Using Hiera for subnet based decisions in puppet 3.0.x

192.168.1.0.yaml

# in /etc/puppet/hieradata/
---
someclass::setting1: 'blah'
someclass::another_setting: 1234
someclass::array_setting:
  - 'oneval'
  - 'twoval'
  - 'redval'
  - 'blueval'

hiera.yaml

---
:hierarchy:
  - %{network_eth0}
  - common

:backends:
  - yaml

:yaml:
  :datadir: '/etc/puppet/hieradata'

someclass.pp

class someclass(
  $setting1 = 'sane_default',
  $another_setting = 'also sane default',
  $array_setting = [],
) {

  #puppet code using those variables...
}