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IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT, + - INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM + - LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE + - OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR + - PERFORMANCE OF THIS SOFTWARE. +--> +<!-- $Id: Bv9ARM.ch01.html,v 1.43 2008/09/25 06:24:40 tbox Exp $ --> +<html> +<head> +<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"> +<title>Chapter 1. Introduction</title> +<meta name="generator" content="DocBook XSL Stylesheets V1.71.1"> +<link rel="start" href="Bv9ARM.html" title="BIND 9 Administrator Reference Manual"> +<link rel="up" href="Bv9ARM.html" title="BIND 9 Administrator Reference Manual"> +<link rel="prev" href="Bv9ARM.html" title="BIND 9 Administrator Reference Manual"> +<link rel="next" href="Bv9ARM.ch02.html" title="Chapter 2. BIND Resource Requirements"> +</head> +<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> +<div class="navheader"> +<table width="100%" summary="Navigation header"> +<tr><th colspan="3" align="center">Chapter 1. Introduction</th></tr> +<tr> +<td width="20%" align="left"> +<a accesskey="p" href="Bv9ARM.html">Prev</a> </td> +<th width="60%" align="center"> </th> +<td width="20%" align="right"> <a accesskey="n" href="Bv9ARM.ch02.html">Next</a> +</td> +</tr> +</table> +<hr> +</div> +<div class="chapter" lang="en"> +<div class="titlepage"><div><div><h2 class="title"> +<a name="Bv9ARM.ch01"></a>Chapter 1. Introduction</h2></div></div></div> +<div class="toc"> +<p><b>Table of Contents</b></p> +<dl> +<dt><span class="sect1"><a href="Bv9ARM.ch01.html#id2563405">Scope of Document</a></span></dt> +<dt><span class="sect1"><a href="Bv9ARM.ch01.html#id2564385">Organization of This Document</a></span></dt> +<dt><span class="sect1"><a href="Bv9ARM.ch01.html#id2564524">Conventions Used in This Document</a></span></dt> +<dt><span class="sect1"><a href="Bv9ARM.ch01.html#id2564637">The Domain Name System (<acronym class="acronym">DNS</acronym>)</a></span></dt> +<dd><dl> +<dt><span class="sect2"><a href="Bv9ARM.ch01.html#id2564659">DNS Fundamentals</a></span></dt> +<dt><span class="sect2"><a href="Bv9ARM.ch01.html#id2564693">Domains and Domain Names</a></span></dt> +<dt><span class="sect2"><a href="Bv9ARM.ch01.html#id2564845">Zones</a></span></dt> +<dt><span class="sect2"><a href="Bv9ARM.ch01.html#id2567243">Authoritative Name Servers</a></span></dt> +<dt><span class="sect2"><a href="Bv9ARM.ch01.html#id2567416">Caching Name Servers</a></span></dt> +<dt><span class="sect2"><a href="Bv9ARM.ch01.html#id2567546">Name Servers in Multiple Roles</a></span></dt> +</dl></dd> +</dl> +</div> +<p> + The Internet Domain Name System (<acronym class="acronym">DNS</acronym>) + consists of the syntax + to specify the names of entities in the Internet in a hierarchical + manner, the rules used for delegating authority over names, and the + system implementation that actually maps names to Internet + addresses. <acronym class="acronym">DNS</acronym> data is maintained in a + group of distributed + hierarchical databases. + </p> +<div class="sect1" lang="en"> +<div class="titlepage"><div><div><h2 class="title" style="clear: both"> +<a name="id2563405"></a>Scope of Document</h2></div></div></div> +<p> + The Berkeley Internet Name Domain + (<acronym class="acronym">BIND</acronym>) implements a + domain name server for a number of operating systems. This + document provides basic information about the installation and + care of the Internet Systems Consortium (<acronym class="acronym">ISC</acronym>) + <acronym class="acronym">BIND</acronym> version 9 software package for + system administrators. + </p> +<p> + This version of the manual corresponds to BIND version 9.6. + </p> +</div> +<div class="sect1" lang="en"> +<div class="titlepage"><div><div><h2 class="title" style="clear: both"> +<a name="id2564385"></a>Organization of This Document</h2></div></div></div> +<p> + In this document, <span class="emphasis"><em>Section 1</em></span> introduces + the basic <acronym class="acronym">DNS</acronym> and <acronym class="acronym">BIND</acronym> concepts. <span class="emphasis"><em>Section 2</em></span> + describes resource requirements for running <acronym class="acronym">BIND</acronym> in various + environments. Information