lib::Net::DNS::UserlContributed Perl Dolib::Net::DNS::Resolver(3)NAMENet::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 the ENVIRONMENT
entry elsewhere in this document.
METHODS
new
$res = new Net::DNS::Resolver;
Creates a new DNS resolver object.
print
$res->print;
Prints the resolver state on the standard output.
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string
print $res->string;
Returns a string representation of the resolver state.
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.
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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.
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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 the bgsend
entry elsewhere in this document). 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.
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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.
The redundant SOA record that terminates the zone transfer
is not returned to the caller.
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.
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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.
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.
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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.
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
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# 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
the perl(1) manpage, 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, the resolver(5)
manpage, RFC 1035, RFC 1034 Section 4.3.5
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