Add example zeroconf configuration using Avahi.

Thanks to BrainDamage for providing this example.

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+[[!meta title="zeroconf IP and DNS configuration"]]
+
+## Example: zeroconf IP and DNS configuration
+
+This example describes how to setup a network with no centralized dhcp server
+and automatic dns resolution and minimum configuration:
+
+You will need Avahi mDNS daemon up and running (not part of this guide,
+please refer to your distro): [http://avahi.org/](http://avahi.org/)
+
+### Setting up Avahi hostname resolution:
+
+This will allow your computer to resolve mDNS hostnames which addresses in the form of something.local.
+In order to do it,
+edit `/etc/nsswitch.conf` and append `mdns_minimal [NOTFOUND=return]` to your `hosts:` line before your `dns` entry,
+for example my configuration is:
+
+       hosts: files myhostname mdns_minimal [NOTFOUND=return] dns
+
+(Note that you can use a different top level domain than .local,
+but in such case you need to use `mdns` entry instead of `mdns_minimal`.)
+
+### Automatic ip assignment and network setup:
+
+Follow the "how to configure" guide from the [[docs|manual]] to create the key pair and folders,
+then edit `tinc.conf` and insert `Mode = switch`,
+this will allow to make all nodes to listen to the same subnet mask simplifying the configuration
+(although it'll increase traffic since all nodes will get the data).
+By default the subnet mask is 169.254.0.0/16.
+We'll change how `tinc-up` brings up the VPN interface; instead of using `ifconfig` to bring up the interface,
+we'll use `avahi-autoipd daemon`.
+This yields many advantages:
+
+* autoipd daemon automatically assignes an ip address based off available pool
+* it'll publish the hostname in the mdns resolution network and will also act as controller for the avahi daemon allowing to browse or publish avahi services
+
+So in the `tinc-up` script you'll have a line like: `avahi-autoipd -D $INTERFACE`.
+That's it! your VPN will have auto assigned IP addresses, and automatically resolved DNS entries once it's up.
+In order to list the machines on the network you can use this command: `avahi-browse -d networkname`.
+
+### Useful bits:
+
+You can insert static hostname resolution for VPN nodes using `/etc/avahi/hosts` much like `/etc/hosts`.
+You can manually ask for preferred IP when calling `avahi-autoipd` by appending `-S` <i>wantedip</i>.
+
+### Example configuration:
+
+In my configuration I have a PC everything connects to (alarmpi, reachable at LAN address 192.168.1.12 and public address alarmpi.xyz.com), and a laptop and a phone that can access it.
+
+Alarmpi's `tinc.conf`:
+
+       Name = alarmpi
+       Mode = switch
+
+The laptop's `tinc.conf`:
+
+       ConnectTo = alarmpi
+       Name = laptop
+       Mode = switch
+
+The phone's `tinc.conf`:
+
+       ConnectTo = alarmpi
+       Name = phone
+       Mode = switch
+
+Every node has the same `tinc-up:`
+
+       #!/bin/sh
+       avahi-autoipd -D $INTERFACE
+
+`hosts/alarmpi`:
+
+       Address = 192.168.1.12
+       Address = alarmpi.xyz.com
+       
+       -----BEGIN RSA PUBLIC KEY-----
+       snip
+       -----END RSA PUBLIC KEY-----
+
+`hosts/laptop`:
+
+       -----BEGIN RSA PUBLIC KEY-----
+       snip
+       -----END RSA PUBLIC KEY-----
+
+`hosts/phone`:
+
+       -----BEGIN RSA PUBLIC KEY-----
+       snip
+       -----END RSA PUBLIC KEY-----