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<title>Chapter5.The BIND 9 Lightweight Resolver</title>
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<tr><th colspan="3" align="center">Chapter5.The <acronym class="acronym">BIND</acronym> 9 Lightweight Resolver</th></tr>
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<div class="titlepage"><div><div><h2 class="title">
<a name="Bv9ARM.ch05"></a>Chapter5.The <acronym class="acronym">BIND</acronym> 9 Lightweight Resolver</h2></div></div></div>
<div class="toc">
<p><b>Table of Contents</b></p>
<dl>
<dt><span class="sect1"><a href="Bv9ARM.ch05.html#id2571925">The Lightweight Resolver Library</a></span></dt>
<dt><span class="sect1"><a href="Bv9ARM.ch05.html#lwresd">Running a Resolver Daemon</a></span></dt>
</dl>
</div>
<div class="sect1" lang="en">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="id2571925"></a>The Lightweight Resolver Library</h2></div></div></div>
<p>
        Traditionally applications have been linked with a stub resolver
        library that sends recursive DNS queries to a local caching name
        server.
      </p>
<p>
        IPv6 once introduced new complexity into the resolution process,
        such as following A6 chains and DNAME records, and simultaneous
        lookup of IPv4 and IPv6 addresses.  Though most of the complexity was
        then removed, these are hard or impossible
        to implement in a traditional stub resolver.
      </p>
<p>
        <acronym class="acronym">BIND</acronym> 9 therefore can also provide resolution
        services to local clients
        using a combination of a lightweight resolver library and a resolver
        daemon process running on the local host.  These communicate using
        a simple UDP-based protocol, the "lightweight resolver protocol"
        that is distinct from and simpler than the full DNS protocol.
      </p>
</div>
<div class="sect1" lang="en">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="lwresd"></a>Running a Resolver Daemon</h2></div></div></div>
<p>
        To use the lightweight resolver interface, the system must
        run the resolver daemon <span><strong class="command">lwresd</strong></span> or a
        local
        name server configured with a <span><strong class="command">lwres</strong></span>
        statement.
      </p>
<p>
        By default, applications using the lightweight resolver library will
        make
        UDP requests to the IPv4 loopback address (127.0.0.1) on port 921.
        The
        address can be overridden by <span><strong class="command">lwserver</strong></span>
        lines in
        <code class="filename">/etc/resolv.conf</code>.
      </p>
<p>
        The daemon currently only looks in the DNS, but in the future
        it may use other sources such as <code class="filename">/etc/hosts</code>,
        NIS, etc.
      </p>
<p>
        The <span><strong class="command">lwresd</strong></span> daemon is essentially a
        caching-only name server that responds to requests using the
        lightweight
        resolver protocol rather than the DNS protocol.  Because it needs
        to run on each host, it is designed to require no or minimal
        configuration.
        Unless configured otherwise, it uses the name servers listed on
        <span><strong class="command">nameserver</strong></span> lines in <code class="filename">/etc/resolv.conf</code>
        as forwarders, but is also capable of doing the resolution
        autonomously if
        none are specified.
      </p>
<p>
        The <span><strong class="command">lwresd</strong></span> daemon may also be
        configured with a
        <code class="filename">named.conf</code> style configuration file,
        in
        <code class="filename">/etc/lwresd.conf</code> by default.  A name
        server may also
        be configured to act as a lightweight resolver daemon using the
        <span><strong class="command">lwres</strong></span> statement in <code class="filename">named.conf</code>.
      </p>
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<td width="40%" align="left" valign="top">Chapter4.Advanced DNS Features</td>
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