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19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek<title>Chapter�1.�Introduction</title>
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19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek<tr><th colspan="3" align="center">Chapter�1.�Introduction</th></tr>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek<tr>
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19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek</td>
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19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek</table>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek<hr>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek</div>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek<div class="chapter">
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek<div class="titlepage"><div><div><h1 class="title">
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek<a name="Bv9ARM.ch01"></a>Chapter�1.�Introduction</h1></div></div></div>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek<div class="toc">
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek<p><b>Table of Contents</b></p>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek<dl class="toc">
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek<dt><span class="section"><a href="Bv9ARM.ch01.html#doc_scope">Scope of Document</a></span></dt>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek<dt><span class="section"><a href="Bv9ARM.ch01.html#organization">Organization of This Document</a></span></dt>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek<dt><span class="section"><a href="Bv9ARM.ch01.html#conventions">Conventions Used in This Document</a></span></dt>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek<dt><span class="section"><a href="Bv9ARM.ch01.html#dns_overview">The Domain Name System (<acronym class="acronym">DNS</acronym>)</a></span></dt>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek<dd><dl>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek<dt><span class="section"><a href="Bv9ARM.ch01.html#dns_fundamentals">DNS Fundamentals</a></span></dt>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek<dt><span class="section"><a href="Bv9ARM.ch01.html#domain_names">Domains and Domain Names</a></span></dt>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek<dt><span class="section"><a href="Bv9ARM.ch01.html#zones">Zones</a></span></dt>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek<dt><span class="section"><a href="Bv9ARM.ch01.html#auth_servers">Authoritative Name Servers</a></span></dt>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek<dt><span class="section"><a href="Bv9ARM.ch01.html#cache_servers">Caching Name Servers</a></span></dt>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek<dt><span class="section"><a href="Bv9ARM.ch01.html#multi_role">Name Servers in Multiple Roles</a></span></dt>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek</dl></dd>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek</dl>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek</div>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek <p>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek The Internet Domain Name System (<acronym class="acronym">DNS</acronym>)
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek consists of the syntax
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek to specify the names of entities in the Internet in a hierarchical
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek manner, the rules used for delegating authority over names, and the
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek system implementation that actually maps names to Internet
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek addresses. <acronym class="acronym">DNS</acronym> data is maintained in a
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek group of distributed
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek hierarchical databases.
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek </p>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek <div class="section">
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek<div class="titlepage"><div><div><h2 class="title" style="clear: both">
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek<a name="doc_scope"></a>Scope of Document</h2></div></div></div>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek <p>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek The Berkeley Internet Name Domain
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek (<acronym class="acronym">BIND</acronym>) implements a
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek domain name server for a number of operating systems. This
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek document provides basic information about the installation and
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek care of the Internet Systems Consortium (<acronym class="acronym">ISC</acronym>)
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek <acronym class="acronym">BIND</acronym> version 9 software package for
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek system administrators.
