external/bsd/bind/dist/doc/arm/Bv9ARM.ch05.html

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  21 <title>Chapter 5. The BIND 9 Lightweight Resolver</title>
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  31 <tr><th colspan="3" align="center">Chapter 5. The <acronym class="acronym">BIND</acronym> 9 Lightweight Resolver</th></tr>
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  42 <div class="chapter" lang="en">
  43 <div class="titlepage"><div><div><h2 class="title">
  44 <a name="Bv9ARM.ch05"></a>Chapter 5. The <acronym class="acronym">BIND</acronym> 9 Lightweight Resolver</h2></div></div></div>
  45 <div class="toc">
  46 <p><b>Table of Contents</b></p>
  47 <dl>
  48 <dt><span class="sect1"><a href="Bv9ARM.ch05.html#id2571844">The Lightweight Resolver Library</a></span></dt>
  49 <dt><span class="sect1"><a href="Bv9ARM.ch05.html#lwresd">Running a Resolver Daemon</a></span></dt>
  50 </dl>
  51 </div>
  52 <div class="sect1" lang="en">
  53 <div class="titlepage"><div><div><h2 class="title" style="clear: both">
  54 <a name="id2571844"></a>The Lightweight Resolver Library</h2></div></div></div>
  55 <p>
  56         Traditionally applications have been linked with a stub resolver
  57         library that sends recursive DNS queries to a local caching name
  58         server.
  59       </p>
  60 <p>
  61         IPv6 once introduced new complexity into the resolution process,
  62         such as following A6 chains and DNAME records, and simultaneous
  63         lookup of IPv4 and IPv6 addresses.  Though most of the complexity was
  64         then removed, these are hard or impossible
  65         to implement in a traditional stub resolver.
  66       </p>
  67 <p>
  68         <acronym class="acronym">BIND</acronym> 9 therefore can also provide resolution
  69         services to local clients
  70         using a combination of a lightweight resolver library and a resolver
  71         daemon process running on the local host.  These communicate using
  72         a simple UDP-based protocol, the "lightweight resolver protocol"
  73         that is distinct from and simpler than the full DNS protocol.
  74       </p>
  75 </div>
  76 <div class="sect1" lang="en">
  77 <div class="titlepage"><div><div><h2 class="title" style="clear: both">
  78 <a name="lwresd"></a>Running a Resolver Daemon</h2></div></div></div>
  79 <p>
  80         To use the lightweight resolver interface, the system must
  81         run the resolver daemon <span><strong class="command">lwresd</strong></span> or a
  82         local
  83         name server configured with a <span><strong class="command">lwres</strong></span>
  84         statement.
  85       </p>
  86 <p>
  87         By default, applications using the lightweight resolver library will
  88         make
  89         UDP requests to the IPv4 loopback address (127.0.0.1) on port 921.
  90         The
  91         address can be overridden by <span><strong class="command">lwserver</strong></span>
  92         lines in
  93         <code class="filename">/etc/resolv.conf</code>.
  94       </p>
  95 <p>
  96         The daemon currently only looks in the DNS, but in the future
  97         it may use other sources such as <code class="filename">/etc/hosts</code>,
  98         NIS, etc.
  99       </p>
 100 <p>
 101         The <span><strong class="command">lwresd</strong></span> daemon is essentially a
 102         caching-only name server that responds to requests using the
 103         lightweight
 104         resolver protocol rather than the DNS protocol.  Because it needs
 105         to run on each host, it is designed to require no or minimal
 106         configuration.
 107         Unless configured otherwise, it uses the name servers listed on
 108         <span><strong class="command">nameserver</strong></span> lines in <code class="filename">/etc/resolv.conf</code>
 109         as forwarders, but is also capable of doing the resolution
 110         autonomously if
 111         none are specified.
 112       </p>
 113 <p>
 114         The <span><strong class="command">lwresd</strong></span> daemon may also be
 115         configured with a
 116         <code class="filename">named.conf</code> style configuration file,
 117         in
 118         <code class="filename">/etc/lwresd.conf</code> by default.  A name
 119         server may also
 120         be configured to act as a lightweight resolver daemon using the
 121         <span><strong class="command">lwres</strong></span> statement in <code class="filename">named.conf</code>.
 122       </p>
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