The dns64perf++ DNS64 benchmarking program is the world’s first standard DNS64 benchmarking tool, which complies with the compulsory requirements of RFC 8219 on benchmarking methodology for IPv6 transition technologies including DNS64. The aim of our current effort is to enable dns64perf++ for benchmarking the caching performance of DNS64 servers, which was qualified as optional by the RFC, but can be important in practice, and thus make dns64perf++ the world’s first standard DNS64 benchmarking tool that provides all the features described in the RFC. In this paper, we disclose our goals, design considerations as well as implementation decisions. We also provide a simple case study to demonstrate the operability of the new feature.