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek </p>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek <p>This version of the manual corresponds to BIND version 9.11.</p>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek </div>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek <div class="section">
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek<div class="titlepage"><div><div><h2 class="title" style="clear: both">
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek<a name="organization"></a>Organization of This Document</h2></div></div></div>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek <p>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek In this document, <span class="emphasis"><em>Chapter 1</em></span> introduces
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek the basic <acronym class="acronym">DNS</acronym> and <acronym class="acronym">BIND</acronym> concepts. <span class="emphasis"><em>Chapter 2</em></span>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek describes resource requirements for running <acronym class="acronym">BIND</acronym> in various
a7893c6b28772edbc7e1fea3c209caa54d465648Lennart Poettering environments. Information in <span class="emphasis"><em>Chapter 3</em></span> is
a7893c6b28772edbc7e1fea3c209caa54d465648Lennart Poettering <span class="emphasis"><em>task-oriented</em></span> in its presentation and is
a7893c6b28772edbc7e1fea3c209caa54d465648Lennart Poettering organized functionally, to aid in the process of installing the
a7893c6b28772edbc7e1fea3c209caa54d465648Lennart Poettering <acronym class="acronym">BIND</acronym> 9 software. The task-oriented
a7893c6b28772edbc7e1fea3c209caa54d465648Lennart Poettering section is followed by
a7893c6b28772edbc7e1fea3c209caa54d465648Lennart Poettering <span class="emphasis"><em>Chapter 4</em></span>, which contains more advanced
a7893c6b28772edbc7e1fea3c209caa54d465648Lennart Poettering concepts that the system administrator may need for implementing
a7893c6b28772edbc7e1fea3c209caa54d465648Lennart Poettering certain options. <span class="emphasis"><em>Chapter 5</em></span>
a7893c6b28772edbc7e1fea3c209caa54d465648Lennart Poettering describes the <acronym class="acronym">BIND</acronym> 9 lightweight
a7893c6b28772edbc7e1fea3c209caa54d465648Lennart Poettering resolver. The contents of <span class="emphasis"><em>Chapter 6</em></span> are
a7893c6b28772edbc7e1fea3c209caa54d465648Lennart Poettering organized as in a reference manual to aid in the ongoing
a7893c6b28772edbc7e1fea3c209caa54d465648Lennart Poettering maintenance of the software. <span class="emphasis"><em>Chapter 7</em></span> addresses
a7893c6b28772edbc7e1fea3c209caa54d465648Lennart Poettering security considerations, and
a7893c6b28772edbc7e1fea3c209caa54d465648Lennart Poettering <span class="emphasis"><em>Chapter 8</em></span> contains troubleshooting help. The
a7893c6b28772edbc7e1fea3c209caa54d465648Lennart Poettering main body of the document is followed by several
a7893c6b28772edbc7e1fea3c209caa54d465648Lennart Poettering <span class="emphasis"><em>appendices</em></span> which contain useful reference
a7893c6b28772edbc7e1fea3c209caa54d465648Lennart Poettering information, such as a <span class="emphasis"><em>bibliography</em></span> and
a7893c6b28772edbc7e1fea3c209caa54d465648Lennart Poettering historic information related to <acronym class="acronym">BIND</acronym>
a7893c6b28772edbc7e1fea3c209caa54d465648Lennart Poettering and the Domain Name
63ba209d8bc64137ff1585d5878328c93cb81b61Jan Engelhardt System.
a7893c6b28772edbc7e1fea3c209caa54d465648Lennart Poettering </p>
a7893c6b28772edbc7e1fea3c209caa54d465648Lennart Poettering </div>
a7893c6b28772edbc7e1fea3c209caa54d465648Lennart Poettering <div class="section">
a7893c6b28772edbc7e1fea3c209caa54d465648Lennart Poettering<div class="titlepage"><div><div><h2 class="title" style="clear: both">
a7893c6b28772edbc7e1fea3c209caa54d465648Lennart Poettering<a name="conventions"></a>Conventions Used in This Document</h2></div></div></div>
a7893c6b28772edbc7e1fea3c209caa54d465648Lennart Poettering
a7893c6b28772edbc7e1fea3c209caa54d465648Lennart Poettering <p>
a7893c6b28772edbc7e1fea3c209caa54d465648Lennart Poettering In this document, we use the following general typographic
a7893c6b28772edbc7e1fea3c209caa54d465648Lennart Poettering conventions:
a7893c6b28772edbc7e1fea3c209caa54d465648Lennart Poettering </p>
a7893c6b28772edbc7e1fea3c209caa54d465648Lennart Poettering
63ba209d8bc64137ff1585d5878328c93cb81b61Jan Engelhardt <div class="informaltable">
a7893c6b28772edbc7e1fea3c209caa54d465648Lennart Poettering <table border="1">
a7893c6b28772edbc7e1fea3c209caa54d465648Lennart Poettering<colgroup>
a7893c6b28772edbc7e1fea3c209caa54d465648Lennart Poettering<col width="3.000in" class="1">
a7893c6b28772edbc7e1fea3c209caa54d465648Lennart Poettering<col width="2.625in" class="2">
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek</colgroup>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek<tbody>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek<tr>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek<td>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek <p>
f7f74d8ec46532f13a1dc418d550eaf76b339fa3Lennart Poettering <span class="emphasis"><em>To describe:</em></span>
7b870f607bcb8f445d4d29a776d12d9de3bf1487Jan Engelhardt </p>
7b870f607bcb8f445d4d29a776d12d9de3bf1487Jan Engelhardt </td>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek<td>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek <p>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek <span class="emphasis"><em>We use the style:</em></span>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek </p>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek </td>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek</tr>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek<tr>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek<td>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek <p>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek a pathname, filename, URL, hostname,
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek mailing list name, or new term or concept
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek </p>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek </td>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek<td>
f7f74d8ec46532f13a1dc418d550eaf76b339fa3Lennart Poettering <p>
7b870f607bcb8f445d4d29a776d12d9de3bf1487Jan Engelhardt <code class="filename">Fixed width</code>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek </p>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek </td>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek</tr>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek<tr>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek<td>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek <p>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek literal user
3fde5f30bda2a70d97f3dc8fa918e42e1c07cc2cLennart Poettering input
