.foo.com");
$packet = $res->search("192.168.1.1");
$packet = $res->search("foo.com", "MX");
$packet = $res->search("user.passwd.foo.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.foo.com");
$packet = $res->query("192.168.1.1");
$packet = $res->query("foo.com", "MX");
$packet = $res->query("user.passwd.foo.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.foo.com");
$packet = $res->send("foo.com", "MX");
$packet = $res->send("user.passwd.foo.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.foo.com");
$socket = $res->bgsend("foo.com", "MX");
$socket = $res->bgsend("user.passwd.foo.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.
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 an IO::Socket
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
to find out if the socket is ready, or you can use vec
and the socket's fileno
method to add the socket's file descriptor to a bitmask for select
.
bgread
$packet = $res->bgread($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.
bgisready
$socket = $res->bgsend("foo.bar.com");
until ($res->bgisready($socket)) {
# do some other processing
}
$packet = $res->bgread($socket);
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("foo.com");
@zone = $res->axfr("passwd.foo.com", "HS");
Performs a zone transfer from the first nameserver listed in nameservers
. The record class can be omitted; it defaults to IN.
Returns a list of Net::DNS::RR
objects, or undef
if the zone transfer failed.
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 this is true, calls to search, query, and send will print debugging information on the standard output. The default is false.
usevc (not yet implemented)
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.
igntc (not yet implemented)
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.
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"
A space-separated list of nameservers to query.
RES_SEARCHLIST
# Bourne Shell
RES_SEARCHLIST="foo.com bar.com baz.org"
export RES_SEARCHLIST
# C Shell
setenv RES_SEARCHLIST "foo.com bar.com baz.org"
A space-separated list of domains to put in the search list.
LOCALDOMAIN
# Bourne Shell
LOCALDOMAIN=foo.com
export LOCALDOMAIN
# C Shell
setenv LOCALDOMAIN foo.com
The default domain.
RES_OPTIONS
# Bourne Shell
RES_OPTIONS="retrans:3 retry:2 debug"
export RES_OPTIONS
# C Shell
setenv RES_OPTIONS "retrans:3 retry:2 debug"
A space-separated list of resolver options to set. Options that take values are specified as option:value.
BUGS
TCP queries are not yet implemented.
Error reporting needs to be improved.
COPYRIGHT
Copyright (c) 1997 Michael Fuhr. All rights reserved. This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
SEE ALSO
perl(1), Net::DNS, Net::DNS::Packet, Net::DNS::Header, Net::DNS::Question, Net::DNS::RR, resolver(5), RFC 1035