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<?xml version="1.0" encoding="iso-8859-1"?> <!-- -*-html-helper-*- -->
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<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>nss-mdns @PACKAGE_VERSION@</title>
<link rel="stylesheet" type="text/css" href="style.css" />
</head>
<body>
<h1><a name="top">nss-mdns @PACKAGE_VERSION@</a></h1>
<p><i>Copyright 2004-2006 Lennart Poettering <@PACKAGE_BUGREPORT@></i></p>
<ul class="toc">
<li><a href="#license">License</a></li>
<li><a href="#news">News</a></li>
<li><a href="#overview">Overview</a></li>
<li><a href="#status">Current Status</a></li>
<li><a href="#documentation">Documentation</a></li>
<li><a href="#requirements">Requirements</a></li>
<li><a href="#installation">Installation</a></li>
<li><a href="#acks">Acknowledgements</a></li>
<li><a href="#download">Download</a></li>
</ul>
<h2><a name="license">License</a></h2>
<p>This program is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public License as
published by the Free Software Foundation; either version 2 of the
License, or (at your option) any later version.</p>
<p>This program is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.</p>
<p>You should have received a copy of the GNU Lesser General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.</p>
<h2><a name="news">News</a></h2>
<div class="news-date">Sat Apr 29 2006: </div> <p class="news-text"><a
href="@PACKAGE_URL@nss-mdns-0.8.tar.gz">Version 0.8</a>
released. Changes include: Build time option to disable "legacy unicast" mDNS
requests, i.e. resolve exclusively with Avahi; build a special
<tt>_minimal</tt> flavour of the shared objects to minimize
unnecessary name lookup timeouts; fix IPv6 resolving when using
Avahi; <b>Please note that starting with nss-mdns 0.8 we encourage you to use a different <tt>/etc/nsswitch.conf</tt> configuration line. See below for more information!</b></p>
<div class="news-date">Sat Nov 19 2005: </div> <p class="news-text"><a
href="@PACKAGE_URL@nss-mdns-0.7.tar.gz">Version 0.7</a>
released. Changes include: Portability patch for ARM from Philipp
Zabel; make sure not to print any messages to STDERR; deal with OOM
situations properly; if multiple addresses are assigned to the same interface make sure to send a query packet only once; other cleanups</p>
<div class="news-date">Sun Aug 21 2005: </div> <p class="news-text"><a
href="@PACKAGE_URL@nss-mdns-0.6.tar.gz">Version 0.6</a>
released. Changes include: honour search list in
<tt>/etc/resolv.conf</tt>; try to contact <a
href="http://www.freedesktop.org/Software/Avahi">Avahi</a> for
resolving.</p>
<div class="news-date">Sat Jun 4 2005: </div> <p class="news-text"><a
href="@PACKAGE_URL@nss-mdns-0.5.tar.gz">Version 0.5</a>
released. Changes include: only lookup hostnames ending in
<tt>.local</tt>; add support for a configuration file
(<tt>/etc/mdns.allow</tt>) to allow lookups for other names.</p>
<div class="news-date">Sun May 15 2005: </div> <p class="news-text"><a
href="@PACKAGE_URL@nss-mdns-0.4.tar.gz">Version 0.4</a>
released. Changes include: small portability fix for big endian
architectures; send "legacy unicast" packets instead of normal mDNS
packets (this should reduce traffic and improve response time)</p>
<div class="news-date">Jan Sun 16 2005: </div> <p class="news-text"><a
href="@PACKAGE_URL@nss-mdns-0.3.tar.gz">Version 0.3</a>