3fde5f30bda2a70d97f3dc8fa918e42e1c07cc2cLennart Poettering </p>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek </td>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek<td>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek <p>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek <strong class="userinput"><code>Fixed Width Bold</code></strong>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek </p>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek </td>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek</tr>
f7f74d8ec46532f13a1dc418d550eaf76b339fa3Lennart Poettering<tr>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek<td>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek <p>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek program output
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek </p>
f7f74d8ec46532f13a1dc418d550eaf76b339fa3Lennart Poettering </td>
f7f74d8ec46532f13a1dc418d550eaf76b339fa3Lennart Poettering<td>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek <p>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek <code class="computeroutput">Fixed Width</code>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek </p>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek </td>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek</tr>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek</tbody>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek</table>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek </div>
fbce11397f4d19821a9dfe66ee3ebe11cad90057Jan Engelhardt
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek <p>
f7f74d8ec46532f13a1dc418d550eaf76b339fa3Lennart Poettering The following conventions are used in descriptions of the
f7f74d8ec46532f13a1dc418d550eaf76b339fa3Lennart Poettering <acronym class="acronym">BIND</acronym> configuration file:</p>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek<div class="informaltable">
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek <table border="1">
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek<colgroup>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek<col width="3.000in" class="1">
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek<col width="2.625in" class="2">
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek</colgroup>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek<tbody>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek<tr>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek<td>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek <p>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek <span class="emphasis"><em>To describe:</em></span>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek </p>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek </td>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek<td>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek <p>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek <span class="emphasis"><em>We use the style:</em></span>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek </p>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek </td>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek</tr>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek<tr>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek<td>
4f8f66cb4236783cd3cbee97fefc9aaa8469ac08Zbigniew Jędrzejewski-Szmek <p>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek keywords
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek </p>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek </td>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek<td>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek <p>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek <code class="literal">Fixed Width</code>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek </p>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek </td>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek</tr>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek<tr>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek<td>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek <p>
4f8f66cb4236783cd3cbee97fefc9aaa8469ac08Zbigniew Jędrzejewski-Szmek variables
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek </p>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek </td>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek<td>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek <p>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek <code class="varname">Fixed Width</code>
7b870f607bcb8f445d4d29a776d12d9de3bf1487Jan Engelhardt </p>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek </td>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek</tr>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek<tr>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek<td>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek <p>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek Optional input
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek </p>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek </td>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek<td>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek <p>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek [<span class="optional">Text is enclosed in square brackets</span>]
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek </p>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek </td>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek</tr>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek</tbody>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek</table>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek </div>
4f8f66cb4236783cd3cbee97fefc9aaa8469ac08Zbigniew Jędrzejewski-Szmek<p>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek </p>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek </div>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek <div class="section">
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek<div class="titlepage"><div><div><h2 class="title" style="clear: both">
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek<a name="dns_overview"></a>The Domain Name System (<acronym class="acronym">DNS</acronym>)</h2></div></div></div>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek <p>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek The purpose of this document is to explain the installation
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek and upkeep of the <acronym class="acronym">BIND</acronym> (Berkeley Internet
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek Name Domain) software package, and we
4f8f66cb4236783cd3cbee97fefc9aaa8469ac08Zbigniew Jędrzejewski-Szmek begin by reviewing the fundamentals of the Domain Name System
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek (<acronym class="acronym">DNS</acronym>) as they relate to <acronym class="acronym">BIND</acronym>.
