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ActiveTcl User Guide
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dns(n) 1.2.0 "dns"
dns - Tcl Domain Name Service Client
TABLE OF
CONTENTS
SYNOPSIS
DESCRIPTION
COMMANDS
EXAMPLES
REFERENCES
AUTHORS
SEE ALSO
KEYWORDS
COPYRIGHT
package require Tcl 8.2
package require dns ?1.2.1?
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.
- -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.
- ::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.
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% 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
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Using DNS URIs as queries:
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% set tok [dns::resolve "dns:tcl.tk;type=MX"]
% set tok [dns::resolve "dns://l.root-servers.net/www.tcl.tk"]
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Reverse address lookup:
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% set tok [dns::resolve 127.0.0.1]
::dns::1
% dns::name $tok
localhost
% dns::cleanup $tok
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- Mockapetris, P., "Domain Names - Concepts and Facilities", RFC
1034, November 1987. (http://www.ietf.org/rfc/rfc1034.txt)
- Mockapetris, P., "Domain Names - Implementation and
Specification", RFC 1035, November 1087. (http://www.ietf.org/rfc/rfc1035.txt)
- Thompson, S. and Huitema, C., "DNS Extensions to support IP
version 6", RFC 1886, December 1995. (http://www.ietf.org/rfc/rfc1886.txt)
- Josefsson, S., "Domain Name System Uniform Resource
Identifiers", Internet-Draft, October 2003, (
http://www.ietf.org/internet-drafts/draft-josefsson-dns-url-09.txt)
- 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)
Pat Thoyts
resolver(5)
DNS , domain name service , resolver , rfc 1034 , rfc 1035 , rfc 1886
Copyright © 2002, Pat Thoyts