Create external network, and its associated subnet:
# Source the admin tenant credentials
$ . keystonerc_admin
$ keystone tenant-list | grep services | awk '{print $2;}'
3e112abc4c4b4214b8efbd627a32f75e
$ neutron net-create --tenant-id 3e112abc4c4b4214b8efbd627a32f75e \
ext --router:external=True