released. Changes include: add Debianization; use <tt>ip6.arpa</tt> instead of <tt>ip6.int</tt> for reverse IPv6 lookups.</p>
<div class="news-date">Fri Dec 17 2004: </div> <p class="news-text"><a
href="@PACKAGE_URL@nss-mdns-0.2.tar.gz">Version 0.2</a>
released. Changes include: send mDNS queries on every interface that
supports multicasts, instead of only the one with the default route,
making <tt>nss-mdns</tt> more robust on multi-homed hosts; gcc 2.95
compatiblity.</p>
<div class="news-date">Mon Dec 6 2004: </div> <p class="news-text"><a
href="@PACKAGE_URL@nss-mdns-0.1.tar.gz">Version 0.1</a> released</p>
<h2><a name="overview">Overview</a></h2>
<p><tt>nss-mdns</tt> is a plugin for the GNU Name Service
Switch (NSS) functionality of the GNU C Library (<tt>glibc</tt>)
providing host name resolution via <a
href="http://www.multicastdns.org/">Multicast DNS</a> (aka
<i>Zeroconf</i>, aka <i>Apple Rendezvous</i>, aka <i>Apple Bonjour</i>), effectively allowing
name resolution by common Unix/Linux programs in the ad-hoc mDNS domain <tt>.local</tt>.</p>
<p><tt>nss-mdns</tt> provides client functionality only, which
means that you have to run a mDNS responder daemon seperately
from <tt>nss-mdns</tt> if you want to register the local host name via
mDNS. I recommend <a href="http://www.freedesktop.org/Software/Avahi">Avahi</a>.</p>
<p><tt>nss-mdns</tt> is very lightweight (24 KByte stripped binary
<tt>.so</tt> compiled with <tt>-DNDEBUG=1 -Os</tt> on i386, <tt>gcc</tt>
4.0), has no dependencies besides the <tt>glibc</tt> and requires only
minimal configuration.</p>
<p>Optionally <tt>nss-mdns</tt> can try to contact a running <a
href="http://www.freedesktop.org/Software/Avahi">avahi-daemon</a> to
make use of its superior record cacheing.</p>
<h2><a name="status">Current Status</a></h2>
<p>It works!</p>
<p>Although <tt>nss-mdns</tt> supports resolving IPv6 addresses it does
so via IPv4 multicasts only. (Unless, of course, it finds a running
Avahi daemon which supports IPv6 properly.)</p>
<h2><a name="documentation">Documentation</a></h2>
<p>After compiling and installing <tt>nss-mdns</tt> you'll find six
new NSS modules in <tt>/lib</tt>:</p>
<ul>
<li><tt>libnss_mdns.so.2</tt></li>
<li><tt>libnss_mdns4.so.2</tt></li>
<li><tt>libnss_mdns6.so.2</tt></li>
<li><tt>libnss_mdns_minimal.so.2</tt></li>
<li><tt>libnss_mdns4_minimal.so.2</tt></li>
<li><tt>libnss_mdns6_minimal.so.2</tt></li>
</ul>
<p><tt>libnss_mdns.so.2</tt>
resolves both IPv6 and IPv4 addresses, <tt>libnss_mdns4.so.2</tt> only
IPv4 addresses and <tt>libnss_mdns6.so.2</tt> only IPv6 addresses. Due
to the fact that most mDNS responders only register local IPv4
addresses via mDNS, most people will want to use
<tt>libnss_mdns4.so.2</tt> exclusively. Using
<tt>libnss_mdns.so.2</tt> or <tt>libnss_mdns6.so.2</tt> in such a
situation causes long timeouts when resolving hosts since most modern
Unix/Linux applications check for IPv6 addresses first, followed by a
lookup for IPv4.</p>
<p><tt>libnss_mdns{4,6,}_minimal.so</tt> (new in version 0.8) is mostly identical to the
versions without <tt>_minimal</tt>. However, they differ in one
way. The minimal versions will always deny to resolve host names that
don't end in <tt>.local</tt> or addresses that aren't in the range
<tt>169.254.x.x</tt> (the range used by <a
href="http://files.zeroconf.org/rfc3927.txt">IPV4LL/APIPA/RFC3927</a>.)