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek </p>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek <div class="section">
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek<div class="titlepage"><div><div><h3 class="title">
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek<a name="dns_fundamentals"></a>DNS Fundamentals</h3></div></div></div>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek <p>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek The Domain Name System (DNS) is a hierarchical, distributed
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek database. It stores information for mapping Internet host names to
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek IP
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek addresses and vice versa, mail routing information, and other data
04d39279245834494baccfdb9349db8bf80abd13Lennart Poettering used by Internet applications.
04d39279245834494baccfdb9349db8bf80abd13Lennart Poettering </p>
4f8f66cb4236783cd3cbee97fefc9aaa8469ac08Zbigniew Jędrzejewski-Szmek
04d39279245834494baccfdb9349db8bf80abd13Lennart Poettering <p>
04d39279245834494baccfdb9349db8bf80abd13Lennart Poettering Clients look up information in the DNS by calling a
04d39279245834494baccfdb9349db8bf80abd13Lennart Poettering <span class="emphasis"><em>resolver</em></span> library, which sends queries to one or
04d39279245834494baccfdb9349db8bf80abd13Lennart Poettering more <span class="emphasis"><em>name servers</em></span> and interprets the responses.
63ba209d8bc64137ff1585d5878328c93cb81b61Jan Engelhardt The <acronym class="acronym">BIND</acronym> 9 software distribution
04d39279245834494baccfdb9349db8bf80abd13Lennart Poettering contains a name server, <span class="command"><strong>named</strong></span>, and a
04d39279245834494baccfdb9349db8bf80abd13Lennart Poettering resolver library, <span class="command"><strong>liblwres</strong></span>.
04d39279245834494baccfdb9349db8bf80abd13Lennart Poettering </p>
04d39279245834494baccfdb9349db8bf80abd13Lennart Poettering
04d39279245834494baccfdb9349db8bf80abd13Lennart Poettering </div>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek <div class="section">
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek<div class="titlepage"><div><div><h3 class="title">
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek<a name="domain_names"></a>Domains and Domain Names</h3></div></div></div>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek <p>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek 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
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek organizational or administrative boundaries. Each node of the tree,
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek called a <span class="emphasis"><em>domain</em></span>, is given a label. The domain
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek name of the
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek node is the concatenation of all the labels on the path from the
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek node to the <span class="emphasis"><em>root</em></span> node. This is represented
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek in written form as a string of labels listed from right to left and
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek separated by dots. A label need only be unique within its parent
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek domain.
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek </p>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek <p>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek For example, a domain name for a host at the
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek company <span class="emphasis"><em>Example, Inc.</em></span> could be
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek <code class="literal">ourhost.example.com</code>,
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek where <code class="literal">com</code> is the
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek top level domain to which
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek <code class="literal">ourhost.example.com</code> belongs,
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek <code class="literal">example</code> is
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek a subdomain of <code class="literal">com</code>, and
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek <code class="literal">ourhost</code> is the
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek name of the host.
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek </p>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek <p>
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek For administrative purposes, the name space is partitioned into
a7893c6b28772edbc7e1fea3c209caa54d465648Lennart Poettering areas called <span class="emphasis"><em>zones</em></span>, each starting at a node and
a7893c6b28772edbc7e1fea3c209caa54d465648Lennart Poettering extending down to the leaf nodes or to nodes where other zones
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek start.
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek 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
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek <span class="emphasis"><em>DNS protocol</em></span>.
19887cd06a3af2f045e763986eda19e208bd3f85Zbigniew Jędrzejewski-Szmek </p>
<p>
The data associated with each domain name is stored in the
form of <span class="emphasis"><em>resource records</em></span> (<acronym class="acronym">RR</acronym>s).
Some of the supported resource record types are described in
<a class="xref" 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 &#8220;Types of Resource Records and When to Use Them&#8221;</a>.
</p>
<p>
For more detailed information about the design of the DNS and
the DNS protocol, please refer to the standards documents listed in
<a class="xref" href="Bv9ARM.ch11.html#rfcs" title="Request for Comments (RFCs)">the section called &#8220;Request for Comments (RFCs)&#8221;</a>.
