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4506N/A<title>Chapter�5.�The BIND 9 Lightweight Resolver</title>
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<div class="chapter" title="Chapter�5.�The BIND 9 Lightweight Resolver">
<div class="titlepage"><div><div><h2 class="title">
<a name="Bv9ARM.ch05"></a>Chapter�5.�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="section"><a href="Bv9ARM.ch05.html#idp72445136">The Lightweight Resolver Library</a></span></dt>
<dt><span class="section"><a href="Bv9ARM.ch05.html#lwresd">Running a Resolver Daemon</a></span></dt>
</dl>
</div>
<div class="section" title="The Lightweight Resolver Library">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="idp72445136"></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="section" title="Running a Resolver Daemon">
<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 class="command"><strong>lwresd</strong></span> or a
local
name server configured with a <span class="command"><strong>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 class="command"><strong>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 class="command"><strong>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 class="command"><strong>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 class="command"><strong>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 class="command"><strong>lwres</strong></span> statement in <code class="filename">named.conf</code>.
</p>
<p>
The number of client queries that the <span class="command"><strong>lwresd</strong></span>
daemon is able to serve can be set using the
<code class="option">lwres-tasks</code> and <code class="option">lwres-clients</code>
statements in the configuration.
</p>
</div>
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