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Similar to the customer / service provider network model that exists in the Internet today, the Department of Defense's (DoD's) Global Information Grid (GIG) will consist of various customer networks (Army, Navy, etc.) that interconnect over a common core. Customer networks will source and sink IP traffic, and a transit network(s) will provide connectivity between geographically disparate customer networks. As networks within the GIG begin to transition from the Internet Protocol version 4 (IPv4) to IPv6, three different types of networks will emerge: IPv6-only, IPv4-only, and dual-stack (IPv4 and IPv6). These three network types will appear in both GIG customer networks and transit networks. Interconnecting hosts across these heterogeneous networks presents various routing and forwarding challenges. For example, a transit network that supports a single address family (e.g., IPv6) cannot forward packets for customers that are of a different address family (e.g., IPv4). Therefore, a mechanism that allows the transit network to forward an unsupported address family is needed. This paper reviews new mechanisms that are being developed in the Internet Engineering Task Force (IETF) Softwires Working Group (WG) and proposes to leverage these mechanisms to solve several GIG routing problems. Applied to the GIG, a softwire-based architecture can be used by IPv6-only core networks to transport customer IPv4 traffic, and IPv4-only core networks to transport customer IPv6 traffic. In addition, the application of softwires to enable "prefix tracking" for IP security (IPsec)-protected encInternet Engineering Task Force (IETF) Softwires Working Grouplaves is discussed.