Bv9ARM.ch01.html revision b05bdb520d83f7ecaad708fe305268c3420be01d
3b4098640dd85040270f39b9a5ee5e22de99d3d6Mark Andrews - Copyright (C) 2004-2006 Internet Systems Consortium, Inc. ("ISC")
75c0816e8295e180f4bc7f10db3d0d880383bc1cMark Andrews - Copyright (C) 2000-2003 Internet Software Consortium.
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein - Permission to use, copy, modify, and distribute this software for any
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein - purpose with or without fee is hereby granted, provided that the above
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein - copyright notice and this permission notice appear in all copies.
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein - THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein - REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein - AND FITNESS. IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT,
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein - INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein - LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein - OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein - PERFORMANCE OF THIS SOFTWARE.
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60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein<link rel="next" href="Bv9ARM.ch02.html" title="Chapter�2.�BIND Resource Requirements">
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60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein<tr><th colspan="3" align="center">Chapter�1.�Introduction</th></tr>
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein<a accesskey="p" href="Bv9ARM.html">Prev</a>�</td>
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60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein<div class="titlepage"><div><div><h2 class="title">
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein<a name="Bv9ARM.ch01"></a>Chapter�1.�Introduction</h2></div></div></div>
b15d6bddeb80c985f42986dba362c2aaf8803462Mark Andrews<dt><span class="sect1"><a href="Bv9ARM.ch01.html#id2544701">Scope of Document</a></span></dt>
b15d6bddeb80c985f42986dba362c2aaf8803462Mark Andrews<dt><span class="sect1"><a href="Bv9ARM.ch01.html#id2544132">Organization of This Document</a></span></dt>
b15d6bddeb80c985f42986dba362c2aaf8803462Mark Andrews<dt><span class="sect1"><a href="Bv9ARM.ch01.html#id2544545">Conventions Used in This Document</a></span></dt>
b15d6bddeb80c985f42986dba362c2aaf8803462Mark Andrews<dt><span class="sect1"><a href="Bv9ARM.ch01.html#id2545545">The Domain Name System (<span class="acronym">DNS</span>)</a></span></dt>
b15d6bddeb80c985f42986dba362c2aaf8803462Mark Andrews<dt><span class="sect2"><a href="Bv9ARM.ch01.html#id2545566">DNS Fundamentals</a></span></dt>
b15d6bddeb80c985f42986dba362c2aaf8803462Mark Andrews<dt><span class="sect2"><a href="Bv9ARM.ch01.html#id2545669">Domains and Domain Names</a></span></dt>
b15d6bddeb80c985f42986dba362c2aaf8803462Mark Andrews<dt><span class="sect2"><a href="Bv9ARM.ch01.html#id2548211">Zones</a></span></dt>
b15d6bddeb80c985f42986dba362c2aaf8803462Mark Andrews<dt><span class="sect2"><a href="Bv9ARM.ch01.html#id2548288">Authoritative Name Servers</a></span></dt>
b15d6bddeb80c985f42986dba362c2aaf8803462Mark Andrews<dt><span class="sect2"><a href="Bv9ARM.ch01.html#id2548392">Caching Name Servers</a></span></dt>
b15d6bddeb80c985f42986dba362c2aaf8803462Mark Andrews<dt><span class="sect2"><a href="Bv9ARM.ch01.html#id2548454">Name Servers in Multiple Roles</a></span></dt>
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein The Internet Domain Name System (<span class="acronym">DNS</span>)
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein consists of the syntax
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein to specify the names of entities in the Internet in a hierarchical
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein manner, the rules used for delegating authority over names, and the
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein system implementation that actually maps names to Internet
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein addresses. <span class="acronym">DNS</span> data is maintained in a
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein group of distributed
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein hierarchical databases.
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein<div class="titlepage"><div><div><h2 class="title" style="clear: both">
b15d6bddeb80c985f42986dba362c2aaf8803462Mark Andrews<a name="id2544701"></a>Scope of Document</h2></div></div></div>
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein The Berkeley Internet Name Domain
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein (<span class="acronym">BIND</span>) implements an
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein domain name server for a number of operating systems. This
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein document provides basic information about the installation and
5a4557e8de2951a2796676b5ec4b6a90caa5be14Mark Andrews care of the Internet Systems Consortium (<span class="acronym">ISC</span>)
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein <span class="acronym">BIND</span> version 9 software package for
5a4557e8de2951a2796676b5ec4b6a90caa5be14Mark Andrews system administrators.
