Michael Robinton


Net::DNS::ToolKit::RR::MX - Resource Record Handler


  DO NOT use Net::DNS::ToolKit::RR::MX
  DO NOT require Net::DNS::ToolKit::RR::MX

  Net::DNS::ToolKit::RR::MX is autoloaded by 
  class Net::DNS::ToolKit::RR and its methods
  are instantiated in a 'special' manner.

  use Net::DNS::ToolKit::RR;
  ($get,$put,$parse) = new Net::DNS::ToolKit::RR;

        $pref,$mxdname) = $get->MX(\$buffer,$offset);

  Note: the $get->MX method is normally called
  via:  @stuff = $get->next(\$buffer,$offset);


    = $parse->MX($name,$type,$class,$ttl,$rdlength,


Net::DNS::ToolKit::RR:MX appends an MX resource record to a DNS packet under construction, recovers an MX resource record from a packet being decoded, and converts the numeric/binary portions of the resource record to human readable form.

  Description from RFC1035.txt

  3.2.1. Format

  All RRs have the same top level format shown below:

                                    1  1  1  1  1  1
      0  1  2  3  4  5  6  7  8  9  0  1  2  3  4  5
    |                      NAME                     |
    |                      TYPE                     |
    |                     CLASS                     |
    |                      TTL                      |
    |                   RDLENGTH                    |
    |                     RDATA                     |

  NAME  an owner name, i.e., the name of the node to which this
        resource record pertains.

  TYPE  two octets containing one of the RR TYPE codes.

  CLASS two octets containing one of the RR CLASS codes.

  TTL   a 32 bit signed integer that specifies the time interval
        that the resource record may be cached before the source
        of the information should again be consulted.  Zero
        values are interpreted to mean that the RR can only be
        used for the transaction in progress, and should not be
        cached.  For example, SOA records are always distributed
        with a zero TTL to prohibit caching.  Zero values can
        also be used for extremely volatile data.

  RDLENGTH an unsigned 16 bit integer that specifies the length
        in octets of the RDATA field.

  RDATA a variable length string of octets that describes the
        resource.  The format of this information varies
        according to the TYPE and CLASS of the resource record.

    3.3.9. MX RDATA format

    |                  PREFERENCE                   |
    /                   EXCHANGE                    /
    /                                               /


    PREFERENCE A 16 bit integer which specifies the 
        preference given to this RR among others at the 
        same owner.  Lower values are preferred.

    EXCHANGE A <domain-name> which specifies a host willing
        to act as a mail exchange for the owner name.

MX records cause type A additional section processing for the host specified by EXCHANGE. The use of MX RRs is explained in detail in [RFC-974].

  • @stuff = $get->MX(\$buffer,$offset);

      Get the contents of the resource record.
      USE: @stuff = $get->next(\$buffer,$offset);
      where: @stuff = (
      $newoff $name,$type,$class,$ttl,$rdlength,
      $pref,$mxdname );

    All except the last two items, $pref, $mxdname, are provided by the class loader, Net::DNS::ToolKit::RR. The code in this method knows how to retrieve $pref, $mxdname.

      input:        pointer to buffer,
                    offset into buffer
      returns:      offset to next resource,
                    @common RR elements,
                    mail host domain name
  • ($newoff,@dnptrs)=$put->MX(\$buffer,$offset,\@dnptrs, $name,$type,$class,$ttl,$pref,$mxdname);

    Append an MX record to $buffer.

      where @common = (

    The method will insert the $rdlength, $pref and $mxdname, then return the updated pointer to the array of compressed names

    The class loader, Net::DNS::ToolKit::RR, inserts the @common elements and returns updated @dnptrs. This module knows how to insert its RDATA and calculate the $rdlength.

      input:        pointer to buffer,
                    offset (normally end of buffer), 
                    pointer to compressed name array,
                    @common RR elements,
                    mail host domain name
      output:       offset to next RR,
                    new compressed name pointer array,
               or   empty list () on error.
  • (@COMMON,$pref,$MXDNAME) = $parse->MX(@common,$pref,$mxdname);

    Converts binary/numeric field data into human readable form. The common RR elements are supplied by the class loader, Net::DNS::ToolKit::RR. For MX RR's, this returns $mxdname terminated with '.'

      input:        preference,
                    MX Domain Name
      returns:      preference
                    MX Domain Name.






Michael Robinton <michael@bizsystems.com>


    Copyright 2003 - 2011, Michael Robinton <michael@bizsystems.com>

Michael Robinton <michael@bizsystems.com>

All rights reserved.

This program is free software; you can redistribute it and/or modify it under the terms of either:

  a) the GNU General Public License as published by the Free
  Software Foundation; either version 2, or (at your option) any
  later version, or

  b) the "Artistic License" which comes with this distribution.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See either the GNU General Public License or the Artistic License for more details.

You should have received a copy of the Artistic License with this distribution, in the file named "Artistic". If not, I'll be glad to provide one.

You should also have received a copy of the GNU General Public License along with this program in the file named "Copying". If not, write to the

        Free Software Foundation, Inc.                        
        59 Temple Place, Suite 330
        Boston, MA  02111-1307, USA                                     

or visit their web page on the internet at:


See also:

Net::DNS::Codes(3), Net::DNS::ToolKit(3)