require 'facter'
require 'ipaddr'

Facter.add('revzone') do
  setcode do
    ip = Facter.value(:networking)['ip6']
    cidr = IPAddr.new("::/#{Facter.value(:networking)['netmask6']}").prefix
    addr = IPAddr.new ip
    parts = addr.ip6_arpa.split('.')
    parts.drop(cidr/4).join('.')
  end
end