5a4557e8de2951a2796676b5ec4b6a90caa5be14Mark Andrews This version of the manual corresponds to BIND version 9.4.
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein<div class="titlepage"><div><div><h2 class="title" style="clear: both">
b15d6bddeb80c985f42986dba362c2aaf8803462Mark Andrews<a name="id2544132"></a>Organization of This Document</h2></div></div></div>
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein In this document, <span class="emphasis"><em>Section 1</em></span> introduces
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein the basic <span class="acronym">DNS</span> and <span class="acronym">BIND</span> concepts. <span class="emphasis"><em>Section 2</em></span>
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein describes resource requirements for running <span class="acronym">BIND</span> in various
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein environments. Information in <span class="emphasis"><em>Section 3</em></span> is
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein <span class="emphasis"><em>task-oriented</em></span> in its presentation and is
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein organized functionally, to aid in the process of installing the
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein <span class="acronym">BIND</span> 9 software. The task-oriented
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein section is followed by
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein <span class="emphasis"><em>Section 4</em></span>, which contains more advanced
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein concepts that the system administrator may need for implementing
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein certain options. <span class="emphasis"><em>Section 5</em></span>
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein describes the <span class="acronym">BIND</span> 9 lightweight
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein resolver. The contents of <span class="emphasis"><em>Section 6</em></span> are
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein organized as in a reference manual to aid in the ongoing
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein maintenance of the software. <span class="emphasis"><em>Section 7</em></span> addresses
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein security considerations, and
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein <span class="emphasis"><em>Section 8</em></span> contains troubleshooting help. The
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein main body of the document is followed by several
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein <span class="emphasis"><em>Appendices</em></span> which contain useful reference
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein information, such as a <span class="emphasis"><em>Bibliography</em></span> and
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein historic information related to <span class="acronym">BIND</span>
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein and the Domain Name
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein<div class="titlepage"><div><div><h2 class="title" style="clear: both">
b15d6bddeb80c985f42986dba362c2aaf8803462Mark Andrews<a name="id2544545"></a>Conventions Used in This Document</h2></div></div></div>
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein In this document, we use the following general typographic
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein conventions:
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein <span class="emphasis"><em>To describe:</em></span>
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein <span class="emphasis"><em>We use the style:</em></span>
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein a pathname, filename, URL, hostname,
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein mailing list name, or new term or concept
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein literal user
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein <strong class="userinput"><code>Fixed Width Bold</code></strong>
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein program output
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein The following conventions are used in descriptions of the
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein <span class="acronym">BIND</span> configuration file:</p>
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein <span class="emphasis"><em>To describe:</em></span>
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein <span class="emphasis"><em>We use the style:</em></span>
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein Optional input
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein [<span class="optional">Text is enclosed in square brackets</span>]
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein<div class="titlepage"><div><div><h2 class="title" style="clear: both">
b15d6bddeb80c985f42986dba362c2aaf8803462Mark Andrews<a name="id2545545"></a>The Domain Name System (<span class="acronym">DNS</span>)</h2></div></div></div>
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein The purpose of this document is to explain the installation
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein and upkeep of the <span class="acronym">BIND</span> software
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein package, and we
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein begin by reviewing the fundamentals of the Domain Name System
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein (<span class="acronym">DNS</span>) as they relate to <span class="acronym">BIND</span>.
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein<div class="titlepage"><div><div><h3 class="title">
b15d6bddeb80c985f42986dba362c2aaf8803462Mark Andrews<a name="id2545566"></a>DNS Fundamentals</h3></div></div></div>
5a4557e8de2951a2796676b5ec4b6a90caa5be14Mark Andrews The Domain Name System (DNS) is a hierarchical, distributed
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein database. It stores information for mapping Internet host names to
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein addresses and vice versa, mail routing information, and other data
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein used by Internet applications.
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein Clients look up information in the DNS by calling a
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein <span class="emphasis"><em>resolver</em></span> library, which sends queries to one or
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein more <span class="emphasis"><em>name servers</em></span> and interprets the responses.
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein The <span class="acronym">BIND</span> 9 software distribution
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein name server, <span><strong class="command">named</strong></span>, and two resolver
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein libraries, <span><strong class="command">liblwres</strong></span> and <span><strong class="command">libbind</strong></span>.
