rfc1034.html

this gives details of the network programming

                May optionally carry the SOA RR for the authoritative
                data in the answer section.

Additional      Carries RRs which may be helpful in using the RRs in the
                other sections.

Note that the content, but not the format, of these sections varies with
header opcode.

3.7.1. Standard queries

A standard query specifies a target domain name (QNAME), query type
(QTYPE), and query class (QCLASS) and asks for RRs which match.  This
type of query makes up such a vast majority of DNS queries that we use
the term "query" to mean standard query unless otherwise specified.  The
QTYPE and QCLASS fields are each 16 bits long, and are a superset of
defined types and classes.





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The QTYPE field may contain:

&lt;any type&gt;      matches just that type. (e.g., A, PTR).

AXFR            special zone transfer QTYPE.

MAILB           matches all mail box related RRs (e.g. MB and MG).

*               matches all RR types.

The QCLASS field may contain:

&lt;any class&gt;     matches just that class (e.g., IN, CH).

*               matches aLL RR classes.

Using the query domain name, QTYPE, and QCLASS, the name server looks
for matching RRs.  In addition to relevant records, the name server may
return RRs that point toward a name server that has the desired
information or RRs that are expected to be useful in interpreting the
relevant RRs.  For example, a name server that doesn't have the
requested information may know a name server that does; a name server
that returns a domain name in a relevant RR may also return the RR that
binds that domain name to an address.

For example, a mailer tying to send mail to [e-mail] might
ask the resolver for mail information about ISI.EDU, resulting in a
query for QNAME=ISI.EDU, QTYPE=MX, QCLASS=IN.  The response's answer
section would be:

    ISI.EDU.        MX      10 VENERA.ISI.EDU.
                    MX      10 VAXA.ISI.EDU.

while the additional section might be:

    VAXA.ISI.EDU.   A       10.2.0.27
                    A       128.9.0.33
    VENERA.ISI.EDU. A       10.1.0.52
                    A       128.9.0.32

Because the server assumes that if the requester wants mail exchange
information, it will probably want the addresses of the mail exchanges
soon afterward.

Note that the QCLASS=* construct requires special interpretation
regarding authority.  Since a particular name server may not know all of
the classes available in the domain system, it can never know if it is
authoritative for all classes.  Hence responses to QCLASS=* queries can



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never be authoritative.

3.7.2. Inverse queries (Optional)

Name servers may also support inverse queries that map a particular
resource to a domain name or domain names that have that resource.  For
example, while a standard query might map a domain name to a SOA RR, the
corresponding inverse query might map the SOA RR back to the domain
name.

Implementation of this service is optional in a name server, but all
name servers must at least be able to understand an inverse query
message and return a not-implemented error response.

The domain system cannot guarantee the completeness or uniqueness of
inverse queries because the domain system is organized by domain name
rather than by host address or any other resource type.  Inverse queries
are primarily useful for debugging and database maintenance activities.

Inverse queries may not return the proper TTL, and do not indicate cases
where the identified RR is one of a set (for example, one address for a
host having multiple addresses).  Therefore, the RRs returned in inverse
queries should never be cached.

Inverse queries are NOT an acceptable method for mapping host addresses
to host names; use the IN-ADDR.ARPA domain instead.

A detailed discussion of inverse queries is contained in [<A href="rfc1035.html">RFC-1035</A>].

3.8. Status queries (Experimental)

To be defined.

3.9. Completion queries (Obsolete)

The optional completion services described in RFCs 882 and 883 have been
deleted.  Redesigned services may become available in the future, or the
opcodes may be reclaimed for other use.

4. NAME SERVERS

4.1. Introduction

Name servers are the repositories of information that make up the domain
database.  The database is divided up into sections called zones, which
are distributed among the name servers.  While name servers can have
several optional functions and sources of data, the essential task of a
name server is to answer queries using data in its zones.  By design,



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name servers can answer queries in a simple manner; the response can
always be generated using only local data, and either contains the
answer to the question or a referral to other name servers "closer" to
the desired information.

A given zone will be available from several name servers to insure its
availability in spite of host or communication link failure.  By
administrative fiat, we require every zone to be available on at least
two servers, and many zones have more redundancy than that.

A given name server will typically support one or more zones, but this
gives it authoritative information about only a small section of the
domain tree.  It may also have some cached non-authoritative data about
other parts of the tree.  The name server marks its responses to queries
so that the requester can tell whether the response comes from
authoritative data or not.

4.2. How the database is divided into zones

The domain database is partitioned in two ways: by class, and by "cuts"
made in the name space between nodes.

