Is Current 6to4 Relay Deployment Adequate?

6to4 is a mechanism for providing IPv6 connectivity where native IPv6 is still unavailable. 6to4 is based on relay routers deployment. The anycast technique is used to address relays, and each relay's advertisement may be seen globally or only within a limited scope. The number of available relays is important to this mechanism's robustness, as well as their geographic location. Due to the details of the mechanism, limited scope relays are not easy to find, despite the fact their location and existence is key to evaluate suitability of current deployment.