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87d2c1ff6a7375f03476767e6f59454bcc5cd04bLennart Poettering<title>Chapter�5.�The BIND 9 Lightweight Resolver</title>
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0d43c6944bbca30d5692d4b02885f007a0c630c8Lennart Poettering<tr><th colspan="3" align="center">Chapter�5.�The <acronym class="acronym">BIND</acronym> 9 Lightweight Resolver</th></tr>
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e51240886f54e0128b1711c7dd0454b23e3f7d5eLennart Poettering<div class="titlepage"><div><div><h2 class="title">
0d43c6944bbca30d5692d4b02885f007a0c630c8Lennart Poettering<a name="Bv9ARM.ch05"></a>Chapter�5.�The <acronym class="acronym">BIND</acronym> 9 Lightweight Resolver</h2></div></div></div>
dca6219e04505e9fa10b32e71059ce2abfae1dadLennart Poettering<dt><span class="sect1"><a href="Bv9ARM.ch05.html#id2577560">The Lightweight Resolver Library</a></span></dt>
7560fffcd2531786b9c1ca657667a43e90331326Lennart Poettering<dt><span class="sect1"><a href="Bv9ARM.ch05.html#lwresd">Running a Resolver Daemon</a></span></dt>
4da416aa20b956571d74720bc91222881443e24bLennart Poettering<div class="titlepage"><div><div><h2 class="title" style="clear: both">
7560fffcd2531786b9c1ca657667a43e90331326Lennart Poettering<a name="id2577560"></a>The Lightweight Resolver Library</h2></div></div></div>
250d54b5bee6a46fe1c1626211e3a7e238eda628Lennart Poettering Traditionally applications have been linked with a stub resolver
df50185b43916926a72246ab3a80875eda7ad2a3Lennart Poettering library that sends recursive DNS queries to a local caching name
2100675e9fe0707fae8cee13fbe9316e94ef98f9Lennart Poettering IPv6 once introduced new complexity into the resolution process,
e91af489a25e8bb65016a63f533ae28a505119efLennart Poettering such as following A6 chains and DNAME records, and simultaneous
4367379907f40cbe7df6a64e51c36f34dd854197Lennart Poettering lookup of IPv4 and IPv6 addresses. Though most of the complexity was
9e8a535faa370bab283cb2c3c52b0a0d44e9d193Lennart Poettering then removed, these are hard or impossible
59cea26a349cfa8db906b520dac72563dd773ff2Lennart Poettering to implement in a traditional stub resolver.
941e990db1f2682abaa2966b1c48602901d0c599Lennart Poettering <acronym class="acronym">BIND</acronym> 9 therefore can also provide resolution
baed47c3c20512507e497058d388782400a072f6Lennart Poettering services to local clients
feb12d3ed2c7f9132c64773c7c41b9e3a608a814Lennart Poettering using a combination of a lightweight resolver library and a resolver
baed47c3c20512507e497058d388782400a072f6Lennart Poettering daemon process running on the local host. These communicate using
feb12d3ed2c7f9132c64773c7c41b9e3a608a814Lennart Poettering a simple UDP-based protocol, the "lightweight resolver protocol"
50f20cfdb0f127e415ab38c024d9ca7a3602f74bLennart Poettering that is distinct from and simpler than the full DNS protocol.
7560fffcd2531786b9c1ca657667a43e90331326Lennart Poettering<div class="titlepage"><div><div><h2 class="title" style="clear: both">
beec00856158b703f2125a3d936080346a8a8de1Lennart Poettering<a name="lwresd"></a>Running a Resolver Daemon</h2></div></div></div>
a1a03e3075316e2376176fc54c74e071adc9d71aLennart Poettering To use the lightweight resolver interface, the system must
7560fffcd2531786b9c1ca657667a43e90331326Lennart Poettering run the resolver daemon <span><strong class="command">lwresd</strong></span> or a
0d43c6944bbca30d5692d4b02885f007a0c630c8Lennart Poettering name server configured with a <span><strong class="command">lwres</strong></span>
baed47c3c20512507e497058d388782400a072f6Lennart Poettering By default, applications using the lightweight resolver library will
baed47c3c20512507e497058d388782400a072f6Lennart Poettering UDP requests to the IPv4 loopback address (127.0.0.1) on port 921.
8f14c8327b1c2b578bbf1235723a77931c3d0223Lennart Poettering address can be overridden by <span><strong class="command">lwserver</strong></span>
1705594f597ed12f38bee309b3fdb3f691e2021bLennart Poettering <code class="filename">/etc/resolv.conf</code>.
48383c251185c4596e9098878b28334c69e7bfd9Lennart Poettering The daemon currently only looks in the DNS, but in the future
baed47c3c20512507e497058d388782400a072f6Lennart Poettering it may use other sources such as <code class="filename">/etc/hosts</code>,
baed47c3c20512507e497058d388782400a072f6Lennart Poettering The <span><strong class="command">lwresd</strong></span> daemon is essentially a
7560fffcd2531786b9c1ca657667a43e90331326Lennart Poettering caching-only name server that responds to requests using the
baed47c3c20512507e497058d388782400a072f6Lennart Poettering resolver protocol rather than the DNS protocol. Because it needs
a1a03e3075316e2376176fc54c74e071adc9d71aLennart Poettering to run on each host, it is designed to require no or minimal
feb12d3ed2c7f9132c64773c7c41b9e3a608a814Lennart Poettering configuration.
baed47c3c20512507e497058d388782400a072f6Lennart Poettering Unless configured otherwise, it uses the name servers listed on
baed47c3c20512507e497058d388782400a072f6Lennart Poettering <span><strong class="command">nameserver</strong></span> lines in <code class="filename">/etc/resolv.conf</code>
baed47c3c20512507e497058d388782400a072f6Lennart Poettering as forwarders, but is also capable of doing the resolution
feb12d3ed2c7f9132c64773c7c41b9e3a608a814Lennart Poettering autonomously if
feb12d3ed2c7f9132c64773c7c41b9e3a608a814Lennart Poettering none are specified.
0d43c6944bbca30d5692d4b02885f007a0c630c8Lennart Poettering The <span><strong class="command">lwresd</strong></span> daemon may also be
0d43c6944bbca30d5692d4b02885f007a0c630c8Lennart Poettering configured with a
0d43c6944bbca30d5692d4b02885f007a0c630c8Lennart Poettering <code class="filename">named.conf</code> style configuration file,
0d43c6944bbca30d5692d4b02885f007a0c630c8Lennart Poettering <code class="filename">/etc/lwresd.conf</code> by default. A name
0d43c6944bbca30d5692d4b02885f007a0c630c8Lennart Poettering server may also
0d43c6944bbca30d5692d4b02885f007a0c630c8Lennart Poettering be configured to act as a lightweight resolver daemon using the
e91af489a25e8bb65016a63f533ae28a505119efLennart Poettering <span><strong class="command">lwres</strong></span> statement in <code class="filename">named.conf</code>.
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baed47c3c20512507e497058d388782400a072f6Lennart Poettering<td width="40%" align="right" valign="top">�Chapter�6.�<acronym class="acronym">BIND</acronym> 9 Configuration Reference</td>