Net::DNS::Header(3)

NAME
Net::DNS::Header - DNS packet header

SYNOPSIS
    use Net::DNS;

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

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

METHODS

  new
    $header = new Net::DNS::Header($packet);

Constructor method which returns a "Net::DNS::Header" object representing the header section of the specified packet.

  decode
        $header->decode(\$data);

Decodes the header record at the start of a DNS packet. The argument is a reference to the packet data.

  encode
        $header->encode(\$data);

Returns the header data in binary format, appropriate for use in a DNS packet.

  string
    print $packet->header->string;

Returns a 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 "answer 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 result has ", $packet->header->ad ? "" : "not", "been verified\n";

Relevant in DNSSEC context.

(The AD bit is only set on answers 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";

Gets 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->edns->size;
    $udp_max = $packet->header->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)1997-2002 Michael Fuhr.

Portions Copyright (c)2002-2004 Chris Reinhardt.

Portions Copyright (c)2012 Dick Franks.

All rights reserved.

This program is free software; you may redistribute it and/or modify it under the same terms as Perl itself.

SEE ALSO
perl, Net::DNS, Net::DNS::Packet, Net::DNS::RR::OPT RFC 1035 Section 4.1.1