in <span class="emphasis"><em>Section 3</em></span> is + <span class="emphasis"><em>task-oriented</em></span> in its presentation and is + organized functionally, to aid in the process of installing the + <acronym class="acronym">BIND</acronym> 9 software. The task-oriented + section is followed by + <span class="emphasis"><em>Section 4</em></span>, which contains more advanced + concepts that the system administrator may need for implementing + certain options. <span class="emphasis"><em>Section 5</em></span> + describes the <acronym class="acronym">BIND</acronym> 9 lightweight + resolver. The contents of <span class="emphasis"><em>Section 6</em></span> are + organized as in a reference manual to aid in the ongoing + maintenance of the software. <span class="emphasis"><em>Section 7</em></span> addresses + security considerations, and + <span class="emphasis"><em>Section 8</em></span> contains troubleshooting help. The + main body of the document is followed by several + <span class="emphasis"><em>appendices</em></span> which contain useful reference + information, such as a <span class="emphasis"><em>bibliography</em></span> and + historic information related to <acronym class="acronym">BIND</acronym> + and the Domain Name + System. + </p> +</div> +<div class="sect1" lang="en"> +<div class="titlepage"><div><div><h2 class="title" style="clear: both"> +<a name="id2564524"></a>Conventions Used in This Document</h2></div></div></div> +<p> + In this document, we use the following general typographic + conventions: + </p> +<div class="informaltable"><table border="1"> +<colgroup> +<col> +<col> +</colgroup> +<tbody> +<tr> +<td> + <p> + <span class="emphasis"><em>To describe:</em></span> + </p> + </td> +<td> + <p> + <span class="emphasis"><em>We use the style:</em></span> + </p> + </td> +</tr> +<tr> +<td> + <p> + a pathname, filename, URL, hostname, + mailing list name, or new term or concept + </p> + </td> +<td> + <p> + <code class="filename">Fixed width</code> + </p> + </td> +</tr> +<tr> +<td> + <p> + literal user + input + </p> + </td> +<td> + <p> + <strong class="userinput"><code>Fixed Width Bold</code></strong> + </p> + </td> +</tr> +<tr> +<td> + <p> + program output + </p> + </td> +<td> + <p> + <code class="computeroutput">Fixed Width</code> + </p> + </td> +</tr> +</tbody> +</table></div> +<p> + The following conventions are used in descriptions of the + <acronym class="acronym">BIND</acronym> configuration file:</p> +<div class="informaltable"><table border="1"> +<colgroup> +<col> +<col> +</colgroup> +<tbody> +<tr> +<td> + <p> + <span class="emphasis"><em>To describe:</em></span> + </p> + </td> +<td> + <p> + <span class="emphasis"><em>We use the style:</em></span> + </p> + </td> +</tr> +<tr> +<td> + <p> + keywords + </p> + </td> +<td> + <p> + <code class="literal">Fixed Width</code> + </p> + </td> +</tr> +<tr> +<td> + <p> + variables + </p> + </td> +<td> + <p> + <code class="varname">Fixed Width</code> + </p> + </td> +</tr> +<tr> +<td> + <p> + Optional input + </p> + </td> +<td> + <p> + [<span class="optional">Text is enclosed in square brackets</span>] + </p> + </td> +</tr> +</tbody> +</table></div> +<p> + </p> +</div> +<div class="sect1" lang="en"> +<div class="titlepage"><div><div><h2 class="title" style="clear: both"> +<a name="id2564637"></a>The Domain Name System (<acronym class="acronym">DNS</acronym>)</h2></div></div></div> +<p> + The purpose of this document is to explain the installation + and upkeep of the <acronym class="acronym">BIND</acronym> (Berkeley Internet + Name Domain) software package, and we + begin by reviewing the fundamentals of the Domain Name System + (<acronym class="acronym">DNS</acronym>) as they relate to <acronym class="acronym">BIND</acronym>. + </p> +<div class="sect2" lang="en"> +<div class="titlepage"><div><div><h3 class="title"> +<a name="id2564659"></a>DNS Fundamentals</h3></div></div></div> +<p> + The Domain Name System (DNS) is a hierarchical, distributed + database. It stores information for mapping Internet host names to + IP + addresses and vice versa, mail routing information, and other data + used by Internet applications. + </p> +<p> + Clients look up information in the DNS by calling a + <span class="emphasis"><em>resolver</em></span> library, which sends queries to one or + more <span class="emphasis"><em>name