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="zones"></a>Zones</h3></div></div></div>
<p>
To properly operate a name server, it is important to understand
the difference between a <span class="emphasis"><em>zone</em></span>
and a <span class="emphasis"><em>domain</em></span>.
</p>
<p>
As stated previously, a zone is a point of delegation in
the <acronym class="acronym">DNS</acronym> tree. A zone consists of
those contiguous parts of the domain
tree for which a name server has complete information and over which
it has authority. It contains all domain names from a certain point
downward in the domain tree except those which are delegated to
other zones. A delegation point is marked by one or more
<span class="emphasis"><em>NS records</em></span> in the
parent zone, which should be matched by equivalent NS records at
the root of the delegated zone.
</p>
<p>
For instance, consider the <code class="literal">example.com</code>
domain which includes names
such as <code class="literal">host.aaa.example.com</code> and
<code class="literal">host.bbb.example.com</code> even though
the <code class="literal">example.com</code> zone includes
only delegations for the <code class="literal">aaa.example.com</code> and
<code class="literal">bbb.example.com</code> zones. A zone can
map
exactly to a single domain, but could also include only part of a
domain, the rest of which could be delegated to other
name servers. Every name in the <acronym class="acronym">DNS</acronym>
tree is a
<span class="emphasis"><em>domain</em></span>, even if it is
<span class="emphasis"><em>terminal</em></span>, that is, has no
<span class="emphasis"><em>subdomains</em></span>. Every subdomain is a domain and
every domain except the root is also a subdomain. The terminology is
not intuitive and we suggest that you read RFCs 1033, 1034 and 1035
to
gain a complete understanding of this difficult and subtle
topic.
</p>
<p>
Though <acronym class="acronym">BIND</acronym> is called a "domain name
server",
it deals primarily in terms of zones. The master and slave
declarations in the <code class="filename">named.conf</code> file
specify
zones, not domains. When you ask some other site if it is willing to
be a slave server for your <span class="emphasis"><em>domain</em></span>, you are
actually asking for slave service for some collection of zones.
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="auth_servers"></a>Authoritative Name Servers</h3></div></div></div>
<p>
Each zone is served by at least
one <span class="emphasis"><em>authoritative name server</em></span>,
which contains the complete data for the zone.
To make the DNS tolerant of server and network failures,
most zones have two or more authoritative servers, on
different networks.
</p>
<p>
Responses from authoritative servers have the "authoritative
answer" (AA) bit set in the response packets. This makes them
easy to identify when debugging DNS configurations using tools like
<span class="command"><strong>dig</strong></span> (<a class="xref" href="Bv9ARM.ch03.html#diagnostic_tools" title="Diagnostic Tools">the section called &#8220;Diagnostic Tools&#8221;</a>).
</p>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="primary_master"></a>The Primary Master</h4></div></div></div>
<p>
The authoritative server where the master copy of the zone
data is maintained is called the
<span class="emphasis"><em>primary master</em></span> server, or simply the
<span class="emphasis"><em>primary</em></span>. Typically it loads the zone
contents from some local file edited by humans or perhaps
generated mechanically from some other local file which is
edited by humans. This file is called the
<span class="emphasis"><em>zone file</em></span> or
<span class="emphasis"><em>master file</em></span>.
</p>
<p>
In some cases, however, the master file may not be edited
by humans at all, but may instead be the result of
<span class="emphasis"><em>dynamic update</em></span> operations.
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="slave_server"></a>Slave Servers</h4></div></div></div>
<p>
The other authoritative servers, the <span class="emphasis"><em>slave</em></span>
servers (also known as <span class="emphasis"><em>secondary</em></span> servers)
load the zone contents from another server using a replication
process known as a <span class="emphasis"><em>zone transfer</em></span>.
Typically the data are transferred directly from the primary
master, but it is also possible to transfer it from another
slave. In other words, a slave server may itself act as a
master to a subordinate slave server.
