http://www.rfc-editor.org/rfc/rfc7598.txt
RFC 7598: DHCPv6 Options for Configuration of Softwire Address and Port-Mapped Clients, T. Mrugalski, O. Troan, I. Farrer, S. Perreault, W. Dec, C. Bao, L. Yeh, X. Deng2015-07-01T23:00:00-00:00This document specifies DHCPv6 options, termed Softwire46 options, for the provisioning of Softwire46 Customer Edge (CE) devices. Softwire46 is a collective term used to refer to architectures based on the notion of IPv4 Address plus Port (A+P) for providing IPv4 connectivity across an IPv6 network.