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Net::DNS::Resolver - DNS resolver class |
Net::DNS::Resolver - DNS resolver class
use Net::DNS::Resolver;
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:
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.
$res = new Net::DNS::Resolver;
Creates a new DNS resolver object.
$res->print;
Prints the resolver state on the standard output.
print $res->string;
Returns a string representation of the resolver state.
@searchlist = $res->searchlist;
$res->searchlist("foo.com", "bar.com", "baz.org");
Gets or sets the resolver search list.
@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.
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.
$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:
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.
$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.
$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.
$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 or IO::Select
to find out if the socket is ready before reading it.
$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.
$socket = $res->bgsend("foo.bar.com");
until ($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.
@zone = $res->axfr;
@zone = $res->axfr("foo.com");
@zone = $res->axfr("passwd.foo.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.
Here's an example that uses a timeout:
$res->tcp_timeout(10);
@zone = $res->axfr("foo.com");
if (@zone) {
foreach $rr (@zone) {
$rr->print;
}
}
else {
print "Zone transfer failed: ", $res->errorstring, "\n";
}
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).
print "retrans interval: ", $res->retrans, "\n";
$res->retrans(3);
Get or set the retransmission interval. The default is 5.
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.
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.
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.
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.
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.
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.
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.
print "query status: ", $res->errorstring, "\n";
Returns a string containing the status of the most recent query.
print "last answer was from: ", $res->answerfrom, "\n";
Returns the IP address from which we received the last answer in response to a query.
print "size of last answer: ", $res->answersize, "\n";
Returns the size in bytes of the last answer we received in response to a query.
The following environment variables can also be used to configure the resolver:
# 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.
# 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.
# Bourne Shell
LOCALDOMAIN=foo.com
export LOCALDOMAIN
# C Shell
setenv LOCALDOMAIN foo.com
The default domain.
# 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.
Error reporting and handling needs to be improved.
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.
perl(1), the Net::DNS manpage, the Net::DNS::Packet manpage, the Net::DNS::Update manpage, the Net::DNS::Header manpage, the Net::DNS::Question manpage, the Net::DNS::RR manpage, resolver(5), RFC 1035, RFC 1034 Section 4.3.5
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Net::DNS::Resolver - DNS resolver class |