66 lines
4.6 KiB
HTML
66 lines
4.6 KiB
HTML
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<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE html
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PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html lang="en-us" xml:lang="en-us">
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<meta name="DC.Type" content="concept" />
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<meta name="DC.Title" content="Understanding Domain Name System queries" />
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<meta name="abstract" content="This topic explains how Domain Name System (DNS) resolves queries on behalf of clients." />
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<meta name="description" content="This topic explains how Domain Name System (DNS) resolves queries on behalf of clients." />
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<meta name="copyright" content="(C) Copyright IBM Corporation 2004, 2006" />
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<link rel="stylesheet" type="text/css" href="./ic.css" />
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<title>Understanding Domain Name System queries</title>
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</head>
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<body id="rzakkconceptquery"><a name="rzakkconceptquery"><!-- --></a>
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<!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
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<h1 class="topictitle1">Understanding Domain Name System queries</h1>
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<div><p>This topic explains how Domain Name System (DNS) resolves queries
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on behalf of clients.</p>
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<p>Clients use DNS servers to find information for them. The request might
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come directly from the client, or from an application running on the client.
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The client sends a query message to the DNS server that contains a fully qualified
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domain name (FQDN), a query type, such as a particular resource record the
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client requires, and the class for the domain name, which is typically the
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Internet (IN) class. The following figure depicts the sample network from
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the Single DNS server with Internet access example.</p>
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<div class="fignone"><span class="figcap">Figure 1. Single DNS server with Internet access</span><br /><img src="rzakk501.gif" alt="Single DNS server with Internet access" /><br /></div>
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<p>Suppose that host <em>dataentry</em> queries the DNS server for graphics.mycompany.com.
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The DNS server uses its own zone data and responds with the IP address 10.1.1.253.</p>
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<p>Now suppose <em>dataentry</em> requests the IP address of www.jkl.com. This
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host is not in the DNS server's zone data. There are now two paths that can
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be followed, recursion or iteration. If a DNS server is set to use recursion,
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the server can query or contact other DNS servers on behalf of the requesting
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client to fully resolve the name, then send an answer back to the client.
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If the DNS server queries another DNS server, the requesting server will cache
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the answer, so it can use it the next time that it receives that query. A
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client can attempt to contact other DNS servers on its own behalf to resolve
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a name. In this process, called <em>iteration</em>, the client uses separate
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and additional queries based on referral answers from servers.</p>
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</div>
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<div>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="rzakkconceptparent.htm" title="This topic explains what Domain Name System (DNS) is and how it works. It also shows the different types of zones that can be defined on a DNS server.">Domain Name System concepts</a></div>
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</div>
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<div class="relref"><strong>Related reference</strong><br />
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<div><a href="rzakkconceptbasic.htm" title="This topic explains Domain Name System (DNS) zones and zone types.">Understanding zones</a></div>
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<div><a href="rzakkscenario2.htm" title="This example depicts a simple subnet with a Domain Name System (DNS) server connected directly to the Internet.">Example: Single Domain Name System server with Internet access</a></div>
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</div>
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</div>
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</body>
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</html>
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