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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.



Mockapetris                                                    [Page 11]
<HR>
<A href="rfc1035.html">RFC 1035</A>        Domain Implementation and Specification    November 1987


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.

3.2.2. TYPE values

TYPE fields are used in resource records.  Note that these types are a
subset of QTYPEs.

TYPE            value and meaning

A               1 a host address

NS              2 an authoritative name server

MD              3 a mail destination (Obsolete - use MX)

MF              4 a mail forwarder (Obsolete - use MX)

CNAME           5 the canonical name for an alias

SOA             6 marks the start of a zone of authority

MB              7 a mailbox domain name (EXPERIMENTAL)

MG              8 a mail group member (EXPERIMENTAL)

MR              9 a mail rename domain name (EXPERIMENTAL)

NULL            10 a null RR (EXPERIMENTAL)

WKS             11 a well known service description

PTR             12 a domain name pointer

HINFO           13 host information

MINFO           14 mailbox or mail list information

MX              15 mail exchange

TXT             16 text strings

3.2.3. QTYPE values

QTYPE fields appear in the question part of a query.  QTYPES are a
superset of TYPEs, hence all TYPEs are valid QTYPEs.  In addition, the
following QTYPEs are defined:



Mockapetris                                                    [Page 12]
<HR>
<A href="rfc1035.html">RFC 1035</A>        Domain Implementation and Specification    November 1987


AXFR            252 A request for a transfer of an entire zone

MAILB           253 A request for mailbox-related records (MB, MG or MR)

MAILA           254 A request for mail agent RRs (Obsolete - see MX)

*               255 A request for all records

3.2.4. CLASS values

CLASS fields appear in resource records.  The following CLASS mnemonics
and values are defined:

IN              1 the Internet

CS              2 the CSNET class (Obsolete - used only for examples in
                some obsolete RFCs)

CH              3 the CHAOS class

HS              4 Hesiod [Dyer 87]

3.2.5. QCLASS values

QCLASS fields appear in the question section of a query.  QCLASS values
are a superset of CLASS values; every CLASS is a valid QCLASS.  In
addition to CLASS values, the following QCLASSes are defined:

*               255 any class

3.3. Standard RRs

The following RR definitions are expected to occur, at least
potentially, in all classes.  In particular, NS, SOA, CNAME, and PTR
will be used in all classes, and have the same format in all classes.
Because their RDATA format is known, all domain names in the RDATA
section of these RRs may be compressed.

&lt;domain-name&gt; is a domain name represented as a series of labels, and
terminated by a label with zero length.  &lt;character-string&gt; is a single
length octet followed by that number of characters.  &lt;character-string&gt;
is treated as binary information, and can be up to 256 characters in
length (including the length octet).








Mockapetris                                                    [Page 13]
<HR>
<A href="rfc1035.html">RFC 1035</A>        Domain Implementation and Specification    November 1987


3.3.1. CNAME RDATA format

    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
    /                     CNAME                     /
    /                                               /
    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

where:

CNAME           A &lt;domain-name&gt; which specifies the canonical or primary
                name for the owner.  The owner name is an alias.

CNAME RRs cause no additional section processing, but name servers may
choose to restart the query at the canonical name in certain cases.  See
the description of name server logic in [<A href="rfc1034.html">RFC-1034</A>] for details.

3.3.2. HINFO RDATA format

    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
    /                      CPU                      /
    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
    /                       OS                      /
    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

where:

CPU             A &lt;character-string&gt; which specifies the CPU type.

OS              A &lt;character-string&gt; which specifies the operating
                system type.

Standard values for CPU and OS can be found in [<A href="../../../../rfc.net/rfc1010.html">RFC-1010</A>].

HINFO records are used to acquire general information about a host.  The
main use is for protocols such as FTP that can use special procedures
when talking between machines or operating systems of the same type.

3.3.3. MB RDATA format (EXPERIMENTAL)

    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
    /                   MADNAME                     /
    /                                               /
    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

where:

MADNAME         A &lt;domain-name&gt; which specifies a host which has the
                specified mailbox.



Mockapetris                                                    [Page 14]
<HR>
<A href="rfc1035.html">RFC 1035</A>        Domain Implementation and Specification    November 1987


MB records cause additional section processing which looks up an A type
RRs corresponding to MADNAME.

3.3.4. MD RDATA format (Obsolete)

    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
    /                   MADNAME                     /
    /                                               /
    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

where:

MADNAME         A &lt;domain-name&gt; which specifies a host which has a mail
                agent for the domain which should be able to deliver
                mail for the domain.

MD records cause additional section processing which looks up an A type
record corresponding to MADNAME.

MD is obsolete.  See the definition of MX and [<A href="../../../../rfc.net/rfc974.html">RFC-974</A>] for details of
the new scheme.  The recommended policy for dealing with MD RRs found in
a master file is to reject them, or to convert them to MX RRs with a
preference of 0.

3.3.5. MF RDATA format (Obsolete)

    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
    /                   MADNAME                     /
    /                                               /
    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

where:

MADNAME         A &lt;domain-name&gt; which specifies a host which has a mail
                agent for the domain which will accept mail for
                forwarding to the domain.

MF records cause additional section processing which looks up an A type
record corresponding to MADNAME.

MF is obsolete.  See the definition of MX and [<A href="../../../../rfc.net/rfc974.html">RFC-974</A>] for details ofw
the new scheme.  The recommended policy for dealing with MD RRs found in
a master file is to reject them, or to convert them to MX RRs with a
preference of 10.







Mockapetris                                                    [Page 15]
<HR>
<A href="rfc1035.html">RFC 1035</A>        Domain Implementation and Specification    November 1987


3.3.6. MG RDATA format (EXPERIMENTAL)

    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
    /                   MGMNAME                     /
    /                                               /
    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

where:

MGMNAME         A &lt;domain-name&gt; which specifies a mailbox which is a
                member of the mail group specified by the domain name.

MG records cause no additional section processing.

3.3.7. MINFO RDATA format (EXPERIMENTAL)

    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
    /                    RMAILBX                    /
    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
    /                    EMAILBX                    /
    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

where:

RMAILBX         A &lt;domain-name&gt; which specifies a mailbox which is
                responsible for the mailing list or mailbox.  If this
                domain name names the root, the owner of the MINFO RR is
                responsible for itself.  Note that many existing mailing
                lists use a mailbox X-request for the RMAILBX field of
                mailing list X, e.g., Msgroup-request for Msgroup.  This
                field provides a more general mechanism.


EMAILBX         A &lt;domain-name&gt; which specifies a mailbox which is to
                receive error messages related to the mailing list or
                mailbox specified by the owner of the MINFO RR (similar
                to the ERRORS-TO: field which has been proposed).  If
                this domain name names the root, errors should be
                returned to the sender of the message.

MINFO records cause no additional section processing.  Although these
records can be associated with a simple mailbox, they are usually used
with a mailing list.








Mockapetris                                                    [Page 16]
<HR>
<A href="rfc1035.html">RFC 1035</A>        Domain Implementation and Specification    November 1987


3.3.8. MR RDATA format (EXPERIMENTAL)

    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
    /                   NEWNAME                     /
    /                                               /
    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

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