Much work has been done on IPv6 standards and many IPv6 test beds have been deployed. However, little is known about the performance of the real IPv6 Internet, especially from the perspective of end users. In this paper, the authors perform a case study of current IPv6 performance from CERNET. They propose an active measurement methodology, which analyzes the traces of file transference from IPv4/IPv6 dual-stack Web servers. They study 936 dual-stack Web servers located in 44 countries by collecting and analyzing over 585,680 IPv4/IPv6 packet-level traces with 133,340 million packets.