[openib-general] Re: ipoib send-only join to IGMP multicast group

[Roland Dreier]

    Jack> 1. Why is this a send-only join? Is this just so that the
    Jack> local host to "announce" itself to a router (for neighbor
    Jack> calculations)?

Because the kernel has asked the IPoIB driver to send a packet to this
group, but has not asked the IPoIB driver to start 

    Jack> 2. Who is responsible for creating this multicast group in
    Jack> IPoIB? (A send-only join will not cause a group to be
    Jack> created if it does not yet exist)

The group will be created if any full-member joins are done.  But that
won't happen unless some entity wants to receive packets from the
group -- in other words, some multicast router.

 - R.