[求教] 400-101题库中Q178的原答案有不同意见

liubin0521

An IPv6 network has different MTUs on different segments, if the network is experiencing reliability issues, which option is
the most likely reason?
A. ICMPv6 is filtered.
B. The Do Not Fragment bit is marked.
C. HSRPv6 is configured incorrectly.
D. The MTU size is greater than 1470 bytes.  

原答案选的是B，但是ipv6没有DF位啊？ 此题选A如何，请大神指教，提前谢过。