![]() |
![]() |
![]() |
![]() |
![]() |
![]() |
use Net::DNS::Resolver;
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:
$res = new Net::DNS::Resolver;
Creates a new DNS resolver object.
$res->print;
Prints the resolver state on the standard output.
@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:
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
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
.
$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.
$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.
@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.
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 this is true, 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.
# 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 needs to be improved.
$CommentsMailTo = "perl5@dcs.ed.ac.uk"; include("../syssies_footer.inc");?>