
                                 nss-mdns 0.6

   Copyright 2004,2005 Lennart Poettering <mzaffzqaf (at) 0pointer (dot)
   de>
     * [1]License
     * [2]News
     * [3]Overview
     * [4]Status
     * [5]Documentation
     * [6]Requirements
     * [7]Installation
     * [8]Acknowledgements
     * [9]Download

License

   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.

   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.

   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.

News

   Sun Aug 21 2005:

   [10]Version 0.6 released. Changes include: honour search list in
   /etc/resolv.conf; try to contact [11]Avahi for resolving.

   Sat Jun 4 2005:

   [12]Version 0.5 released. Changes include: only lookup hostnames
   ending in .local; add support for a configuration file
   (/etc/mdns.allow) to allow lookups for other names.

   Sun May 15 2005:

   [13]Version 0.4 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)

   Jan Sun 16 2005:

   [14]Version 0.3 released. Changes include: add Debianization; use
   ip6.arpa instead of ip6.int for reverse IPv6 lookups.

   Fri Dec 17 2004:

   [15]Version 0.2 released. Changes include: send mDNS queries on every
   interface that supports multicasts, instead of only the one with the
   default route, making nss-mdns more robust on multi-homed hosts; gcc
   2.95 compatiblity.

   Mon Dec 6 2004:

   [16]Version 0.1 released

Overview

   nss-mdns is a plugin for the GNU Name Service Switch (NSS)
   functionality of the GNU C Library (glibc) providing host name
   resolution via [17]Multicast DNS (aka Zeroconf, aka Apple Rendezvous),
   effectively allowing name resolution by common Unix/Linux programs in
   the ad-hoc mDNS domain .local.

   nss-mdns provides client functionality only, which means that you have
   to run a mDNS responder daemon seperately from nss-mdns if you want to
   register the local host name via mDNS (e.g. [18]Avahi).

   nss-mdns is very lightweight (23 KByte stripped binary .so compiled
   with -DNDEBUG=1 on i386, gcc 3.3), has no dependencies besides the
   glibc and requires only minimal configuration.

   Optionally, nss-mdns can try to contact a running [19]avahi-daemon to
   make use of its superior record cacheing.

Current Status

   It works!

   While nss-mdns supports resolving IPv6 addresses it does so via IPv4
   multicasts only.

Documentation

   After compiling and installing nss-mdns you'll find three new NSS
   modules in /lib:
     * libnss_mdns.so.2
     * libnss_mdns4.so.2
     * libnss_mdns6.so.2

   libnss_mdns.so.2 resolves both IPv6 and IPv4 addresses,
   libnss_mdns4.so.2 only IPv4 addresses and libnss_mdns6.so.2 only IPv6
   addresses. Due to the fact that most mDNS responders only register
   local IPv4 addresses via mDNS, most people will want to use
   libnss_mdns4.so.2 exclusively. Using libnss_mdns.so.2 or
   libnss_mdns6.so.2 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.

   To activate one of the NSS modules you have to edit /etc/nsswitch.conf
   and add mdns4 (resp. mdns, mdns6) to the line starting with "hosts:".
   On Debian this looks like this:
# /etc/nsswitch.conf

passwd:         compat
group:          compat
shadow:         compat

hosts:          files dns mdns4
networks:       files

protocols:      db files
services:       db files
ethers:         db files
rpc:            db files

netgroup:       nis

   That's it. You should now be able to resolve hosts from the .local
   domain with all your applications. For a quick check use glibc's
   getent tool:
$ getent hosts foo.local
192.168.50.4    foo.local

   Replace foo whith a host name that has been registered with an mDNS
   responder.

   To reduce the traffic nss-mdns is responsible for consider installing
   glibc's name service cache daemon nscd. However, when doing
   troubleshooting for nss-mdns, don't forget to disable nscd for getting
   sensible results.

   If you run a firewall, don't forget to allow UDP traffic to the the
   mDNS multicast address 224.0.0.251 on port 5353.

   Starting with version 0.5, nss-mdns has a simple configuration file
   /etc/mdns.allow for enabling name lookups via mDNS in other domains
   than .local. 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 * only (similar to nss-mdns mode of operation of
   versions <= 0.4):
# /etc/mdns.allow
*

   If the configuration file is absent or unreadable nss-mdns behaves as
   if a configuration file with the following contents is read:
# /etc/mdns.allow
.local.
.local

   i.e. only hostnames ending with .local are resolved via mDNS.

   If the configuration file is existent but empty, mDNS name lookups are
   disabled completely.

   nss-mdns does not honour the domain search list of /etc/resolv.conf,
   because I don't consider that this would be a good idea, since every
   name lookup for non-existing domains would result in a series of long
   timeouts of nss-mdns. If somebody still considers this a good idea, he
   is free to send me a sensible patch, which I might apply, but only if
   the domain search list may be disabled.

Requirements

   Currently, nss-mdns is tested on Linux only. A fairly modern glibc
   installation with development headers (2.0 or newer) is required. Not
   suprisingly nss-mdns requires a kernel compiled with IPv4 multicasting
   support enabled.

   nss-mdns 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.

Installation

   As this package is made with the GNU autotools you should run
   ./configure inside the distribution directory for configuring the
   source tree. After that you should run make for compilation and make
   install (as root) for installation of nss-mdns.

Acknowledgements

   SHIROYAMA Takayuki for a patch.

   Sean Meiners for search list support.

Download

   The newest release is always available from
   [20]http://0pointer.de/lennart/projects/nss-mdns/

   The current release is [21]0.6

   Get nss-mdns's development sources from the [22]Subversion
   [23]repository ([24]viewcvs):
svn checkout svn://svn.0pointer.de/nss-mdns/trunk nss-mdns

   You may find an up to date Debian package of nss-mdns on the
   [25]Debian package repository.

   If you want to be notified whenever I release a new version of this
   software use the subscription feature of [26]Freshmeat.
     _________________________________________________________________


    Lennart Poettering <mzaffzqaf (at) 0pointer (dot) de>, Aug 2005

   $Id: README.html.in 83 2005-08-21 21:49:30Z lennart $

References

   1. README#license
   2. README#news
   3. README#overview
   4. README#status
   5. README#documentation
   6. README#requirements
   7. README#installation
   8. README#acks
   9. README#download
  10. http://0pointer.de/lennart/projects/nss-mdns/nss-mdns-0.6.tar.gz
  11. http://www.freedesktop.org/Software/Avahi
  12. http://0pointer.de/lennart/projects/nss-mdns/nss-mdns-0.5.tar.gz
  13. http://0pointer.de/lennart/projects/nss-mdns/nss-mdns-0.4.tar.gz
  14. http://0pointer.de/lennart/projects/nss-mdns/nss-mdns-0.3.tar.gz
  15. http://0pointer.de/lennart/projects/nss-mdns/nss-mdns-0.2.tar.gz
  16. http://0pointer.de/lennart/projects/nss-mdns/nss-mdns-0.1.tar.gz
  17. http://www.multicastdns.org/
  18. http://www.freedesktop.org/Software/Avahi
  19. http://www.freedesktop.org/Software/Avahi
  20. http://0pointer.de/lennart/projects/nss-mdns/
  21. http://0pointer.de/lennart/projects/nss-mdns/nss-mdns-0.6.tar.gz
  22. http://subversion.tigris.org/
  23. svn://svn.0pointer.de/nss-mdns
  24. http://0pointer.de/cgi-bin/viewcvs.cgi/?root=nss-mdns
  25. http://packages.debian.org/libnss-mdns
  26. http://freshmeat.net/projects/nss-mdns/
