I am running Ubuntu inside vagrant, here is the Vagrantfile:
# Vagrantfile API/syntax version. Don\'t touch unless you know what you\'re doing! VAGRANTFILE_API_V
I can bet you're looking at eth0 (that's another interface). Look at eth1 and you'll get what you're searching for. Moreover, from outside vagrant, try to ping it with
eth0
eth1
ping 192.168.99.4