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein<div class="titlepage"><div><div><h3 class="title">
b15d6bddeb80c985f42986dba362c2aaf8803462Mark Andrews<a name="id2545669"></a>Domains and Domain Names</h3></div></div></div>
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein The data stored in the DNS is identified by <span class="emphasis"><em>domain names</em></span> that are organized as a tree according to
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein organizational or administrative boundaries. Each node of the tree,
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein called a <span class="emphasis"><em>domain</em></span>, is given a label. The domain
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein node is the concatenation of all the labels on the path from the
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein node to the <span class="emphasis"><em>root</em></span> node. This is represented
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein in written form as a string of labels listed from right to left and
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein separated by dots. A label need only be unique within its parent
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein For example, a domain name for a host at the
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein company <span class="emphasis"><em>Example, Inc.</em></span> could be
5a4557e8de2951a2796676b5ec4b6a90caa5be14Mark Andrews <code class="literal">ourhost.example.com</code>,
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein top level domain to which
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein <code class="literal">ourhost.example.com</code> belongs,
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein a subdomain of <code class="literal">com</code>, and
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein name of the host.
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein For administrative purposes, the name space is partitioned into
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein areas called <span class="emphasis"><em>zones</em></span>, each starting at a node and
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein extending down to the leaf nodes or to nodes where other zones
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein The data for each zone is stored in a <span class="emphasis"><em>name server</em></span>, which answers queries about the zone using the
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein <span class="emphasis"><em>DNS protocol</em></span>.
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein The data associated with each domain name is stored in the
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein form of <span class="emphasis"><em>resource records</em></span> (<span class="acronym">RR</span>s).
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein Some of the supported resource record types are described in
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein <a href="Bv9ARM.ch06.html#types_of_resource_records_and_when_to_use_them" title="Types of Resource Records and When to Use Them">the section called “Types of Resource Records and When to Use Them”</a>.
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein For more detailed information about the design of the DNS and
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein the DNS protocol, please refer to the standards documents listed in
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein <a href="Bv9ARM.ch09.html#rfcs" title="Request for Comments (RFCs)">the section called “Request for Comments (RFCs)”</a>.
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein<div class="titlepage"><div><div><h3 class="title">
b15d6bddeb80c985f42986dba362c2aaf8803462Mark Andrews<a name="id2548211"></a>Zones</h3></div></div></div>
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein To properly operate a name server, it is important to understand
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein the difference between a <span class="emphasis"><em>zone</em></span>
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein and a <span class="emphasis"><em>domain</em></span>.
5a4557e8de2951a2796676b5ec4b6a90caa5be14Mark Andrews As stated previously, a zone is a point of delegation in
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein the <span class="acronym">DNS</span> tree. A zone consists of
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein those contiguous parts of the domain
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein tree for which a name server has complete information and over which
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein it has authority. It contains all domain names from a certain point
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein downward in the domain tree except those which are delegated to
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein other zones. A delegation point is marked by one or more
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein <span class="emphasis"><em>NS records</em></span> in the
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein parent zone, which should be matched by equivalent NS records at
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein the root of the delegated zone.
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein For instance, consider the <code class="literal">example.com</code>
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein domain which includes names
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein such as <code class="literal">host.aaa.example.com</code> and
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein <code class="literal">host.bbb.example.com</code> even though
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein the <code class="literal">example.com</code> zone includes
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein only delegations for the <code class="literal">aaa.example.com</code> and
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein <code class="literal">bbb.example.com</code> zones. A zone can
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein exactly to a single domain, but could also include only part of a
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein domain, the rest of which could be delegated to other
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein name servers. Every name in the <span class="acronym">DNS</span>
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein <span class="emphasis"><em>domain</em></span>, even if it is
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein <span class="emphasis"><em>terminal</em></span>, that is, has no
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein <span class="emphasis"><em>subdomains</em></span>. Every subdomain is a domain and
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein every domain except the root is also a subdomain. The terminology is
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein not intuitive and we suggest that you read RFCs 1033, 1034 and 1035
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein gain a complete understanding of this difficult and subtle
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein Though <span class="acronym">BIND</span> is called a "domain name
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein it deals primarily in terms of zones. The master and slave
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein declarations in the <code class="filename">named.conf</code> file
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein zones, not domains. When you ask some other site if it is willing to
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein be a slave server for your <span class="emphasis"><em>domain</em></span>, you are
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein actually asking for slave service for some collection of zones.
