dns(n)                        Domain Name Service                       dns(n)



______________________________________________________________________________

NAME
       dns - Tcl Domain Name Service Client

SYNOPSIS
       package require Tcl  8.2

       package require dns  ?1.3.3?

       ::dns::resolve query ?options?

       ::dns::configure ?options?

       ::dns::name token

       ::dns::address token

       ::dns::cname token

       ::dns::result token

       ::dns::status token

       ::dns::error token

       ::dns::reset token

       ::dns::wait token

       ::dns::cleanup token

       ::dns::nameservers

_________________________________________________________________

DESCRIPTION
       The dns package provides a Tcl only Domain Name Service client. You
       should refer to (1) and (2) for information about the DNS protocol or
       read resolver(3) to find out how the C library resolves domain names.
       The intention of this package is to insulate Tcl scripts from problems
       with using the system library resolver for slow name servers.  It may
       or may not be of practical use. Internet name resolution is a complex
       business and DNS is only one part of the resolver. You may find you are
       supposed to be using hosts files, NIS or WINS to name a few other
       systems. This package is not a substitute for the C library resolver -
       it does however implement name resolution over DNS.  The package also
       extends the package uri to support DNS URIs (4) of the form
       dns:what.host.com or dns://my.nameserver/what.host.com. The
       dns::resolve command can handle DNS URIs or simple domain names as a
       query.

       Note: The package defaults to using DNS over TCP connections. If you
       wish to use UDP you will need to have the tcludp package installed and
       have a version that correctly handles binary data (> 1.0.4).  This is
       available at http://tcludp.sourceforge.net/.  If the udp package is
       present then UDP will be used by default.

COMMANDS
       ::dns::resolve query ?options?
              Resolve a domain name using the DNS protocol. query is the
              domain name to be lookup up. This should be either a fully
              qualified domain name or a DNS URI.

              -nameserver hostname or -server hostname
                     Specify an alternative name server for this request.

              -protocol tcp|udp
                     Specify the network protocol to use for this request. Can
                     be one of tcp or udp.

              -port portnum
                     Specify an alternative port.

              -search domainlist

              -timeout milliseconds
                     Override the default timeout.

              -type TYPE
                     Specify the type of DNS record you are interested in.
                     Valid values are A, NS, MD, MF, CNAME, SOA, MB, MG, MR,
                     NULL, WKS, PTR, HINFO, MINFO, MX, TXT, SPF, SRV, AAAA,
                     AXFR, MAILB, MAILA and *.  See RFC1035 for details about
                     the return values.  See http://spf.pobox.com/ about SPF.
                     See (3) about AAAA records and RFC2782 for details of SRV
                     records.

              -class CLASS
                     Specify the class of domain name. This is usually IN but
                     may be one of IN for internet domain names, CS, CH, HS or
                     * for any class.

              -recurse boolean
                     Set to false if you do not want the name server to
                     recursively act upon your request. Normally set to true.

              -command procname
                     Set a procedure to be called upon request completion. The
                     procedure will be passed the token as its only argument.


       ::dns::configure ?options?
              The ::dns::configure command is used to setup the dns package.
              The server to query, the protocol and domain search path are all
              set via this command. If no arguments are provided then a list
              of all the current settings is returned.  If only one argument
              then it must the the name of an option and the value for that
              option is returned.

              -nameserver hostname
                     Set the default name server to be used by all queries.
                     The default is localhost.

              -protocol tcp|udp
                     Set the default network protocol to be used. Default is
                     tcp.

              -port portnum
                     Set the default port to use on the name server. The
                     default is 53.

              -search domainlist
                     Set the domain search list. This is currently not used.

              -timeout milliseconds
                     Set the default timeout value for DNS lookups. Default is
                     30 seconds.

              -loglevel level
                     Set the log level used for emitting diagnostic messages
                     from this package. The default is warn. See the log
                     package for details of the available levels.


       ::dns::name token
              Returns a list of all domain names returned as an answer to your
              query.


       ::dns::address token
              Returns a list of the address records that match your query.


       ::dns::cname token
              Returns a list of canonical names (usually just one) matching
              your query.


       ::dns::result token
              Returns a list of all the decoded answer records provided for
              your query. This permits you to extract the result for more
              unusual query types.


       ::dns::status token
              Returns the status flag. For a successfully completed query this
              will be ok. May be error or timeout or eof.  See also
              ::dns::error


       ::dns::error token
              Returns the error message provided for requests whose status is
              error.  If there is no error message then an empty string is
              returned.


       ::dns::reset token
              Reset or cancel a DNS query.


       ::dns::wait token
              Wait for a DNS query to complete and return the status upon
              completion.


       ::dns::cleanup token
              Remove all state variables associated with the request.


       ::dns::nameservers
              Attempts to return a list of the nameservers currently
              configured for the users system. On a unix machine this parses
              the /etc/resolv.conf file for nameservers (if it exists) and on
              Windows systems we examine certain parts of the registry. If no
              nameserver can be found then the loopback address (127.0.0.1) is
              used as a default.

EXAMPLES
              % set tok [dns::resolve www.tcl.tk]
              ::dns::1
              % dns::status $tok
              ok
              % dns::address $tok
              199.175.6.239
              % dns::name $tok
              www.tcl.tk
              % dns::cleanup $tok


       Using DNS URIs as queries:


              % set tok [dns::resolve "dns:tcl.tk;type=MX"]
              % set tok [dns::resolve "dns://l.root-servers.net/www.tcl.tk"]


       Reverse address lookup:


              % set tok [dns::resolve 127.0.0.1]
              ::dns::1
              % dns::name $tok
              localhost
              % dns::cleanup $tok


REFERENCES
       [1]    Mockapetris, P., "Domain Names - Concepts and Facilities", RFC
              1034, November 1987.  (http://www.ietf.org/rfc/rfc1034.txt)

       [2]    Mockapetris, P., "Domain Names - Implementation and
              Specification", RFC 1035, November 1087.
              (http://www.ietf.org/rfc/rfc1035.txt)

       [3]    Thompson, S. and Huitema, C., "DNS Extensions to support IP
              version 6", RFC 1886, December 1995.
              (http://www.ietf.org/rfc/rfc1886.txt)

       [4]    Josefsson, S., "Domain Name System Uniform Resource
              Identifiers", Internet-Draft, October 2003,
              (http://www.ietf.org/internet-drafts/draft-josefsson-dns-
              url-09.txt)

       [5]    Gulbrandsen, A., Vixie, P. and Esibov, L., "A DNS RR for
              specifying the location of services (DNS SRV)", RFC 2782,
              February 2000, (http://www.ietf.org/rfc/rfc2782.txt)

       [6]    Ohta, M. "Incremental Zone Transfer in DNS", RFC 1995, August
              1996, (http://www.ietf.org/rfc/rfc1995.txt)

AUTHORS
       Pat Thoyts

BUGS, IDEAS, FEEDBACK
       This document, and the package it describes, will undoubtedly contain
       bugs and other problems.  Please report such in the category dns of the
       Tcllib SF Trackers [http://sourceforge.net/tracker/?group_id=12883].
       Please also report any ideas for enhancements you may have for either
       package and/or documentation.

SEE ALSO
       resolver(5)

KEYWORDS
       DNS, domain name service, resolver, rfc 1034, rfc 1035, rfc 1886

CATEGORY
       Networking

COPYRIGHT
       Copyright (c) 2002, Pat Thoyts




dns                                  1.3.3                              dns(n)
