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6aaa468f50af23f08685835d1984767b81a4446aDerek Gathright - Copyright (C) 2004, 2005 Internet Systems Consortium, Inc. ("ISC")
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6aaa468f50af23f08685835d1984767b81a4446aDerek Gathright<title>Chapter�5.�The BIND 9 Lightweight Resolver</title>
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6aaa468f50af23f08685835d1984767b81a4446aDerek Gathright<tr><th colspan="3" align="center">Chapter�5.�The <span class="acronym">BIND</span> 9 Lightweight Resolver</th></tr>
6aaa468f50af23f08685835d1984767b81a4446aDerek Gathright<a accesskey="p" href="Bv9ARM.ch04.html">Prev</a>�</td>
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b28e90463180540ce576a7941dcade8d95beee76Derek Gathright<div class="titlepage"><div><div><h2 class="title">
b28e90463180540ce576a7941dcade8d95beee76Derek Gathright<a name="Bv9ARM.ch05"></a>Chapter�5.�The <span class="acronym">BIND</span> 9 Lightweight Resolver</h2></div></div></div>
6aaa468f50af23f08685835d1984767b81a4446aDerek Gathright<dt><span class="sect1"><a href="Bv9ARM.ch05.html#id2541275">The Lightweight Resolver Library</a></span></dt>
6aaa468f50af23f08685835d1984767b81a4446aDerek Gathright<dt><span class="sect1"><a href="Bv9ARM.ch05.html#lwresd">Running a Resolver Daemon</a></span></dt>
6aaa468f50af23f08685835d1984767b81a4446aDerek Gathright<div class="titlepage"><div><div><h2 class="title" style="clear: both">
6aaa468f50af23f08685835d1984767b81a4446aDerek Gathright<a name="id2541275"></a>The Lightweight Resolver Library</h2></div></div></div>
db92b84e128cab8bd1aecfa3c38718a339eb501fDerek Gathright Traditionally applications have been linked with a stub resolver
db92b84e128cab8bd1aecfa3c38718a339eb501fDerek Gathright library that sends recursive DNS queries to a local caching name
6aaa468f50af23f08685835d1984767b81a4446aDerek Gathright IPv6 once introduced new complexity into the resolution process,
6aaa468f50af23f08685835d1984767b81a4446aDerek Gathright such as following A6 chains and DNAME records, and simultaneous
6aaa468f50af23f08685835d1984767b81a4446aDerek Gathright lookup of IPv4 and IPv6 addresses. Though most of the complexity was
6aaa468f50af23f08685835d1984767b81a4446aDerek Gathright then removed, these are hard or impossible
6aaa468f50af23f08685835d1984767b81a4446aDerek Gathright to implement in a traditional stub resolver.
6aaa468f50af23f08685835d1984767b81a4446aDerek Gathright Instead, <span class="acronym">BIND</span> 9 provides resolution
6aaa468f50af23f08685835d1984767b81a4446aDerek Gathright services to local clients
6aaa468f50af23f08685835d1984767b81a4446aDerek Gathright using a combination of a lightweight resolver library and a resolver
6aaa468f50af23f08685835d1984767b81a4446aDerek Gathright daemon process running on the local host. These communicate using
6aaa468f50af23f08685835d1984767b81a4446aDerek Gathright a simple UDP-based protocol, the "lightweight resolver protocol"
6aaa468f50af23f08685835d1984767b81a4446aDerek Gathright that is distinct from and simpler than the full DNS protocol.
6aaa468f50af23f08685835d1984767b81a4446aDerek Gathright<div class="titlepage"><div><div><h2 class="title" style="clear: both">
6aaa468f50af23f08685835d1984767b81a4446aDerek Gathright<a name="lwresd"></a>Running a Resolver Daemon</h2></div></div></div>
b28e90463180540ce576a7941dcade8d95beee76Derek Gathright To use the lightweight resolver interface, the system must
6aaa468f50af23f08685835d1984767b81a4446aDerek Gathright run the resolver daemon <span><strong class="command">lwresd</strong></span> or a
6aaa468f50af23f08685835d1984767b81a4446aDerek Gathright name server configured with a <span><strong class="command">lwres</strong></span>
6aaa468f50af23f08685835d1984767b81a4446aDerek Gathright By default, applications using the lightweight resolver library will
6aaa468f50af23f08685835d1984767b81a4446aDerek Gathright UDP requests to the IPv4 loopback address (127.0.0.1) on port 921.
6aaa468f50af23f08685835d1984767b81a4446aDerek Gathright address can be overridden by <span><strong class="command">lwserver</strong></span>
6aaa468f50af23f08685835d1984767b81a4446aDerek Gathright <code class="filename">/etc/resolv.conf</code>.
6aaa468f50af23f08685835d1984767b81a4446aDerek Gathright The daemon currently only looks in the DNS, but in the future
6aaa468f50af23f08685835d1984767b81a4446aDerek Gathright it may use other sources such as <code class="filename">/etc/hosts</code>,
6aaa468f50af23f08685835d1984767b81a4446aDerek Gathright The <span><strong class="command">lwresd</strong></span> daemon is essentially a
6aaa468f50af23f08685835d1984767b81a4446aDerek Gathright caching-only name server that responds to requests using the
6aaa468f50af23f08685835d1984767b81a4446aDerek Gathright resolver protocol rather than the DNS protocol. Because it needs
6aaa468f50af23f08685835d1984767b81a4446aDerek Gathright to run on each host, it is designed to require no or minimal
6aaa468f50af23f08685835d1984767b81a4446aDerek Gathright configuration.
6aaa468f50af23f08685835d1984767b81a4446aDerek Gathright Unless configured otherwise, it uses the name servers listed on
6aaa468f50af23f08685835d1984767b81a4446aDerek Gathright <span><strong class="command">nameserver</strong></span> lines in <code class="filename">/etc/resolv.conf</code>
6aaa468f50af23f08685835d1984767b81a4446aDerek Gathright as forwarders, but is also capable of doing the resolution
6aaa468f50af23f08685835d1984767b81a4446aDerek Gathright autonomously if
db92b84e128cab8bd1aecfa3c38718a339eb501fDerek Gathright none are specified.
6aaa468f50af23f08685835d1984767b81a4446aDerek Gathright The <span><strong class="command">lwresd</strong></span> daemon may also be
6aaa468f50af23f08685835d1984767b81a4446aDerek Gathright configured with a
6aaa468f50af23f08685835d1984767b81a4446aDerek Gathright <code class="filename">named.conf</code> style configuration file,
6aaa468f50af23f08685835d1984767b81a4446aDerek Gathright <code class="filename">/etc/lwresd.conf</code> by default. A name
6aaa468f50af23f08685835d1984767b81a4446aDerek Gathright server may also
6aaa468f50af23f08685835d1984767b81a4446aDerek Gathright be configured to act as a lightweight resolver daemon using the
6aaa468f50af23f08685835d1984767b81a4446aDerek Gathright <span><strong class="command">lwres</strong></span> statement in <code class="filename">named.conf</code>.
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6aaa468f50af23f08685835d1984767b81a4446aDerek Gathright<td width="40%" align="left" valign="top">Chapter�4.�Advanced DNS Features�</td>
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6aaa468f50af23f08685835d1984767b81a4446aDerek Gathright<td width="40%" align="right" valign="top">�Chapter�6.�<span class="acronym">BIND</span> 9 Configuration Reference</td>