Vagrant: 3 machines in private network

Vagrantfile

Vagrant.configure("2") do |config|

  config.vm.define "lb" do |lb|
    lb.vm.box = "centos65"
    lb.vm.host_name = "lb"
    lb.vm.network "private_network", ip: "192.168.0.20"
    lb.vm.network :forwarded_port, guest: 22, host: 2220, id: "ssh", auto_correct: true
    lb.vm.network :forwarded_port, guest: 80, host: 9099, id: "web", auto_correct: true
    config.vm.provider :virtualbox do |vb|
      vb.customize ["modifyvm", :id, "--memory", "512"]
    end
  end

  config.vm.define "i1" do |i1|
    i1.vm.box = "centos65"
    i1.vm.host_name = "i1"
    i1.vm.network "private_network", ip: "192.168.0.21"
    i1.vm.network :forwarded_port, guest: 22, host: 2221, id: "ssh", auto_correct: true
    config.vm.provider :virtualbox do |vb|
      vb.customize ["modifyvm", :id, "--memory", "1024"]
    end
  end

  config.vm.define "i2" do |i2|
    i2.vm.box = "centos65"
    i2.vm.host_name = "i2"
    i2.vm.network "private_network", ip: "192.168.0.22"
    i2.vm.network :forwarded_port, guest: 22, host: 2222, id: "ssh", auto_correct: true
    config.vm.provider :virtualbox do |vb|
      vb.customize ["modifyvm", :id, "--memory", "1024"]
    end
  end

end