I followed OpenStack Installation Guide for Ubuntu 14.04(http://docs.openstack.org/kilo/install-guide/install/apt/content/ (http://docs.openstack.org/kilo/instal...)) step-by-step from chapter 1 to 6 (using neutron with 3 nodes).

However, after I launched an instance (chapter 12), I'm unable to ping http://openstack.org from that instance like the example in the 'To access your instance using a virtual console' section (http://docs.openstack.org/kilo/install-guide/install/apt/content/launch-instance-neutron.html#d6e4570 (http://docs.openstack.org/kilo/instal...)):

Verify the ext-net external network:

$ ping -c 4 openstack.org
PING openstack.org (174.143.194.225) 56(84) bytes of data.
64 bytes from 174.143.194.225: icmp_req=1 ttl=53 time=17.4 ms
64 bytes from 174.143.194.225: icmp_req=2 ttl=53 time=17.5 ms
64 bytes from 174.143.194.225: icmp_req=3 ttl=53 time=17.7 ms
64 bytes from 174.143.194.225: icmp_req=4 ttl=53 time=17.5 ms

--- openstack.org ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 3003ms
rtt min/avg/max/mdev = 17.431/17.575/17.734/0.143 ms

Here is my result:

$ ping -c 4 openstack.org
ping: bad address 'openstack.org'

And I'm quite sure that I didn't miss a thing about configuring dns servers. Every hosts can ping http://openstack.org normally.