In the preceding diagram, three interfaces are cabled to each host. The eth0 interface will serve as the management interface for OpenStack services and API access. The eth1 interface will be used for overlay network traffic between hosts. On the controller node, eth2 will be used for external network traffic to instances through Neutron routers. If VLAN tenant networks are used in lieu of overlay networks such as VXLAN and GRE, then eth2 will be configured on the compute nodes to support those networks.
At a minimum, the management interface should be configured with an IP address that has outbound access to the Internet. Internet access is required to download OpenStack packages from the Ubuntu package repository. Inbound access to the management address of the servers from a trusted network via SSH (TCP port
22) is recommended.