The class partition is simple.  The database for any class is organized,
delegated, and maintained separately from all other classes.  Since, by
convention, the name spaces are the same for all classes, the separate
classes can be thought of as an array of parallel namespace trees.  Note
that the data attached to nodes will be different for these different
parallel classes.  The most common reasons for creating a new class are
the necessity for a new data format for existing types or a desire for a
separately managed version of the existing name space.

Within a class, "cuts" in the name space can be made between any two
adjacent nodes.  After all cuts are made, each group of connected name
space is a separate zone.  The zone is said to be authoritative for all
names in the connected region.  Note that the "cuts" in the name space
may be in different places for different classes, the name servers may
be different, etc.

These rules mean that every zone has at least one node, and hence domain
name, for which it is authoritative, and all of the nodes in a
particular zone are connected.  Given, the tree structure, every zone
has a highest node which is closer to the root than any other node in
the zone.  The name of this node is often used to identify the zone.

It would be possible, though not particularly useful, to partition the
name space so that each domain name was in a separate zone or so that
all nodes were in a single zone.  Instead, the database is partitioned
at points where a particular organization wants to take over control of



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a subtree.  Once an organization controls its own zone it can
unilaterally change the data in the zone, grow new tree sections
connected to the zone, delete existing nodes, or delegate new subzones
under its zone.

If the organization has substructure, it may want to make further
internal partitions to achieve nested delegations of name space control.
In some cases, such divisions are made purely to make database
maintenance more convenient.

4.2.1. Technical considerations

The data that describes a zone has four major parts:

   - Authoritative data for all nodes within the zone.

   - Data that defines the top node of the zone (can be thought of
     as part of the authoritative data).

   - Data that describes delegated subzones, i.e., cuts around the
     bottom of the zone.

   - Data that allows access to name servers for subzones
     (sometimes called "glue" data).

All of this data is expressed in the form of RRs, so a zone can be
completely described in terms of a set of RRs.  Whole zones can be
transferred between name servers by transferring the RRs, either carried
in a series of messages or by FTPing a master file which is a textual
representation.

The authoritative data for a zone is simply all of the RRs attached to
all of the nodes from the top node of the zone down to leaf nodes or
nodes above cuts around the bottom edge of the zone.

Though logically part of the authoritative data, the RRs that describe
the top node of the zone are especially important to the zone's
management.  These RRs are of two types: name server RRs that list, one
per RR, all of the servers for the zone, and a single SOA RR that
describes zone management parameters.

The RRs that describe cuts around the bottom of the zone are NS RRs that
name the servers for the subzones.  Since the cuts are between nodes,
these RRs are NOT part of the authoritative data of the zone, and should
be exactly the same as the corresponding RRs in the top node of the
subzone.  Since name servers are always associated with zone boundaries,
NS RRs are only found at nodes which are the top node of some zone.  In
the data that makes up a zone, NS RRs are found at the top node of the



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zone (and are authoritative) and at cuts around the bottom of the zone
(where they are not authoritative), but never in between.

One of the goals of the zone structure is that any zone have all the
data required to set up communications with the name servers for any
subzones.  That is, parent zones have all the information needed to
access servers for their children zones.  The NS RRs that name the
servers for subzones are often not enough for this task since they name
the servers, but do not give their addresses.  In particular, if the
name of the name server is itself in the subzone, we could be faced with
the situation where the NS RRs tell us that in order to learn a name
server's address, we should contact the server using the address we wish
to learn.  To fix this problem, a zone contains "glue" RRs which are not
part of the authoritative data, and are address RRs for the servers.
These RRs are only necessary if the name server's name is "below" the
cut, and are only used as part of a referral response.

4.2.2. Administrative considerations

When some organization wants to control its own domain, the first step
is to identify the proper parent zone, and get the parent zone's owners
to agree to the delegation of control.  While there are no particular
technical constraints dealing with where in the tree this can be done,
there are some administrative groupings discussed in [<A href="../../../../rfc.net/rfc1032.html">RFC-1032</A>] which
deal with top level organization, and middle level zones are free to
create their own rules.  For example, one university might choose to use
a single zone, while another might choose to organize by subzones
dedicated to individual departments or schools.  [<A href="../../../../rfc.net/rfc1033.html">RFC-1033</A>] catalogs
available DNS software an discusses administration procedures.

Once the proper name for the new subzone is selected, the new owners
should be required to demonstrate redundant name server support.  Note
that there is no requirement that the servers for a zone reside in a
host which has a name in that domain.  In many cases, a zone will be
more accessible to the internet at large if its servers are widely
distributed rather than being within the physical facilities controlled
by the same organization that manages the zone.  For example, in the
current DNS, one of the name servers for the United Kingdom, or UK
domain, is found in the US.  This allows US hosts to get UK data without
using limited transatlantic bandwidth.

As the last installation step, the delegation NS RRs and glue RRs
necessary to make the delegation effective should be added to the parent