mDNS: Bonjour Slackware

Bonjour Sourire by Henri Salvador

"Adieu tristesse, bonjour sourire" - Henri Salvador

Goodbye sadness, hello smile. Somehow it seems apt.

For 20 years now I have used static IP rather than a Name Server for my home network. When I started my home network, computers were expensive and few. But then came the Raspberry Pi and the Espressif ESP8266.

In practice I maintained a 'name server' by hand, updating my /etc/resolv.conf every time I added a new computer to the network. There are now over 100 entries in 3 sub-nets but you do get used to it. What put me over the edge was the IoT device.

The need for periodic security updates meant reprogramming: the device had to be taken down and the ESP8266 plugged into its programmer. The most useful ones always seem to be the most inaccessible, like upside down on the ceiling or out in the elements like the autogate controller.

Then along came Over The Air programming, just like you would update your App in your smartphone. But now every IoT device came with its unique static IP address, while I might have 10 IoT lights installed, there is only 1 version source code and there was a high chance I would brick a device by using the wrong address.

But adieu tristesse, there is mDNS or Multicast DNS to the rescue. mDNS was first implemented as Apple Inc's Bonjour. Actually I unknowingly used it in ArduinoOTA and Raspbian. It is just my main workstations ran Slackware, which did not come with mDNS pre-installed. It would be nice to update IoT devices directly from my development machine.

To install mDNS onto my Slackware 14.2-current (which does not automatically resolve dependencies) you will need to install in this order: libdaemon, avahi and  nss-mdns.

But first you need to create the user 'avahi':

$groupadd -g 214 avahi

$useradd -u 214 -g 214 -c "Avahi User" -d /dev/null -s /bin/false avahi

libdaemon:

$tar -xvpzf libdaemon.tar.gz

$cd libdaemon

Download the source code libdaemon-0.14.tar.gz into libdaemon directory and:

$./libdaemon.SlackBuild

which produced /tmp/libdaemon-0.14-x86_64-1_SBo.tgz and can be installed into Slackware thus:

$upgradepkg --install-new /tmp/libdaemon-0.14-x86_64-1_SBo.tgz

avahi:

$tar -xvpzf avahi.tar.gz

$cd avahi

Download your source code

$ ./avahi.SlackBuild

$upgradepkg --install-new /tmp/avahi-0.7-x86_64-1_SBo.tgz

In my case I ring-fenced my IoT devices in their own WiFi Access Point. Many consumer WiFi routers (like my TP-Link TL-MR3420) randomly drops connections to the WiFi clients when there are too many of them, like around 30 devices.

This means my Slackware server (ie Google smart home nodejs, MQTT, and webhook servers) can only access the IoT devices from behind their router. In this case I had to set just one of the mDNS computers in the IoT subnet to reflector. That is in /etc/avahi/avahi-daemon.conf add:

[reflector]
enable-reflector=yes
  

$/etc/rc.d/rc.avahidaemon start

Starting Avahi mDNS/DNS-SD Daemon:  /usr/sbin/avahi-daemon -D

$/etc/rc.d/rc.avahidnsconfd start

Add the following lines to your /etc/rc.d/rc.local:

# Start avahidaemon

if [ -x /etc/rc.d/rc.avahidaemon ]; then

  /etc/rc.d/rc.avahidaemon start

fi

# Start avahidnsconfd

if [ -x /etc/rc.d/rc.avahidnsconfd ]; then

  /etc/rc.d/rc.avahidnsconfd start

fi

nss-mdns:

$tar -xvzf nss-mdns.tar.gz

$cd nss-mdns

Download your source code

$./nss-mdns.SlackBuild

$upgradepkg --install-new /tmp/nss-mdns-0.10-x86_64-2_SBo.tgz

Now your  /etc/nsswitch.conf will have a line line this:

hosts:          files dns

Which you need to change to 

hosts:          files mdns4_minimal [NOTFOUND=return] dns

After which a command like getent will work:

$getent hosts MyComputer.local

123.45.67.89   MyComputer.local

And you should be able to remotely access it by name without a DNS server:

$ssh -t MyComputer.local

Even better, it works with the ArduinoOTA code for the ESP8266. This sets me up nicely for Over The Air software upgrades for my home-brew IoT devices. 

Pour éclairer un ciel trop gris,
Pour cueillir un bout de printemps
Il suffit dans la vie
Il suffit bien souvent
De dire adieu tristesse, bonjour sourire.

Happy Trails.

To illuminate a sky too gray,
To pick a piece of spring
It's enough in life
It is often enough
To say goodbye sadness, hello smile.