Multi-domain software-defined networks (SDN) require controllers of different domains to be inter-connected to share their available intra-domain paths for inter-domain routing. This specific network of connections, called inter-domain control network, is somewhat similar to a signaling network. Provisioning flow-paths across multiple domains with certain service levels requires information on availability of resources and capabilities along data paths. A quality of service (QoS), or a reliable and secure path service requires a data path with certain quantitative service level requirements such as high throughput, low packet loss, or high availability. This paper outlines the inter-domain control network capabilities with emphasis on what information can be realistically shared in real-time amongst SDN controllers. It also describes the information that can be stored in global databases to enable an autonomous decision making in data path selection for flows.