What is 6RD (IPv6 Rapid Deployment on IPv4 infrastructures)?

It is a mechanism to facilitate IPv6 rapid deployment across the IPv4 infrastructures. IPv6 rapid deployment on IPv4 infrastructures builds on mechanisms of 6 to 4 to enable a service provider so that it can rapidly deploy IPv6 unicast service to IPv4 sites to which it provides CPE (Customer Premise equipment). It utilizes stateless IPv6 in IPv4 encapsulation in order to transit IPv4-only network infrastructure. The advantages of this approach are that it requires no modification to customer premise equipment and avoids the assignment of IPv4 addresses to customer equipment. 6RD is a reference to both the rapid deployments of IPv6.