It is expected that future tactical warfighting functions, such as tactical picture management and sensor tasking, will be distributed applications running on different systems, connected via a network. Recently, an air force fifth generation network has been proposed where airborne networks are linked with other domains to form a multi-domain network supporting a combat cloud. There are many challenges in building such networks. We propose in this paper a software-defined multi-domain network (SD-DMN) architecture that provides resilient multi-domain networks. Our proposed architecture consists of a software defined communication system to integrate multiple bearers and a Border Gateway Protocol (BGP) control plane for connectivity, traffic and policy management. Using this unique architecture, we develop an algorithm provides multiple reliable transmission paths between any two nodes. Network emulation experiments have been conducted using the Mininet emulation software. The Mininet experiments and prototype implementation validate the feasibility of our proposals.