First, we must understand how the IGMP membership query works,
since this is the question that starts the entire group management process.
The source address of the query is the router on the
segment which is the Globomantics router,
R1.
The destination of IGMP queries is always 224.0 .0 .1,
which is the all hosts link local multicast address.
The easiest way to understand this message is to think of the question,
who wants multicast?
That is what the query is really asking.
The type of the message is 11 in hex or 17 in decimal.
Wireshark knows this is a version 1 query because the code is
set to 0 shown as reserved in the capture.
We will see how IGMP version 2 recycles this field to convey
additional information in a future clip.
The multicast address is always 0.0 .0 .0 in these membership queries,
since IGMPv1 has no mechanism for group-specific queries.
While IGMPv1 is relatively weak compared to its successors,
it is a very simple protocol with only 2 messages that did work well for its day.