dns(n) Domain Name Service dns(n) 







dns - Tcl Domain Name Service Client








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












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.









  
::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.







  

  
Specify an alternative name server for this request.

  

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

  

  
Specify an alternative port.

  
  

  

  
Override the default timeout.

  

  
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.

  

  
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.

  

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

  

  
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.







  

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

  

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

  

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

  

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

  

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

  

  
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.










% 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










  
[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)










Pat Thoyts








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.








resolver(5)








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








Networking








Copyright (c) 2002, Pat Thoyts








  

    1.3.3
    dns