servers</em></span> and interprets the responses. + The <acronym class="acronym">BIND</acronym> 9 software distribution + contains a + name server, <span><strong class="command">named</strong></span>, and a resolver + library, <span><strong class="command">liblwres</strong></span>. The older + <span><strong class="command">libbind</strong></span> resolver library is also available + from ISC as a separate download. + </p> +</div> +<div class="sect2" lang="en"> +<div class="titlepage"><div><div><h3 class="title"> +<a name="id2564693"></a>Domains and Domain Names</h3></div></div></div> +<p> + 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 + organizational or administrative boundaries. Each node of the tree, + called a <span class="emphasis"><em>domain</em></span>, is given a label. The domain + name of the + node is the concatenation of all the labels on the path from the + node to the <span class="emphasis"><em>root</em></span> node. This is represented + in written form as a string of labels listed from right to left and + separated by dots. A label need only be unique within its parent + domain. + </p> +<p> + For example, a domain name for a host at the + company <span class="emphasis"><em>Example, Inc.</em></span> could be + <code class="literal">ourhost.example.com</code>, + where <code class="literal">com</code> is the + top level domain to which + <code class="literal">ourhost.example.com</code> belongs, + <code class="literal">example</code> is + a subdomain of <code class="literal">com</code>, and + <code class="literal">ourhost</code> is the + name of the host. + </p> +<p> + For administrative purposes, the name space is partitioned into + areas called <span class="emphasis"><em>zones</em></span>, each starting at a node and + extending down to the leaf nodes or to nodes where other zones + start. + 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 + <span class="emphasis"><em>DNS protocol</em></span>. + </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 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>. + </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 href="Bv9ARM.ch09.html#rfcs" title="Request for Comments (RFCs)">the section called “Request for Comments (RFCs)”</a>. + </p> +</div> +<div class="sect2" lang="en"> +<div class="titlepage"><div><div><h3 class="title"> +<a name="id2564845"></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="sect2" lang="en"> +<div class="titlepage"><div><div><h3 class="title"> +<a name="id2567243"></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><strong class="command">dig</strong></span> (<a href="Bv9ARM.ch03.html#diagnostic_tools" title="Diagnostic Tools">the section called “Diagnostic Tools”</a>). + </p> +<div class="sect3" lang="en"> +<div class="titlepage"><div><div><h4 class="title"> +<a name="id2567267"></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="sect3" lang="en"> +<div class="titlepage"><div><div><h4 class="title"> +<a name="id2567297"></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> +</div> +<div class="sect3" lang="en"> +<div class="titlepage"><div><div><h4 class="title"> +<a name="id2567386"></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="sect2" lang="en"> +<div class="titlepage"><div><div><h3 class="title"> +<a name="id2567416"></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="sect3" lang="en"> +<div class="titlepage"><div><div><h4 class="title"> +<a name="id2567520"></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="sect2" lang="en"> +<div class="titlepage"><div><div><h3 class="title"> +<a name="id2567546"></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> +</div> +<div class="navfooter"> +<hr> +<table width="100%" summary="Navigation footer"> +<tr> +<td width="40%" align="left"> +<a accesskey="p" href="Bv9ARM.html">Prev</a> </td> +<td width="20%" align="center"> </td> +<td width="40%" align="right"> <a accesskey="n" href="Bv9ARM.ch02.html">Next</a> +</td> +</tr> +<tr> +<td width="40%" align="left" valign="top">BIND 9 Administrator Reference Manual </td> +<td width="20%" align="center"><a accesskey="h" href="Bv9ARM.html">Home</a></td> +<td width="40%" align="right" valign="top"> Chapter 2. <acronym class="acronym">BIND</acronym> Resource Requirements</td> +</tr> +</table> +</div> +</body> +</html> |