单项选择题 Which enhancement w as added to IGMP version 3?（）

单项选择题 When building an IP multicast domain using PIM which mode assumes that other routers do not want to forward multicast packets for the group?（）

多项选择题 In IPv6 network, an IPv6 overlay tunnel is required to communicate with isolated IPv6 networks across the existing IPv4 infrastructurE. There are currently fiv e IPv6 overlay tunnel types. Which three IPv6 overlay tunnel statements are true？（）