</p>
<p>
Periodically, the slave server must send a refresh query to
determine whether the zone contents have been updated. This
is done by sending a query for the zone's SOA record and
checking whether the SERIAL field has been updated; if so,
a new transfer request is initiated. The timing of these
refresh queries is controlled by the SOA REFRESH and RETRY
fields, but can be overrridden with the
<span class="command"><strong>max-refresh-time</strong></span>,
<span class="command"><strong>min-refresh-time</strong></span>,
<span class="command"><strong>max-retry-time</strong></span>, and
<span class="command"><strong>min-retry-time</strong></span> options.
</p>
<p>
If the zone data cannot be updated within the time specified
by the SOA EXPIRE option (up to a hard-coded maximum of
24 weeks) then the slave zone expires and will no longer
respond to queries.
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="stealth_server"></a>Stealth Servers</h4></div></div></div>
<p>
Usually all of the zone's authoritative servers are listed in
NS records in the parent zone. These NS records constitute
a <span class="emphasis"><em>delegation</em></span> of the zone from the parent.
The authoritative servers are also listed in the zone file itself,
at the <span class="emphasis"><em>top level</em></span> or <span class="emphasis"><em>apex</em></span>
of the zone. You can list servers in the zone's top-level NS
records that are not in the parent's NS delegation, but you cannot
list servers in the parent's delegation that are not present at
the zone's top level.
</p>
<p>
A <span class="emphasis"><em>stealth server</em></span> is a server that is
authoritative for a zone but is not listed in that zone's NS
records. Stealth servers can be used for keeping a local copy of
a
zone to speed up access to the zone's records or to make sure that
the
zone is available even if all the "official" servers for the zone
are
inaccessible.
</p>
<p>
A configuration where the primary master server itself is a
stealth server is often referred to as a "hidden primary"
configuration. One use for this configuration is when the primary
master
is behind a firewall and therefore unable to communicate directly
with the outside world.
</p>
</div>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="cache_servers"></a>Caching Name Servers</h3></div></div></div>
<p>
The resolver libraries provided by most operating systems are
<span class="emphasis"><em>stub resolvers</em></span>, meaning that they are not
capable of
performing the full DNS resolution process by themselves by talking
directly to the authoritative servers. Instead, they rely on a
local
name server to perform the resolution on their behalf. Such a
server
is called a <span class="emphasis"><em>recursive</em></span> name server; it performs
<span class="emphasis"><em>recursive lookups</em></span> for local clients.
</p>
<p>
To improve performance, recursive servers cache the results of
the lookups they perform. Since the processes of recursion and
caching are intimately connected, the terms
<span class="emphasis"><em>recursive server</em></span> and
<span class="emphasis"><em>caching server</em></span> are often used synonymously.
</p>
<p>
The length of time for which a record may be retained in
the cache of a caching name server is controlled by the
Time To Live (TTL) field associated with each resource record.
</p>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="forwarder"></a>Forwarding</h4></div></div></div>
<p>
Even a caching name server does not necessarily perform
the complete recursive lookup itself. Instead, it can
<span class="emphasis"><em>forward</em></span> some or all of the queries
that it cannot satisfy from its cache to another caching name
server,
commonly referred to as a <span class="emphasis"><em>forwarder</em></span>.
</p>
<p>
There may be one or more forwarders,
and they are queried in turn until the list is exhausted or an
answer
is found. Forwarders are typically used when you do not
wish all the servers at a given site to interact directly with the
rest of
the Internet servers. A typical scenario would involve a number
of internal <acronym class="acronym">DNS</acronym> servers and an
Internet firewall. Servers unable
to pass packets through the firewall would forward to the server
that can do it, and that server would query the Internet <acronym class="acronym">DNS</acronym> servers
on the internal server's behalf.
</p>
</div>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="multi_role"></a>Name Servers in Multiple Roles</h3></div></div></div>
<p>
The <acronym class="acronym">BIND</acronym> name server can
simultaneously act as
a master for some zones, a slave for other zones, and as a caching
(recursive) server for a set of local clients.
</p>
<p>
However, since the functions of authoritative name service
and caching/recursive name service are logically separate, it is
often advantageous to run them on separate server machines.
A server that only provides authoritative name service
(an <span class="emphasis"><em>authoritative-only</em></span> server) can run with
recursion disabled, improving reliability and security.
A server that is not authoritative for any zones and only provides
recursive service to local
clients (a <span class="emphasis"><em>caching-only</em></span> server)
does not need to be reachable from the Internet at large and can
be placed inside a firewall.
</p>
</div>
</div>
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