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Manual Reference Pages  -  NET::DNS::TOOLKIT::RR::A (3)

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



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

  Net::DNS::ToolKit::RR::A 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;

        $netaddr) = $get->A(\$buffer,$offset);

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


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


<B>Net::DNS::ToolKit::RR:AB> appends an A resource record to a DNS packet under construction, recovers an A 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.

  3.4.1. A RDATA format

    |                    ADDRESS                    |


  ADDRESS         A 32 bit Internet address.

Hosts that have multiple Internet addresses will have multiple A records.
o @stuff = $get->A(\$buffer,$offset);

  Get the contents of the resource record.

  USE: @stuff = $get->next(\$buffer,$offset);

  where: @stuff = (
  $newoff $name,$type,$class,$ttl,$rdlength,
  $netaddr );

All except the last item, <B>B>$netaddr<B>B>, is provided by the class loader, <B>Net::DNS::ToolKit::RRB>. The code in this method knows how to retrieve <B>B>$netaddr<B>B>.

  input:        pointer to buffer,
                offset into buffer
  returns:      offset to next resource,
                @common RR elements,
                packed IPv4 address
                  in network order

  NOTE: convert IPv4 address to dot quad text
        using Net::DNS::ToolKit::inet_ntoa

o ($newoff,@dnptrs)=$put->A(\$buffer,$offset,\@dnptrs,

Append an A record to $buffer.

  where @common = $name,$type,$class,$ttl

The <B>AB> method will insert the $rdlength and $netaddr, then pass through the updated pointer to the array of compressed names

The class loader, <B>Net::DNS::ToolKit::RRB>, 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,
                packed IPv4 address
                  in network order
  output:       offset to next RR,
                new compressed name pointer array,
           or   empty list () on error.

  NOTE: convert dot quad text to a packed network
        address using Net::DNS::ToolKit::inet_aton

o (@COMMON,$RDATA) = $parse->A(@common,$rdata,...);

Converts binary/numeric field data into human readable form. The common RR elements are supplied by the class loader, <B>Net::DNS::ToolKit::RRB>. This module knows how to parse its RDATA.

Common is: name,$type,$class,$ttl,$rdlength

  name       is already text.
  type       numeric to text
  class      numeric to text
  ttl        numeric to text
  rdlength   is a number
  rdata      RR specific conversion

Resource Record <B>AB> returns $rdata containing a packed IPv4 network address. The parse operation would be:


  type       1 
  class      1 
  ttl        123
  rdlength   4
  rdata      a packed IPv4 address


  type       T_A
  class      C_IN
  ttl        123 # 2m 3s
  rdlength   4






Michael Robinton <>


    Copyright 2003 - 2011, Michael Robinton <>

Michael Robinton <>

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), Net::DNS::ToolKit::RR::Template(3)


Hey! <B>The above document had some coding errors, which are explained below:B>
Around line 18: =cut found outside a pod block. Skipping to next block.
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perl v5.20.3 NET::DNS::TOOLKIT::RR::A (3) 2011-11-05

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