Combining the <tt>_minimal</tt> and the normal NSS modules allows us
to make mDNS authoritative for Zeroconf host names and addresses (and
thus creating no extra burden on DNS servers with always failing
requests) and use it as fallback for everything else.</p>
<p>To activate one of the NSS modules you have to edit
<tt>/etc/nsswitch.conf</tt> and add <tt>mdns4</tt> and
<tt>mdns4_minimal</tt> (resp. <tt>mdns</tt>, <tt>mdns6</tt>) to the
line starting with "<tt>hosts:</tt>". On Debian this looks like
this:</p>
<pre># /etc/nsswitch.conf
passwd: compat
group: compat
shadow: compat
hosts: files <b>mdns4_minimal [NOTFOUND=return]</b> dns <b>mdns4</b>
networks: files
protocols: db files
services: db files
ethers: db files
rpc: db files
netgroup: nis</pre>
<p>That's it. You should now be able to resolve hosts from the
<tt>.local</tt> domain with all your applications. For a quick check
use <tt>glibc</tt>'s <tt>getent</tt> tool:
<pre>$ getent hosts <i>foo</i>.local
192.168.50.4 foo.local</pre>
<p>Replace <i>foo</i> whith a host name that has been registered with
an mDNS responder. (Don't try to use the tools <tt>host</tt> or
<tt>nslookup</tt> for these tests! They bypass the NSS and thus
<tt>nss-mdns</tt> and issue their DNS queries directly.) </p>
<p>If you run a firewall, don't forget to allow UDP traffic to the the
mDNS multicast address <tt>224.0.0.251</tt> on port 5353.</p>
<p>Starting with version 0.5, <tt>nss-mdns</tt> has a simple
configuration file <tt>/etc/mdns.allow</tt> for enabling name lookups
via mDNS in other domains than <tt>.local</tt>. The file contains
valid domain suffixes, seperated by newlines. Empty lines are ignored
as are comments starting with #. To enable mDNS lookups of all names,
regardless of the domain suffix add a line consisting of <tt>*</tt>
only (similar to <tt>nss-mdns</tt> mode of operation of versions <= 0.4):</p>
<pre># /etc/mdns.allow
*</pre>
<p>If the configuration file is absent or unreadable
<tt>nss-mdns</tt> behaves as if a configuration file with the following
contents is read: </p>
<pre># /etc/mdns.allow
.local.
.local</pre>
<p>i.e. only hostnames ending with <tt>.local</tt> are resolved via
mDNS.</p>
<p>If the configuration file is existent but empty, mDNS name lookups
are disabled completely.</p>
<h2><a name="requirements">Requirements</a></h2>
<p>Currently, <tt>nss-mdns</tt> is tested on Linux only. A fairly
modern <tt>glibc</tt> installation with development headers (2.0 or
newer) is required. Not suprisingly <tt>nss-mdns</tt> requires a
kernel compiled with IPv4 multicasting support enabled.</p>
<p><tt>nss-mdns</tt> was developed and tested on Debian GNU/Linux
"testing" from December 2004, it should work on most other Linux
distributions (and maybe Unix versions) since it uses GNU autoconf and
GNU libtool for source code configuration and shared library
management.</p>
<h2><a name="installation">Installation</a></h2>
<p>As this package is made with the GNU autotools you should run
<tt>./configure</tt> inside the distribution directory for configuring
the source tree. After that you should run <tt>make</tt> for
compilation and <tt>make install</tt> (as root) for installation of
<tt>nss-mdns</tt>.</p>
<h2><a name="acks">Acknowledgements</a></h2>
<p>SHIROYAMA Takayuki, Anand Kumria and Bastien Nocera for patches.</p>
<p>Sean Meiners for search list support.</p>
<p>Philipp Zabel for ARM support.</p>
<h2><a name="download">Download</a></h2>
<p>The newest release is always available from <a href="@PACKAGE_URL@">@PACKAGE_URL@</a></p>
<p>The current release is <a href="@PACKAGE_URL@nss-mdns-@PACKAGE_VERSION@.tar.gz">@PACKAGE_VERSION@</a></p>
<p>Get <tt>nss-mdns</tt>'s development sources from the <a href="http://subversion.tigris.org/">Subversion</a> <a href="svn://svn.0pointer.de/nss-mdns">repository</a> (<a href="http://0pointer.de/cgi-bin/viewcvs.cgi/?root=nss-mdns">viewcvs</a>): </p>
<pre>svn checkout svn://svn.0pointer.de/nss-mdns/trunk nss-mdns</pre>
<p>You may find an up to date Debian package of <tt>nss-mdns</tt> on the <a href="http://packages.debian.org/libnss-mdns">Debian package repository</a>. Many other distributions ship it, too.</p>
<p>If you want to be notified whenever I release a new version of this software use the subscription feature of <a href="http://freshmeat.net/projects/nss-mdns/">Freshmeat</a>.</p>
<hr/>
<address class="grey">Lennart Poettering <@PACKAGE_BUGREPORT@>, April 2006</address>
<div class="grey"><i>$Id$</i></div>
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