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1ebb25608fa10737ea27abd4e0481707ccd45581Tinderbox User<title>Chapter�5.�The BIND 9 Lightweight Resolver</title>
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1ebb25608fa10737ea27abd4e0481707ccd45581Tinderbox User<tr><th colspan="3" align="center">Chapter�5.�The <acronym class="acronym">BIND</acronym> 9 Lightweight Resolver</th></tr>
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fd2597f75693a2279fdf588bd40dfe2407c42028Tinderbox User<div class="titlepage"><div><div><h2 class="title">
fd2597f75693a2279fdf588bd40dfe2407c42028Tinderbox User<a name="Bv9ARM.ch05"></a>Chapter�5.�The <acronym class="acronym">BIND</acronym> 9 Lightweight Resolver</h2></div></div></div>
1ebb25608fa10737ea27abd4e0481707ccd45581Tinderbox User<dt><span class="sect1"><a href="Bv9ARM.ch05.html#id2573017">The Lightweight Resolver Library</a></span></dt>
1ebb25608fa10737ea27abd4e0481707ccd45581Tinderbox User<dt><span class="sect1"><a href="Bv9ARM.ch05.html#lwresd">Running a Resolver Daemon</a></span></dt>
7e71f05d8643aca84914437c900cb716444507e4Tinderbox User<div class="titlepage"><div><div><h2 class="title" style="clear: both">
fd2597f75693a2279fdf588bd40dfe2407c42028Tinderbox User<a name="id2573017"></a>The Lightweight Resolver Library</h2></div></div></div>
fd2597f75693a2279fdf588bd40dfe2407c42028Tinderbox User Traditionally applications have been linked with a stub resolver
1ebb25608fa10737ea27abd4e0481707ccd45581Tinderbox User library that sends recursive DNS queries to a local caching name
1ebb25608fa10737ea27abd4e0481707ccd45581Tinderbox User IPv6 once introduced new complexity into the resolution process,
fd2597f75693a2279fdf588bd40dfe2407c42028Tinderbox User such as following A6 chains and DNAME records, and simultaneous
9d557856c2a19ec95ee73245f60a92f8675cf5baTinderbox User lookup of IPv4 and IPv6 addresses. Though most of the complexity was
1ebb25608fa10737ea27abd4e0481707ccd45581Tinderbox User then removed, these are hard or impossible
1ebb25608fa10737ea27abd4e0481707ccd45581Tinderbox User to implement in a traditional stub resolver.
fd2597f75693a2279fdf588bd40dfe2407c42028Tinderbox User <acronym class="acronym">BIND</acronym> 9 therefore can also provide resolution
1ebb25608fa10737ea27abd4e0481707ccd45581Tinderbox User services to local clients
fd2597f75693a2279fdf588bd40dfe2407c42028Tinderbox User using a combination of a lightweight resolver library and a resolver
14a656f94b1fd0ababd84a772228dfa52276ba15Evan Hunt daemon process running on the local host. These communicate using
1ebb25608fa10737ea27abd4e0481707ccd45581Tinderbox User a simple UDP-based protocol, the "lightweight resolver protocol"
fd2597f75693a2279fdf588bd40dfe2407c42028Tinderbox User that is distinct from and simpler than the full DNS protocol.
1ebb25608fa10737ea27abd4e0481707ccd45581Tinderbox User<div class="titlepage"><div><div><h2 class="title" style="clear: both">
fd2597f75693a2279fdf588bd40dfe2407c42028Tinderbox User<a name="lwresd"></a>Running a Resolver Daemon</h2></div></div></div>
fd2597f75693a2279fdf588bd40dfe2407c42028Tinderbox User To use the lightweight resolver interface, the system must
fd2597f75693a2279fdf588bd40dfe2407c42028Tinderbox User run the resolver daemon <span><strong class="command">lwresd</strong></span> or a
fd2597f75693a2279fdf588bd40dfe2407c42028Tinderbox User name server configured with a <span><strong class="command">lwres</strong></span>
fd2597f75693a2279fdf588bd40dfe2407c42028Tinderbox User By default, applications using the lightweight resolver library will
1ebb25608fa10737ea27abd4e0481707ccd45581Tinderbox User UDP requests to the IPv4 loopback address (127.0.0.1) on port 921.
1ebb25608fa10737ea27abd4e0481707ccd45581Tinderbox User address can be overridden by <span><strong class="command">lwserver</strong></span>
1ebb25608fa10737ea27abd4e0481707ccd45581Tinderbox User <code class="filename">/etc/resolv.conf</code>.
1ebb25608fa10737ea27abd4e0481707ccd45581Tinderbox User The daemon currently only looks in the DNS, but in the future
1ebb25608fa10737ea27abd4e0481707ccd45581Tinderbox User it may use other sources such as <code class="filename">/etc/hosts</code>,
1ebb25608fa10737ea27abd4e0481707ccd45581Tinderbox User The <span><strong class="command">lwresd</strong></span> daemon is essentially a
1ebb25608fa10737ea27abd4e0481707ccd45581Tinderbox User caching-only name server that responds to requests using the
1ebb25608fa10737ea27abd4e0481707ccd45581Tinderbox User resolver protocol rather than the DNS protocol. Because it needs
1ebb25608fa10737ea27abd4e0481707ccd45581Tinderbox User to run on each host, it is designed to require no or minimal
1ebb25608fa10737ea27abd4e0481707ccd45581Tinderbox User configuration.
c2258eedf2d9d0207b45b90014f8fde5413b41a3Tinderbox User Unless configured otherwise, it uses the name servers listed on
1ebb25608fa10737ea27abd4e0481707ccd45581Tinderbox User <span><strong class="command">nameserver</strong></span> lines in <code class="filename">/etc/resolv.conf</code>
1ebb25608fa10737ea27abd4e0481707ccd45581Tinderbox User as forwarders, but is also capable of doing the resolution
<span><strong class="command">lwres</strong></span> statement in <code class="filename">named.conf</code>.