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: The default domain. A space-separated list of domains to put in the search list. 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.

new
$res = new Net::DNS::Resolver; Creates a new DNS resolver object.

print
$res->print; Prints the resolver state on the standard output.

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: 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' or `IO::Select' to find out if the socket is ready before reading it.

bgread
$packet = $res->bgread($socket); undef $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. The programmer should close or destroy the socket object after reading it.

bgisready
$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.

axfr
@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"; }

tcp_timeout
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).

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
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
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.

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. 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. 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