4 Copyright 2004-2007 Lennart Poettering <mzaffzqaf (at) 0pointer (dot)
18 This program is free software; you can redistribute it and/or modify
19 it under the terms of the GNU Lesser General Public License as
20 published by the Free Software Foundation; either version 2 of the
21 License, or (at your option) any later version.
23 This program is distributed in the hope that it will be useful, but
24 WITHOUT ANY WARRANTY; without even the implied warranty of
25 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
26 Lesser General Public License for more details.
28 You should have received a copy of the GNU Lesser General Public
29 License along with this program; if not, write to the Free Software
30 Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
36 [10]Version 0.10 released. Changes include: Ported to FreeBSD;
37 alignment fixes for SPARC.
41 [11]Version 0.9 released. Changes include: Make most shared library
42 symbols private to not conflict with any symbols of the program we're
43 loaded into. Fix a potential endless loop in the mDNS packet parsing
46 Please note that due to security reasons from this release on the
47 minimal mDNS stack included in nss-mdns (dubbed "legacy") is no longer
48 built by default. Thus, nss-mdns will not work unless [12]Avahi is
49 running! That makes Avahi essentially a hard dependency of nss-mdns.
50 Pass --enable-legacy to reenable the mini mDNS stack again. Please
51 note as well that this release does not honour /etc/resolv.conf domain
52 search lists by default anymore. It created a lot of problems and was
53 never recommended anyway. You may reenable this functionality by
54 passing --enable-search-domains.
58 [13]Version 0.8 released. Changes include: Build time option to
59 disable "legacy unicast" mDNS requests, i.e. resolve exclusively with
60 Avahi; build a special _minimal flavour of the shared objects to
61 minimize unnecessary name lookup timeouts; fix IPv6 resolving when
64 Please note that starting with nss-mdns 0.8 we encourage you to use a
65 different /etc/nsswitch.conf configuration line. See below for more
70 [14]Version 0.7 released. Changes include: Portability patch for ARM
71 from Philipp Zabel; make sure not to print any messages to STDERR;
72 deal with OOM situations properly; if multiple addresses are assigned
73 to the same interface make sure to send a query packet only once;
78 [15]Version 0.6 released. Changes include: honour search list in
79 /etc/resolv.conf; try to contact [16]Avahi for resolving.
83 [17]Version 0.5 released. Changes include: only lookup hostnames
84 ending in .local; add support for a configuration file
85 (/etc/mdns.allow) to allow lookups for other names.
89 [18]Version 0.4 released. Changes include: small portability fix for
90 big endian architectures; send "legacy unicast" packets instead of
91 normal mDNS packets (this should reduce traffic and improve response
96 [19]Version 0.3 released. Changes include: add Debianization; use
97 ip6.arpa instead of ip6.int for reverse IPv6 lookups.
101 [20]Version 0.2 released. Changes include: send mDNS queries on every
102 interface that supports multicasts, instead of only the one with the
103 default route, making nss-mdns more robust on multi-homed hosts; gcc
108 [21]Version 0.1 released
112 nss-mdns is a plugin for the GNU Name Service Switch (NSS)
113 functionality of the GNU C Library (glibc) providing host name
114 resolution via [22]Multicast DNS (aka Zeroconf, aka Apple Rendezvous,
115 aka Apple Bonjour), effectively allowing name resolution by common
116 Unix/Linux programs in the ad-hoc mDNS domain .local.
118 nss-mdns provides client functionality only, which means that you have
119 to run a mDNS responder daemon seperately from nss-mdns if you want to
120 register the local host name via mDNS. I recommend [23]Avahi.
122 nss-mdns is very lightweight (9 KByte stripped binary .so compiled
123 with -DNDEBUG=1 -Os on i386, gcc 4.0), has no dependencies besides the
124 glibc and requires only minimal configuration.
126 By default nss-mdns tries to contact a running [24]avahi-daemon for
127 resolving host names and addresses and making use of its superior
128 record cacheing. Optionally nss-mdns can be compiled with a mini mDNS
129 stack that can be used to resolve host names without a local Avahi
130 installation. Both Avahi support and this mini mDNS stack are
131 optional, however at least one of them needs to be enabled. If both
132 are enabled a connection to Avahi is tried first, and if that fails
133 the mini mDNS stack is used.
139 If the mini MDNS stack is used, nss-mdns supports resolving IPv6
140 addresses but does so via IPv4 multicasts only. If Avahi is used for
141 resolving IPv6 is supported properly.
145 After compiling and installing nss-mdns you'll find six new NSS
150 * libnss_mdns_minimal.so.2
151 * libnss_mdns4_minimal.so.2
152 * libnss_mdns6_minimal.so.2
154 libnss_mdns.so.2 resolves both IPv6 and IPv4 addresses,
155 libnss_mdns4.so.2 only IPv4 addresses and libnss_mdns6.so.2 only IPv6
156 addresses. Due to the fact that most mDNS responders only register
157 local IPv4 addresses via mDNS, most people will want to use
158 libnss_mdns4.so.2 exclusively. Using libnss_mdns.so.2 or
159 libnss_mdns6.so.2 in such a situation causes long timeouts when
160 resolving hosts since most modern Unix/Linux applications check for
161 IPv6 addresses first, followed by a lookup for IPv4.
163 libnss_mdns{4,6,}_minimal.so (new in version 0.8) is mostly identical
164 to the versions without _minimal. However, they differ in one way. The
165 minimal versions will always deny to resolve host names that don't end
166 in .local or addresses that aren't in the range 169.254.x.x (the range
167 used by [25]IPV4LL/APIPA/RFC3927.) Combining the _minimal and the
168 normal NSS modules allows us to make mDNS authoritative for Zeroconf
169 host names and addresses (and thus creating no extra burden on DNS
170 servers with always failing requests) and use it as fallback for
173 To activate one of the NSS modules you have to edit /etc/nsswitch.conf
174 and add mdns4 and mdns4_minimal (resp. mdns, mdns6) to the line
175 starting with "hosts:". On Debian this looks like this:
182 hosts: files mdns4_minimal [NOTFOUND=return] dns mdns4
192 That's it. You should now be able to resolve hosts from the .local
193 domain with all your applications. For a quick check use glibc's
195 $ getent hosts foo.local
196 192.168.50.4 foo.local
198 Replace foo whith a host name that has been registered with an mDNS
199 responder. (Don't try to use the tools host or nslookup for these
200 tests! They bypass the NSS and thus nss-mdns and issue their DNS
203 If you run a firewall, don't forget to allow UDP traffic to the the
204 mDNS multicast address 224.0.0.251 on port 5353.
206 Please note: The line above makes nss-mdns authoritative for the
207 .local domain. If you have a unicast DNS domain with the same name you
208 will no longer be able to resolve hosts from it. mDNS and a unicast
209 DNS domain named .local are inherently incompatible. Please contact
210 your local admistrator and ask him to move to a different domain name
211 since .local is to be used exclusively for Zeroconf technology.
212 [26]Further information.
214 Starting with version 0.5, nss-mdns has a simple configuration file
215 /etc/mdns.allow for enabling name lookups via mDNS in other domains
216 than .local. The file contains valid domain suffixes, seperated by
217 newlines. Empty lines are ignored as are comments starting with #. To
218 enable mDNS lookups of all names, regardless of the domain suffix add
219 a line consisting of * only (similar to nss-mdns mode of operation of
224 If the configuration file is absent or unreadable nss-mdns behaves as
225 if a configuration file with the following contents is read:
230 i.e. only hostnames ending with .local are resolved via mDNS.
232 If the configuration file is existent but empty, mDNS name lookups are
233 disabled completely. Please note that usually mDNS is not used for
234 anything but .local, hence you usually don't want to touch this file.
238 Currently, nss-mdns is tested on Linux only. A fairly modern glibc
239 installation with development headers (2.0 or newer) is required. Not
240 suprisingly nss-mdns requires a kernel compiled with IPv4 multicasting
241 support enabled. [27]Avahi is recommended for its superior cacheing
242 capabilities and for security reasons. Unless you compile nss-mdns
243 with --enable-legacy Avahi is a hard dependency when nss-mdns is used,
244 however not a build-time requirement.
246 nss-mdns was developed and tested on Debian GNU/Linux "testing" from
247 December 2004, it should work on most other Linux distributions (and
248 maybe Unix versions) since it uses GNU autoconf and GNU libtool for
249 source code configuration and shared library management.
253 As this package is made with the GNU autotools you should run
254 ./configure inside the distribution directory for configuring the
255 source tree. After that you should run make for compilation and make
256 install (as root) for installation of nss-mdns.
260 SHIROYAMA Takayuki, Anand Kumria and Bastien Nocera, Sjoerd Simons for
263 Sean Meiners for search list support.
265 Philipp Zabel for ARM support.
267 Bruce M Simpson for porting it to FreeBSD.
271 The newest release is always available from
272 [28]http://0pointer.de/lennart/projects/nss-mdns/
274 The current release is [29]0.10
276 Get nss-mdns's development sources from the [30]Subversion
277 [31]repository ([32]viewcvs):
278 svn checkout svn://svn.0pointer.de/nss-mdns/trunk nss-mdns
280 You may find an up to date Debian package of nss-mdns on the
281 [33]Debian package repository. Many other distributions ship it, too.
283 If you want to be notified whenever I release a new version of this
284 software use the subscription feature of [34]Freshmeat.
285 _________________________________________________________________
288 Lennart Poettering <mzaffzqaf (at) 0pointer (dot) de>, May 2007
290 $Id: README.html.in 116 2007-05-12 14:54:24Z lennart $
298 5. README#documentation
299 6. README#requirements
300 7. README#installation
303 10. http://0pointer.de/lennart/projects/nss-mdns/nss-mdns-0.10.tar.gz
304 11. http://0pointer.de/lennart/projects/nss-mdns/nss-mdns-0.9.tar.gz
305 12. http://avahi.org/
306 13. http://0pointer.de/lennart/projects/nss-mdns/nss-mdns-0.8.tar.gz
307 14. http://0pointer.de/lennart/projects/nss-mdns/nss-mdns-0.7.tar.gz
308 15. http://0pointer.de/lennart/projects/nss-mdns/nss-mdns-0.6.tar.gz
309 16. http://avahi.org/
310 17. http://0pointer.de/lennart/projects/nss-mdns/nss-mdns-0.5.tar.gz
311 18. http://0pointer.de/lennart/projects/nss-mdns/nss-mdns-0.4.tar.gz
312 19. http://0pointer.de/lennart/projects/nss-mdns/nss-mdns-0.3.tar.gz
313 20. http://0pointer.de/lennart/projects/nss-mdns/nss-mdns-0.2.tar.gz
314 21. http://0pointer.de/lennart/projects/nss-mdns/nss-mdns-0.1.tar.gz
315 22. http://www.multicastdns.org/
316 23. http://avahi.org/
317 24. http://avahi.org/
318 25. http://files.zeroconf.org/rfc3927.txt
319 26. http://avahi.org/wiki/AvahiAndUnicastDotLocal
320 27. http://avahi.org/
321 28. http://0pointer.de/lennart/projects/nss-mdns/
322 29. http://0pointer.de/lennart/projects/nss-mdns/nss-mdns-0.10.tar.gz
323 30. http://subversion.tigris.org/
324 31. svn://svn.0pointer.de/nss-mdns
325 32. http://0pointer.de/cgi-bin/viewcvs.cgi/?root=nss-mdns
326 33. http://packages.debian.org/libnss-mdns
327 34. http://freshmeat.net/projects/nss-mdns/