NAME

       Net::DNS::Header - DNS packet header

SYNOPSIS

           use Net::DNS;

           $packet = Net::DNS::Packet->new();
           $header = $packet->header;

DESCRIPTION

       "Net::DNS::Header" represents the header portion of a DNS packet.

METHODS

   $packet->header
           $packet = Net::DNS::Packet->new();
           $header = $packet->header;

       Net::DNS::Header objects emanate from the Net::DNS::Packet header() method, and contain an
       opaque reference to the parent Packet object.

       Header objects may be assigned to suitably scoped lexical variables.  They should never be
       stored in global variables or persistent data structures.

   string
           print $packet->header->string;

       Returns a string representation of the packet header.

   print
           $packet->header->print;

       Prints the string representation of the packet header.

   id
           print "query id = ", $packet->header->id, "\n";
           $packet->header->id(1234);

       Gets or sets the query identification number.

       A random value is assigned if the argument value is undefined.

   opcode
           print "query opcode = ", $packet->header->opcode, "\n";
           $packet->header->opcode("UPDATE");

       Gets or sets the query opcode (the purpose of the query).

   rcode
           print "query response code = ", $packet->header->rcode, "\n";
           $packet->header->rcode("SERVFAIL");

       Gets or sets the query response code (the status of the query).

   qr
           print "query response flag = ", $packet->header->qr, "\n";
           $packet->header->qr(0);

       Gets or sets the query response flag.

   aa
           print "response is ", $packet->header->aa ? "" : "non-", "authoritative\n";
           $packet->header->aa(0);

       Gets or sets the authoritative answer flag.

   tc
           print "packet is ", $packet->header->tc ? "" : "not ", "truncated\n";
           $packet->header->tc(0);

       Gets or sets the truncated packet flag.

   rd
           print "recursion was ", $packet->header->rd ? "" : "not ", "desired\n";
           $packet->header->rd(0);

       Gets or sets the recursion desired flag.

   ra
           print "recursion is ", $packet->header->ra ? "" : "not ", "available\n";
           $packet->header->ra(0);

       Gets or sets the recursion available flag.

   z
       Unassigned bit, should always be zero.

   ad
           print "The response has ", $packet->header->ad ? "" : "not", "been verified\n";

       Relevant in DNSSEC context.

       (The AD bit is only set on a response where signatures have been cryptographically
       verified or the server is authoritative for the data and is allowed to set the bit by
       policy.)

   cd
           print "checking was ", $packet->header->cd ? "not" : "", "desired\n";
           $packet->header->cd(0);

       Gets or sets the checking disabled flag.

   qdcount, zocount
           print "# of question records: ", $packet->header->qdcount, "\n";

       Returns the number of records in the question section of the packet.  In dynamic update
       packets, this field is known as "zocount" and refers to the number of RRs in the zone
       section.

   ancount, prcount
           print "# of answer records: ", $packet->header->ancount, "\n";

       Returns the number of records in the answer section of the packet which may, in the case
       of corrupt packets, differ from the actual number of records.  In dynamic update packets,
       this field is known as "prcount" and refers to the number of RRs in the prerequisite
       section.

   nscount, upcount
           print "# of authority records: ", $packet->header->nscount, "\n";

       Returns the number of records in the authority section of the packet which may, in the
       case of corrupt packets, differ from the actual number of records.  In dynamic update
       packets, this field is known as "upcount" and refers to the number of RRs in the update
       section.

   arcount, adcount
           print "# of additional records: ", $packet->header->arcount, "\n";

       Returns the number of records in the additional section of the packet which may, in the
       case of corrupt packets, differ from the actual number of records.  In dynamic update
       packets, this field is known as "adcount".

EDNS Protocol Extensions

   do
           print "DNSSEC_OK flag was ", $packet->header->do ? "not" : "", "set\n";
           $packet->header->do(1);

       Gets or sets the EDNS DNSSEC OK flag.

   Extended rcode
       EDNS extended rcodes are handled transparently by $packet->header->rcode().

   UDP packet size
           $udp_max = $packet->header->size;
           $udp_max = $packet->edns->size;

       EDNS offers a mechanism to advertise the maximum UDP packet size which can be assembled by
       the local network stack.

       UDP size advertisement can be viewed as either a header extension or an EDNS feature.
       Endless debate is avoided by supporting both views.

   edns
           $header  = $packet->header;
           $version = $header->edns->version;
           @options = $header->edns->options;
           $option  = $header->edns->option(n);
           $udp_max = $packet->edns->size;

       Auxiliary function which provides access to the EDNS protocol extension OPT RR.

COPYRIGHT

       Copyright (c)1997 Michael Fuhr.

       Portions Copyright (c)2002,2003 Chris Reinhardt.

       Portions Copyright (c)2012,2022 Dick Franks.

       All rights reserved.

LICENSE

       Permission to use, copy, modify, and distribute this software and its documentation for
       any purpose and without fee is hereby granted, provided that the original copyright
       notices appear in all copies and that both copyright notice and this permission notice
       appear in supporting documentation, and that the name of the author not be used in
       advertising or publicity pertaining to distribution of the software without specific prior
       written permission.

       THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
       INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
       PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE
       FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
       OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
       DEALINGS IN THE SOFTWARE.

SEE ALSO

       perl, Net::DNS, Net::DNS::Packet, Net::DNS::RR::OPT, RFC1035(4.1.1)
       <https://tools.ietf.org/html/rfc1035>