Connecting OpenStack instances directly to an external network with Neutron

Issue

• I need to create some instances and connect them directly to an external network and use an external default gateway for those instances. I should still be able to add other instances to private tenant networks isolated using gre or vxlan or vlan and route them to different external networks using floating IPs via neutron virtual router. Is it possible to connect an instance directly to an external network using openvswitch plugin?
• How do I configure external networks in OpenStack
• We have a fresh install of openstack from packstack, and we need to configure neutron to use vlans.
• After a fresh installation of packstack, how do we setup neutron to use a provider network for external traffic?