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9 non-PAUSE users.

Michael Fuhr

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.

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.

print

    $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:

  1. If the name contains at least one dot, try it as is.

  2. 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.

  3. 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 set, 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