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein<div class="titlepage"><div><div><h3 class="title">
b15d6bddeb80c985f42986dba362c2aaf8803462Mark Andrews<a name="id2548288"></a>Authoritative Name Servers</h3></div></div></div>
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein Each zone is served by at least
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein one <span class="emphasis"><em>authoritative name server</em></span>,
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein which contains the complete data for the zone.
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein To make the DNS tolerant of server and network failures,
5a4557e8de2951a2796676b5ec4b6a90caa5be14Mark Andrews most zones have two or more authoritative servers, on
5a4557e8de2951a2796676b5ec4b6a90caa5be14Mark Andrews different networks.
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein Responses from authoritative servers have the "authoritative
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein answer" (AA) bit set in the response packets. This makes them
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein easy to identify when debugging DNS configurations using tools like
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein <span><strong class="command">dig</strong></span> (<a href="Bv9ARM.ch03.html#diagnostic_tools" title="Diagnostic Tools">the section called “Diagnostic Tools”</a>).
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein<div class="titlepage"><div><div><h4 class="title">
b15d6bddeb80c985f42986dba362c2aaf8803462Mark Andrews<a name="id2548311"></a>The Primary Master</h4></div></div></div>
5a4557e8de2951a2796676b5ec4b6a90caa5be14Mark Andrews The authoritative server where the master copy of the zone
5a4557e8de2951a2796676b5ec4b6a90caa5be14Mark Andrews data is maintained is called the
5a4557e8de2951a2796676b5ec4b6a90caa5be14Mark Andrews <span class="emphasis"><em>primary master</em></span> server, or simply the
5a4557e8de2951a2796676b5ec4b6a90caa5be14Mark Andrews <span class="emphasis"><em>primary</em></span>. Typically it loads the zone
5a4557e8de2951a2796676b5ec4b6a90caa5be14Mark Andrews contents from some local file edited by humans or perhaps
5a4557e8de2951a2796676b5ec4b6a90caa5be14Mark Andrews generated mechanically from some other local file which is
5a4557e8de2951a2796676b5ec4b6a90caa5be14Mark Andrews edited by humans. This file is called the
5a4557e8de2951a2796676b5ec4b6a90caa5be14Mark Andrews <span class="emphasis"><em>zone file</em></span> or
5a4557e8de2951a2796676b5ec4b6a90caa5be14Mark Andrews <span class="emphasis"><em>master file</em></span>.
5a4557e8de2951a2796676b5ec4b6a90caa5be14Mark Andrews In some cases, however, the master file may not be edited
5a4557e8de2951a2796676b5ec4b6a90caa5be14Mark Andrews by humans at all, but may instead be the result of
5a4557e8de2951a2796676b5ec4b6a90caa5be14Mark Andrews <span class="emphasis"><em>dynamic update</em></span> operations.
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein<div class="titlepage"><div><div><h4 class="title">
b15d6bddeb80c985f42986dba362c2aaf8803462Mark Andrews<a name="id2548341"></a>Slave Servers</h4></div></div></div>
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein The other authoritative servers, the <span class="emphasis"><em>slave</em></span>
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein servers (also known as <span class="emphasis"><em>secondary</em></span> servers)
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein the zone contents from another server using a replication process
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein known as a <span class="emphasis"><em>zone transfer</em></span>. Typically the data
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein transferred directly from the primary master, but it is also
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein to transfer it from another slave. In other words, a slave server
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein may itself act as a master to a subordinate slave server.
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein<div class="titlepage"><div><div><h4 class="title">
b15d6bddeb80c985f42986dba362c2aaf8803462Mark Andrews<a name="id2548362"></a>Stealth Servers</h4></div></div></div>
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein Usually all of the zone's authoritative servers are listed in
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein NS records in the parent zone. These NS records constitute
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein a <span class="emphasis"><em>delegation</em></span> of the zone from the parent.
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein The authoritative servers are also listed in the zone file itself,
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein at the <span class="emphasis"><em>top level</em></span> or <span class="emphasis"><em>apex</em></span>
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein of the zone. You can list servers in the zone's top-level NS
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein records that are not in the parent's NS delegation, but you cannot
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein list servers in the parent's delegation that are not present at
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein the zone's top level.
