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";

Gets the number of records in the answer section of the packet. 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";

Gets the number of records in the authority section of the packet. 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";

Gets the number of records in the additional section of the packet. 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

cpanm Net::DNS

perl -MCPAN -e shell
install Net::DNS