


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  sys-
       tems.  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



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dns(n)                 Domain Name Service                 dns(n)


       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 qual-
              ified 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 recur-
                     sively 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



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dns(n)                 Domain Name Service                 dns(n)


              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 pack-
                     age 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






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dns(n)                 Domain Name Service                 dns(n)


       ::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 com-
              pletion.


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


       ::dns::nameservers
              Attempts to return a list of the nameservers  currently  config-
              ured  for  the  users  system. On a unix machine this parses the
              /etc/resolv.conf file for nameservers (if it exists) and on Win-
              dows  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




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dns(n)                 Domain Name Service                 dns(n)


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  Specifica-
              tion",          RFC         1035,         November         1087.
              (http://www.ietf.org/rfc/rfc1035.txt)

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

       [4]    Josefsson, S., "Domain  Name  System  Uniform  Resource  Identi-
              fiers",          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 speci-
              fying 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











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