Когда я запускаю vagrant up, я получаю:
D:\GitHub\website\rails-dev-box>vagrant up
Bringing machine 'default' up with 'virtualbox' provider...
==> default: Checking if box 'ubuntu/trusty32' is up to date...
==> default: Clearing any previously set forwarded ports...
==> default: Clearing any previously set network interfaces...
==> default: Preparing network interfaces based on configuration...
default: Adapter 1: nat
==> default: Forwarding ports...
default: 3000 => 1234 (adapter 1)
default: 22 => 2222 (adapter 1)
==> default: Booting VM...
==> default: Waiting for machine to boot. This may take a few minutes...
default: SSH address: 127.0.0.1:2222
default: SSH username: vagrant
default: SSH auth method: private key
default: Warning: Connection timeout. Retrying...
default: Warning: Remote connection disconnect. Retrying...
default: Warning: Remote connection disconnect. Retrying...
default: Warning: Remote connection disconnect. Retrying...
default: Warning: Remote connection disconnect. Retrying...
default: Warning: Remote connection disconnect. Retrying...
default: Warning: Remote connection disconnect. Retrying...
default: Warning: Remote connection disconnect. Retrying...
Это предупреждение будет навсегда.
Я заметил, что если я запустил виртуальную машину вручную (без бродяг), она будет работать без каких-либо задержек, но только если я включил адаптер 2 в настройках VM следующим образом: 
Как включить адаптер 2 виртуальной машины при использовании vagrant up?
ИЗМЕНИТЬ
Vagrantfile:
# -*- mode: ruby -*-
# vi: set ft=ruby :
Vagrant::Config.run do |config|
# config.vm.network :hostonly, "192.168.50.4"
end
Vagrant.configure('2') do |config|
config.vm.box = 'ubuntu/trusty32'
config.vm.hostname = 'rails-dev-box'
# config.vm.synced_folder ".", "/vagrant/web" #, type: "nfs"
config.vm.provider :virtualbox do |vb|
vb.gui = true
end
config.vm.boot_timeout = 120
# config.winnfsd.uid = 1
# config.winnfsd.gid = 1
config.vm.network :forwarded_port, guest: 3000, host: 1234
config.vm.provision :shell, path: 'bootstrap.sh', keep_color: true
end