CERNET2 is the biggest IPv6-only network in the world and one of the China Next Generation Internet (CNGI) backbones. In order to evaluate and choose the best core routers for these core nodes, we tested all the core routers based on both our IPv6 Protocol Integrated Test System (PITS) and AX4000 (invented by Spirent Company). The paper first briefly introduces IPv6, ICMPv6 and Path MTU protocols and the conformance testing methodology, including the IPv6 PITS, test architectures and test suites. After testing all the core routers, it thoroughly analyzes experimental results of IPv6, ICMPv6 and Path MTU protocols separately. In the analysis, the paper depicts important errors found in protocol implementations and designs, and proposes valuable suggestions to them. Besides, the paper also classifies and summarizes all the errors.