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7487ff578435377bbeefffdbfb78ca09ed1292dfTimo Sirainen<tr><th colspan="3" align="center">Chapter�5.�The <acronym class="acronym">BIND</acronym> 9 Lightweight Resolver</th></tr>
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8d3278a82b964217d95c340ec6f82037cdc59d19Timo Sirainen<div class="titlepage"><div><div><h2 class="title">
8d3278a82b964217d95c340ec6f82037cdc59d19Timo Sirainen<a name="Bv9ARM.ch05"></a>Chapter�5.�The <acronym class="acronym">BIND</acronym> 9 Lightweight Resolver</h2></div></div></div>
578ef2538ccf42e2a48234c24a8b709397101d88Timo Sirainen<dt><span class="sect1"><a href="Bv9ARM.ch05.html#id2577500">The Lightweight Resolver Library</a></span></dt>
578ef2538ccf42e2a48234c24a8b709397101d88Timo Sirainen<dt><span class="sect1"><a href="Bv9ARM.ch05.html#lwresd">Running a Resolver Daemon</a></span></dt>
d176f84ce5ca2073f4dfbafb457b9c74f6bf0d76Timo Sirainen<div class="titlepage"><div><div><h2 class="title" style="clear: both">
d176f84ce5ca2073f4dfbafb457b9c74f6bf0d76Timo Sirainen<a name="id2577500"></a>The Lightweight Resolver Library</h2></div></div></div>
8d3278a82b964217d95c340ec6f82037cdc59d19Timo Sirainen Traditionally applications have been linked with a stub resolver
8d3278a82b964217d95c340ec6f82037cdc59d19Timo Sirainen library that sends recursive DNS queries to a local caching name
e0740628f6ca05f4bc79a9d8a90b650f4d38d4d0Timo Sirainen IPv6 once introduced new complexity into the resolution process,
e0740628f6ca05f4bc79a9d8a90b650f4d38d4d0Timo Sirainen such as following A6 chains and DNAME records, and simultaneous
d176f84ce5ca2073f4dfbafb457b9c74f6bf0d76Timo Sirainen lookup of IPv4 and IPv6 addresses. Though most of the complexity was
3f603ef00e35fca21605afa0ad8d76e94fee2b96Timo Sirainen then removed, these are hard or impossible
3f603ef00e35fca21605afa0ad8d76e94fee2b96Timo Sirainen to implement in a traditional stub resolver.
86791365b10f45982c88e70f2eb94fd6c3fea151Timo Sirainen <acronym class="acronym">BIND</acronym> 9 therefore can also provide resolution
86791365b10f45982c88e70f2eb94fd6c3fea151Timo Sirainen services to local clients
86791365b10f45982c88e70f2eb94fd6c3fea151Timo Sirainen using a combination of a lightweight resolver library and a resolver
86791365b10f45982c88e70f2eb94fd6c3fea151Timo Sirainen daemon process running on the local host. These communicate using
86791365b10f45982c88e70f2eb94fd6c3fea151Timo Sirainen a simple UDP-based protocol, the "lightweight resolver protocol"
6fdfa4d4cf14d1d7764d7faa8258f112e39c8dbeTimo Sirainen that is distinct from and simpler than the full DNS protocol.
6fdfa4d4cf14d1d7764d7faa8258f112e39c8dbeTimo Sirainen<div class="titlepage"><div><div><h2 class="title" style="clear: both">
3f603ef00e35fca21605afa0ad8d76e94fee2b96Timo Sirainen<a name="lwresd"></a>Running a Resolver Daemon</h2></div></div></div>
d176f84ce5ca2073f4dfbafb457b9c74f6bf0d76Timo Sirainen To use the lightweight resolver interface, the system must
d176f84ce5ca2073f4dfbafb457b9c74f6bf0d76Timo Sirainen run the resolver daemon <span><strong class="command">lwresd</strong></span> or a
d176f84ce5ca2073f4dfbafb457b9c74f6bf0d76Timo Sirainen name server configured with a <span><strong class="command">lwres</strong></span>
d176f84ce5ca2073f4dfbafb457b9c74f6bf0d76Timo Sirainen By default, applications using the lightweight resolver library will
d176f84ce5ca2073f4dfbafb457b9c74f6bf0d76Timo Sirainen UDP requests to the IPv4 loopback address (127.0.0.1) on port 921.
d176f84ce5ca2073f4dfbafb457b9c74f6bf0d76Timo Sirainen address can be overridden by <span><strong class="command">lwserver</strong></span>
d176f84ce5ca2073f4dfbafb457b9c74f6bf0d76Timo Sirainen <code class="filename">/etc/resolv.conf</code>.
8d3278a82b964217d95c340ec6f82037cdc59d19Timo Sirainen The daemon currently only looks in the DNS, but in the future
8d3278a82b964217d95c340ec6f82037cdc59d19Timo Sirainen it may use other sources such as <code class="filename">/etc/hosts</code>,
b2d562f9c7fd13f9a16e9b3bcee904630b80b1feTimo Sirainen The <span><strong class="command">lwresd</strong></span> daemon is essentially a
8d3278a82b964217d95c340ec6f82037cdc59d19Timo Sirainen caching-only name server that responds to requests using the
d176f84ce5ca2073f4dfbafb457b9c74f6bf0d76Timo Sirainen resolver protocol rather than the DNS protocol. Because it needs
d176f84ce5ca2073f4dfbafb457b9c74f6bf0d76Timo Sirainen to run on each host, it is designed to require no or minimal
8d3278a82b964217d95c340ec6f82037cdc59d19Timo Sirainen configuration.
8d3278a82b964217d95c340ec6f82037cdc59d19Timo Sirainen Unless configured otherwise, it uses the name servers listed on
275385a2ecc58e41dc7df3ce3cd943caaa58c4d1Timo Sirainen <span><strong class="command">nameserver</strong></span> lines in <code class="filename">/etc/resolv.conf</code>
275385a2ecc58e41dc7df3ce3cd943caaa58c4d1Timo Sirainen as forwarders, but is also capable of doing the resolution
275385a2ecc58e41dc7df3ce3cd943caaa58c4d1Timo Sirainen autonomously if
8d3278a82b964217d95c340ec6f82037cdc59d19Timo Sirainen none are specified.
d176f84ce5ca2073f4dfbafb457b9c74f6bf0d76Timo Sirainen The <span><strong class="command">lwresd</strong></span> daemon may also be
d176f84ce5ca2073f4dfbafb457b9c74f6bf0d76Timo Sirainen configured with a
d176f84ce5ca2073f4dfbafb457b9c74f6bf0d76Timo Sirainen <code class="filename">named.conf</code> style configuration file,
8d3278a82b964217d95c340ec6f82037cdc59d19Timo Sirainen <code class="filename">/etc/lwresd.conf</code> by default. A name
8d3278a82b964217d95c340ec6f82037cdc59d19Timo Sirainen server may also
8d3278a82b964217d95c340ec6f82037cdc59d19Timo Sirainen 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>.