China Telecom China Telecom CERNET Center/Tsinghua University Verizon Inc Orange Swisscom For the IPv6 transition, dual-stack deployments require both IPv4 and IPv6 forwarding capabilities to be deployed in parallel. IPv6-only is considered as the ultimate stage where only IPv6 transfer capabilities are used while ensuring global reachability for both IPv6 and IPv4 (usually known as IPv4aaS). This document specifies requirements and proposes a framework for deploying IPv6-only as the underlay in multi-domain networks, discusses the requirements of service traffic, major components and interfaces, IPv6 mapping prefix allocation, typical procedures for service delivery. The document also discusses related considerations with security.