Ruby-on-rails – Rails 4.2 Server port forwarding on Vagrant does not work

I have a Vagrant VM with Rails installed with a sample app. The VM is configured to forward the port 3000 (of Rails Webrick server) to my host 3000 port.

config.vm.network "forwarded_port", guest: 3000, host: 3000

Everything is configured as seen in a lot of examples.

But, when I try to access http://localhost:3000 nothing happens. I've also tried to forward to other random ports like 8081, 25600, without success. Doing a curl request also does not get anything (just a Connection reset by the peer message), and a curl request inside VM works perfectly (as expected).

Both my PC and my VM runs Ubuntu 12.04. I'm using Ruby 2.2.0 and Rails 4.2.0.

An important point is that Apache works normally. I forwarded the port 80 to port 8080 and everything works. It seems that the problem is just with the Rails server, even if when I use other ports (rails server -p 4000, for example)