[c-nsp] Multicast source question

[Michael Robson]

In trying to troubleshoot a multicast problem, I have discovered that I
don't fully understand part of the multicast process and so would be
grateful if I could get an answer to the following. When a client streams
traffic out to a multicast group, I had assumed that it would treat the
traffic as any other unicast traffic in that it would see the destination IP
as outside its subnet (i.e. a CLass D address) and so send it onto its
gateway (with the source and destination MAC at the layer 2 being set to the
server and router MACs respectively) - no IGMP joining happens because it is
a source only. Is this true, or does the server set the destination MAC to
the multicast MAC that corresponds to the multicast IP (which an ethereal
capture seems to be suggesting)? If this is true, then what is the process
that gets the stream to the router, i.e. how does the switch determine that
it should add the corresponding multicast MAC to the port facing the router?

Could any answers please be copied to my direct email as well as the list,
as I only get digests.


Thanks,

Michael.
--
Michael Robson,           | Tel:  0161 275 6113
Networks,                 | Fax:  0161 275 6040
University of Manchester. | Email: Michael.Robson at manchester.ac.uk

Youth and skill are no match for experience and treachery.