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein A <span class="emphasis"><em>stealth server</em></span> is a server that is
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein authoritative for a zone but is not listed in that zone's NS
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein records. Stealth servers can be used for keeping a local copy of
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein zone to speed up access to the zone's records or to make sure that
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein zone is available even if all the "official" servers for the zone
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein inaccessible.
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein A configuration where the primary master server itself is a
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein stealth server is often referred to as a "hidden primary"
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein configuration. One use for this configuration is when the primary
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein is behind a firewall and therefore unable to communicate directly
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein with the outside world.
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein<div class="titlepage"><div><div><h3 class="title">
b15d6bddeb80c985f42986dba362c2aaf8803462Mark Andrews<a name="id2548392"></a>Caching Name Servers</h3></div></div></div>
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein The resolver libraries provided by most operating systems are
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein <span class="emphasis"><em>stub resolvers</em></span>, meaning that they are not
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein performing the full DNS resolution process by themselves by talking
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein directly to the authoritative servers. Instead, they rely on a
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein name server to perform the resolution on their behalf. Such a
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein is called a <span class="emphasis"><em>recursive</em></span> name server; it performs
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein <span class="emphasis"><em>recursive lookups</em></span> for local clients.
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein To improve performance, recursive servers cache the results of
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein the lookups they perform. Since the processes of recursion and
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein caching are intimately connected, the terms
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein <span class="emphasis"><em>recursive server</em></span> and
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein <span class="emphasis"><em>caching server</em></span> are often used synonymously.
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein The length of time for which a record may be retained in
b05bdb520d83f7ecaad708fe305268c3420be01dMark Andrews the cache of a caching name server is controlled by the
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein Time To Live (TTL) field associated with each resource record.
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein<div class="titlepage"><div><div><h4 class="title">
b15d6bddeb80c985f42986dba362c2aaf8803462Mark Andrews<a name="id2548427"></a>Forwarding</h4></div></div></div>
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein Even a caching name server does not necessarily perform
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein the complete recursive lookup itself. Instead, it can
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein <span class="emphasis"><em>forward</em></span> some or all of the queries
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein that it cannot satisfy from its cache to another caching name
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein commonly referred to as a <span class="emphasis"><em>forwarder</em></span>.
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein There may be one or more forwarders,
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein and they are queried in turn until the list is exhausted or an
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein is found. Forwarders are typically used when you do not
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein wish all the servers at a given site to interact directly with the
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein the Internet servers. A typical scenario would involve a number
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein of internal <span class="acronym">DNS</span> servers and an
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein Internet firewall. Servers unable
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein to pass packets through the firewall would forward to the server
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein that can do it, and that server would query the Internet <span class="acronym">DNS</span> servers
5a4557e8de2951a2796676b5ec4b6a90caa5be14Mark Andrews on the internal server's behalf.
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein<div class="titlepage"><div><div><h3 class="title">
b15d6bddeb80c985f42986dba362c2aaf8803462Mark Andrews<a name="id2548454"></a>Name Servers in Multiple Roles</h3></div></div></div>
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein The <span class="acronym">BIND</span> name server can
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein simultaneously act as
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein a master for some zones, a slave for other zones, and as a caching
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein (recursive) server for a set of local clients.
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein However, since the functions of authoritative name service
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein and caching/recursive name service are logically separate, it is
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein often advantageous to run them on separate server machines.
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein A server that only provides authoritative name service
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein (an <span class="emphasis"><em>authoritative-only</em></span> server) can run with
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein recursion disabled, improving reliability and security.
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein A server that is not authoritative for any zones and only provides
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein recursive service to local
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein clients (a <span class="emphasis"><em>caching-only</em></span> server)
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein does not need to be reachable from the Internet at large and can
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein be placed inside a firewall.
60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein<a accesskey="p" href="Bv9ARM.html">Prev</a>�</td>
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60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein<td width="40%" align="left" valign="top">BIND 9 Administrator Reference Manual�</td>
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60e5e10f8d2e2b0c41e8abad38cacd867caa6ab2Rob Austein<td width="40%" align="right" valign="top">�Chapter�2.�<span class="acronym">BIND</span> Resource Requirements</td>