[openib-general] RDMA CM multicast

[Andrew Friedley]

Michael S. Tsirkin wrote:
>> What would be needed is a way for the user to indicate that they need a unique
>> address.  An obvious way to accomplish this is for the user to specify an IP
>> address of 0.0.0.0 when calling rdma_join_multicast().  The user would first
>> need to bind to a specific device by calling rdma_bind_addr() with a local IP
>> address.
> 
> Is this how it works with sockets?

I'm not aware of IP multicast having this functionality.  This is a 
major problem with IP multicast, as some sort of address selection 
arbitration has to be done.  From what I've seen, this ranges from IANA 
assigning multicast addresses for specific uses to best-effort protocols 
for selecting unused addresses from an available range.  It's a fairly 
hard problem, and having OFED choose an unused address (my understanding 
is that the SM is capable of this) sidesteps the issue and makes life 
much better.

Andrew