17.3.2 Different Versions
The internet group management protocol comes is different versions: IGMPv0,IGMPv1,and IGMPv2.
The first version(IGMPv0) is outdated [Deer86] and no longer used,so we won't discuss it here.
The successor version(IGMPv1) is specified in RFC 1112 and fully implemented in the Linux kernel.
This version defines two protocol messages, which can be distinguished by contents of the type field: