HowToZeroconf

Revision 4 as of 2006-04-29 10:57:28

Clear message

[http://www.zeroconf.org/ Zeroconf] is a collection of tools and protocols to allow networks to configure themselves. It is called Bonjour (formerly Rendezvous) by Apple, and used extensively on Mac OS X.

Zeroconf consists of

  • Name resolution, MDNS
  • Service Advertising
  • Address allocation

Traditionally most of its work is done by DHCP and DNS. But the decentralised zeroconf method is appropriate is some situations, for example ad-hoc networks. It also requires no configuration (apart from the installation).

It works happily along side traditional tools. For example you may have an IP address allocated by DHCP and use DNS to resolve address on the web, but still use the hostname.local from MDNS to resolve the addresses of other computer on the LAN.

Note, if you are not doing this on your own network you may want to talk to the Network Admin first. Although zeroconf is a fairly efficient protocol the admin may not want the extra traffic. Also be aware that it is trivially easy to spoof an mdns .local name.

Installation

Dapper Drake

Just install the package avahi-daemon using Synaptic (See SynapticHowto), or run 

sudo apt-get install avahi-daemon

Breezy Badger and Hoary Hedgehog

If you are running ubuntu 5.04 (Hoary) then you will need to use mdnsresponder instead of avahi.

To start using Zeroconf you need to install libnss-mdns and avahi on each computer. These are both in the universe, and can be installed with synaptic or a quick 

sudo apt-get install libnss-mdns avahi-daemon

Now you need to enable mdns name resolution. This is controlled by the file 

/etc/nsswitch.conf

Find the line 

hosts:       files dns

and change it to 

hosts:       files dns mdns4

Make sure you do this on each computer.

MDNS

Now each computer with avahi-daemon (mdnsresponder on hoary) installed will identify its self on the network as 

hostname.local

for example, my computer flute, identifies itself as 

flute.local

Now any computer on the network can use hostname.local in place of an ip address. For example you can do 

ping flute.local

or 

ssh flute.local

PowerPC problem on Hoary

libnss-mdns 0.3 is broken on big-endian systems such as PowerPC ( https://bugzilla.ubuntu.com/show_bug.cgi?id=10912 ). However the problem is fixed with version 0.4. Either upgrade to [BreeezyBadger] or download the source from http://0pointer.de/lennart/projects/nss-mdns/ and build it.

Firewall configuration

If you are running a fire wall and you are having problems like 

sam@titania:~$ ping flute.local
ping: unknown host flute.local

then it is possible that your firewall is blocking the zeroconf communication. If you can turn your firewall off and this fixes the problem, then it is definitely the firewall.

http://0pointer.de/lennart/projects/nss-mdns/ advises to "allow UDP traffic to the the mDNS multicast address 224.0.0.251 on port 5353."

If you are using [Firestarter] all multicast traffic is blocked. This may be configurable in the next version. The current work around is to edit 

/etc/firestarter/firewall

You will need to chmod u+x this file to make it writable.

Find the section 

# Block Multicast Traffic
#  Some cable/DSL providers require their clients to accept multicast transmissions
#  you should remove the following four rules if you are affected by multicasting
$IPT -A INPUT -s 224.0.0.0/8 -d 0/0 -j DROP
$IPT -A INPUT -s 0/0 -d 224.0.0.0/8 -j DROP
$IPT -A OUTPUT -s 224.0.0.0/8 -d 0/0 -j DROP
$IPT -A OUTPUT -s 0/0 -d 224.0.0.0/8 -j DROP

and comment out the 4 lines 

# Block Multicast Traffic
#  Some cable/DSL providers require their clients to accept multicast transmissions
#  you should remove the following four rules if you are affected by multicasting
#$IPT -A INPUT -s 224.0.0.0/8 -d 0/0 -j DROP
#$IPT -A INPUT -s 0/0 -d 224.0.0.0/8 -j DROP
#$IPT -A OUTPUT -s 224.0.0.0/8 -d 0/0 -j DROP
#$IPT -A OUTPUT -s 0/0 -d 224.0.0.0/8 -j DROP

Then restart firestarter 

sudo /etc/init.d/firestarter restart

Now you should be able to resolve .local names. 

sam@titania:~$ ping flute.local
PING flute.local (192.168.1.101) 56(84) bytes of data.
64 bytes from flute.local (192.168.1.101): icmp_seq=1 ttl=64 time=4.45 ms
64 bytes from flute.local (192.168.1.101): icmp_seq=2 ttl=64 time=4.16 ms

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