# dns(n) 1.0.1 dns "dns"

## NAME

dns - Tcl Domain Name Service Client

## SYNOPSIS

package require Tcl 8.2
package require dns ?1.0.1?

::dns::resolve query ?options?
::dns::configure ?options?
::dns::name token
::dns::address token
::dns::cname token
::dns::status token
::dns::error token
::dns::reset token
::dns::wait token
::dns::cleanup token

## DESCRIPTION

The dns package provides a Tcl only Domain Name Service client. You should refer to RFC 1034 and RFC 1035 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. The package also extends the package uri to support DNS URIs or 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: This package uses TCP to query DNS servers as the tcl core does not implement UDP networking. This means that this module will not work if DNS over TCP is blocked by a firewall, or not accepted by the chosen nameserver.

## 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. However only tcp is currently implemented in the package.
  -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, AXFR, MAILB, MAILA and *. See RFC1035 for details about the return values.
  -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. Defaults to 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. Defaults to 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::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.

## 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

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"]

## SEE ALSO

resolver(5)

## AUTHORS

Pat Thoyts

## KEYWORDS

DNS, resolver, domain name service