IETF RFC 6674 PDF

Gateway-Initiated Dual-Stack Lite (GI-DS-Lite) is a variant of Dual- Stack Lite (DS-Lite) applicable to certain tunnel-based access architectures. GI-DS-Lite extends existing access tunnels beyond the access gateway to an IPv4-IPv4 NAT using softwires with an embedded Context Identifier that uniquely identifies the end-system to which the tunneled packets belong. The access gateway determines which portion of the traffic requires NAT using local policies and sends/ receives this portion to/from this softwire.