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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 resolu-tion resolution
       tion 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.name-server/what.host.com. dns://my.nameserver/what.host.com.
       server/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 proto-col protocol
              col 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 Win-dows Windows
              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


REFERENCES
       [1]    Mockapetris,  P.,  "Domain  Names  -  Concepts  and  Facilities",  RFC  1034,  November  1987.
              (http://www.ietf.org/rfc/rfc1_34.txt)

       [2]    Mockapetris, P., "Domain Names - Implementation and Specification", RFC 1035,  November  1087.
              (http://www.ietf.org/rfc/rfc1_35.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-_9.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://source -
       forge.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)