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33d85edf47749fa345d7b636b9b4b9d0d0386f44Dav Glass<title>Chapter�5.�The BIND 9 Lightweight Resolver</title>
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33d85edf47749fa345d7b636b9b4b9d0d0386f44Dav Glass<tr><th colspan="3" align="center">Chapter�5.�The <span class="acronym">BIND</span> 9 Lightweight Resolver</th></tr>
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33d85edf47749fa345d7b636b9b4b9d0d0386f44Dav Glass<div class="titlepage"><div><div><h2 class="title">
33d85edf47749fa345d7b636b9b4b9d0d0386f44Dav Glass<a name="Bv9ARM.ch05"></a>Chapter�5.�The <span class="acronym">BIND</span> 9 Lightweight Resolver</h2></div></div></div>
33d85edf47749fa345d7b636b9b4b9d0d0386f44Dav Glass<dt><span class="sect1"><a href="Bv9ARM.ch05.html#id2542240">The Lightweight Resolver Library</a></span></dt>
33d85edf47749fa345d7b636b9b4b9d0d0386f44Dav Glass<dt><span class="sect1"><a href="Bv9ARM.ch05.html#lwresd">Running a Resolver Daemon</a></span></dt>
33d85edf47749fa345d7b636b9b4b9d0d0386f44Dav Glass<div class="titlepage"><div><div><h2 class="title" style="clear: both">
33d85edf47749fa345d7b636b9b4b9d0d0386f44Dav Glass<a name="id2542240"></a>The Lightweight Resolver Library</h2></div></div></div>
33d85edf47749fa345d7b636b9b4b9d0d0386f44Dav Glass Traditionally applications have been linked with a stub resolver
33d85edf47749fa345d7b636b9b4b9d0d0386f44Dav Glass library that sends recursive DNS queries to a local caching name
33d85edf47749fa345d7b636b9b4b9d0d0386f44Dav Glass IPv6 once introduced new complexity into the resolution process,
33d85edf47749fa345d7b636b9b4b9d0d0386f44Dav Glass such as following A6 chains and DNAME records, and simultaneous
33d85edf47749fa345d7b636b9b4b9d0d0386f44Dav Glass lookup of IPv4 and IPv6 addresses. Though most of the complexity was
33d85edf47749fa345d7b636b9b4b9d0d0386f44Dav Glass then removed, these are hard or impossible
33d85edf47749fa345d7b636b9b4b9d0d0386f44Dav Glass to implement in a traditional stub resolver.
33d85edf47749fa345d7b636b9b4b9d0d0386f44Dav Glass <span class="acronym">BIND</span> 9 therefore can also provide resolution
33d85edf47749fa345d7b636b9b4b9d0d0386f44Dav Glass services to local clients
33d85edf47749fa345d7b636b9b4b9d0d0386f44Dav Glass using a combination of a lightweight resolver library and a resolver
33d85edf47749fa345d7b636b9b4b9d0d0386f44Dav Glass daemon process running on the local host. These communicate using
33d85edf47749fa345d7b636b9b4b9d0d0386f44Dav Glass a simple UDP-based protocol, the "lightweight resolver protocol"
33d85edf47749fa345d7b636b9b4b9d0d0386f44Dav Glass that is distinct from and simpler than the full DNS protocol.
33d85edf47749fa345d7b636b9b4b9d0d0386f44Dav Glass<div class="titlepage"><div><div><h2 class="title" style="clear: both">
33d85edf47749fa345d7b636b9b4b9d0d0386f44Dav Glass<a name="lwresd"></a>Running a Resolver Daemon</h2></div></div></div>
33d85edf47749fa345d7b636b9b4b9d0d0386f44Dav Glass To use the lightweight resolver interface, the system must
33d85edf47749fa345d7b636b9b4b9d0d0386f44Dav Glass run the resolver daemon <span><strong class="command">lwresd</strong></span> or a
33d85edf47749fa345d7b636b9b4b9d0d0386f44Dav Glass name server configured with a <span><strong class="command">lwres</strong></span>
33d85edf47749fa345d7b636b9b4b9d0d0386f44Dav Glass By default, applications using the lightweight resolver library will
33d85edf47749fa345d7b636b9b4b9d0d0386f44Dav Glass UDP requests to the IPv4 loopback address (127.0.0.1) on port 921.
33d85edf47749fa345d7b636b9b4b9d0d0386f44Dav Glass address can be overridden by <span><strong class="command">lwserver</strong></span>
33d85edf47749fa345d7b636b9b4b9d0d0386f44Dav Glass The daemon currently only looks in the DNS, but in the future
33d85edf47749fa345d7b636b9b4b9d0d0386f44Dav Glass it may use other sources such as <code class="filename">/etc/hosts</code>,
33d85edf47749fa345d7b636b9b4b9d0d0386f44Dav Glass The <span><strong class="command">lwresd</strong></span> daemon is essentially a
33d85edf47749fa345d7b636b9b4b9d0d0386f44Dav Glass caching-only name server that responds to requests using the
33d85edf47749fa345d7b636b9b4b9d0d0386f44Dav Glass resolver protocol rather than the DNS protocol. Because it needs
33d85edf47749fa345d7b636b9b4b9d0d0386f44Dav Glass to run on each host, it is designed to require no or minimal
33d85edf47749fa345d7b636b9b4b9d0d0386f44Dav Glass configuration.
33d85edf47749fa345d7b636b9b4b9d0d0386f44Dav Glass Unless configured otherwise, it uses the name servers listed on
33d85edf47749fa345d7b636b9b4b9d0d0386f44Dav Glass <span><strong class="command">nameserver</strong></span> lines in <code class="filename">/etc/resolv.conf</code>
33d85edf47749fa345d7b636b9b4b9d0d0386f44Dav Glass as forwarders, but is also capable of doing the resolution
33d85edf47749fa345d7b636b9b4b9d0d0386f44Dav Glass autonomously if
33d85edf47749fa345d7b636b9b4b9d0d0386f44Dav Glass none are specified.
33d85edf47749fa345d7b636b9b4b9d0d0386f44Dav Glass The <span><strong class="command">lwresd</strong></span> daemon may also be
33d85edf47749fa345d7b636b9b4b9d0d0386f44Dav Glass configured with a
33d85edf47749fa345d7b636b9b4b9d0d0386f44Dav Glass <code class="filename">named.conf</code> style configuration file,
33d85edf47749fa345d7b636b9b4b9d0d0386f44Dav Glass <code class="filename">/etc/lwresd.conf</code> by default. A name
33d85edf47749fa345d7b636b9b4b9d0d0386f44Dav Glass server may also
33d85edf47749fa345d7b636b9b4b9d0d0386f44Dav Glass be configured to act as a lightweight resolver daemon using the
33d85edf47749fa345d7b636b9b4b9d0d0386f44Dav Glass <span><strong class="command">lwres</strong></span> statement in <code class="filename">named.conf</code>.
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33d85edf47749fa345d7b636b9b4b9d0d0386f44Dav Glass<td width="40%" align="left" valign="top">Chapter�4.�Advanced DNS Features�</td>
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33d85edf47749fa345d7b636b9b4b9d0d0386f44Dav Glass<td width="40%" align="right" valign="top">�Chapter�6.�<span class="acronym">BIND</span> 9 Configuration Reference</td>