Vagrant, setting multiple IPs on a box

The official doc gives example only for 1 IP: http://docs.vagrantup.com/v2/networking/private_network.html

Vagrant.configure("2") do |config|
  config.vm.network "private_network", ip: "192.168.50.4"
end

Googling around I could find only 1 example of Multiple IPs:

https://groups.google.com/forum/#!topic/vagrant-up/hqtdOEjjlsw

Vagrant::Config.run do |config|
  config.vm.define :web001 do |config|
    config.vm.box = "base"
    config.vm.forward_port("http", 5000, 8881)
    config.vm.forward_port("ssh", 22, 2222)
    config.vm.host_name = "web001.example.com"
    config.vm.network("33.33.33.10")
    config.vm.network("33.33.33.20", {:adapter=>2})
  end
end 

but it doesn't work for me...

Any help would be greatly appreciated....