||As software defined networking (SDN) can become a key technique for the control of individual coalition networks of a software defined coalition (SDC), the interconnection of such networks can become a major challenge. Traditional approaches such as BGP to interconnect autonomous networks are designed for less flexible networks and hence can have serious efficiency and flexibility issues. In this short paper, we define the requirements of the interconnection of such networks and provide an overview of a novel protocol, called the SDC-Network Federation Protocol (SFP). Instead of being a traditional push protocol such as BGP, SFP adopts a novel pub-sub model to substantially increase efficiency and flexibility. Going beyond only packet handling, SFP introduces flexible network information spaces, such as the packet space and the flowset space.