<HTML ><HEAD ><TITLE >The BIND 9 Lightweight Resolver</TITLE ><META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.73 "><LINK REL="HOME" TITLE="BIND 9 Administrator Reference Manual" HREF="Bv9ARM.html"><LINK REL="PREVIOUS" TITLE="Advanced Concepts" HREF="Bv9ARM.ch04.html"><LINK REL="NEXT" TITLE="BIND 9 Configuration Reference" HREF="Bv9ARM.ch06.html"></HEAD ><BODY CLASS="chapter" BGCOLOR="#FFFFFF" TEXT="#000000" LINK="#0000FF" VLINK="#840084" ALINK="#0000FF" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="3" ALIGN="center" >BIND 9 Administrator Reference Manual</TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="bottom" ><A HREF="Bv9ARM.ch04.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="80%" ALIGN="center" VALIGN="bottom" ></TD ><TD WIDTH="10%" ALIGN="right" VALIGN="bottom" ><A HREF="Bv9ARM.ch06.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="chapter" ><H1 ><A NAME="ch05" >Chapter 5. The <SPAN CLASS="acronym" >BIND</SPAN > 9 Lightweight Resolver</A ></H1 ><DIV CLASS="TOC" ><DL ><DT ><B >Table of Contents</B ></DT ><DT >5.1. <A HREF="Bv9ARM.ch05.html#AEN1063" >The Lightweight Resolver Library</A ></DT ><DT >5.2. <A HREF="Bv9ARM.ch05.html#lwresd" >Running a Resolver Daemon</A ></DT ></DL ></DIV ><DIV CLASS="sect1" ><H1 CLASS="sect1" ><A NAME="AEN1063" >5.1. The Lightweight Resolver Library</A ></H1 ><P >Traditionally applications have been linked with a stub resolver library that sends recursive DNS queries to a local caching name server.</P ><P >IPv6 introduces new complexity into the resolution process, such as following A6 chains and DNAME records, and simultaneous lookup of IPv4 and IPv6 addresses. These are hard or impossible to implement in a traditional stub resolver.</P ><P >Instead, <SPAN CLASS="acronym" >BIND</SPAN > 9 provides resolution services to local clients using a combination of a lightweight resolver library and a resolver daemon process running on the local host. These communicate using a simple UDP-based protocol, the "lightweight resolver protocol" that is distinct from and simpler than the full DNS protocol.</P ></DIV ><DIV CLASS="sect1" ><H1 CLASS="sect1" ><A NAME="lwresd" >5.2. Running a Resolver Daemon</A ></H1 ><P >To use the lightweight resolver interface, the system must run the resolver daemon <B CLASS="command" >lwresd</B >.</P ><P >By default, applications using the lightweight resolver library will make UDP requests to the IPv4 loopback address (127.0.0.1) on port 921. The address can be overridden by <B CLASS="command" >lwserver</B > lines in <TT CLASS="filename" >/etc/resolv.conf</TT >. The daemon will try to find the answer to the questions "what are the addresses for host <TT CLASS="literal" >foo.example.com</TT >?" and "what are the names for IPv4 address 10.1.2.3?"</P ><P >The daemon currently only looks in the DNS, but in the future it may use other sources such as <TT CLASS="filename" >/etc/hosts</TT >, NIS, etc.</P ><P >The <B CLASS="command" >lwresd</B > daemon is essentially a caching-only name server that answers requests using the lightweight resolver protocol rather than the DNS protocol. Because it needs to run on each host, it is designed to require no or minimal configuration. Unless configured otherwise, it uses the name servers listed on <B CLASS="command" >nameserver</B > lines in <TT CLASS="filename" >/etc/resolv.conf</TT > as forwarders, but is also capable of doing the resolution autonomously if none are specified.</P ><P >The <B CLASS="command" >lwresd</B > daemon may also be configured with a <TT CLASS="filename" >named.conf</TT > style configuration file, in <TT CLASS="filename" >/etc/lwresd.conf</TT > by default. A name server may also be configured to act as a lightweight resolver daemon using the <B CLASS="command" >lwres</B > statement in <TT CLASS="filename" >named.conf</TT >.</P ></DIV ></DIV ><DIV CLASS="NAVFOOTER" ><HR ALIGN="LEFT" WIDTH="100%"><TABLE SUMMARY="Footer navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><A HREF="Bv9ARM.ch04.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="Bv9ARM.html" ACCESSKEY="H" >Home</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><A HREF="Bv9ARM.ch06.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >Advanced Concepts</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" > </TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><SPAN CLASS="acronym" >BIND</SPAN > 9 Configuration Reference</TD ></TR ></TABLE ></DIV ></BODY ></HTML >