Single source can transmit multiple group in multicast

Question

single source can transmit multiple group in a multicast domain

Answer 1

I am not sure how to start explaining this, but I will give it a try to my understanding.
1)
Look up the MAC Learning section in this link.
http://www.ciscopress.com/articles/article.asp?p=101367&rl=1
2)
Once you have read through then your question would be if switches deliver traffic based on mac address of the end hosts, how is this mapping achieved for multicast addresses, as they are not assigned to any host.
in this case the switch will consider the multicast packet as unknown as will broadcast it. To avoid that a simple mechanism of multicast
IP to mac conversion was introduced which would create these temporary mac's based on the membership report of end hosts
for a certain group. So when this conversion is done apart from the real host mac address pointing to the port where it is connected,
multicast mac also points to the same port. Based on which the switch is able to forward the traffic intelligently to a set of hosts
who want that group received.
3)
Now see this link which explains how Mcast IP to MAC convesion is done.
IP to MAC Conversion
http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/ipmulti.htm#wp1020628
To summarize this, since only 23 bits are available for converting the IP to MAC, the 24th bit is lost .
which in terms of binary to decimal means you have lost 128 from the decimal. so it loops from the start of the multicast range of 224-239 at every 128 bits.
if the starting decimal was 224.1.1.1(if the received membership report was for 224.1.1.1) then next would be 224.129.1.1, 225.1.1.1 , 225.129.1.1 and so on till 239.......
hence when it loops through all the 224 - 239 addres range and it catches up 32 mapped addresses.
Now to conclude,
"32 IP multicast addresses corresponding to each MAC " In here the MAC referenced is not the host mac but the converted MAC.
Even though the conversion is done, because of the available bits the MAC address hence created overlaps 32 multicast IP
addresses. (closest resemblence would be the ACL example with the mask assigned. based on this mask and the starting value
it will keep catching values based on the mask. )
You can try this practically. Assume you have a host and it sends a membership report for 225.10.10.10. Now the switch has to convert this to Mcast MAC.
To do this yourself, write down the binary of this address, and look at the rightmost 23 bits (that is from the left ignore the first 9 binary values.) now if you look at the remaining binary values, these will map and look alike for 226.10.10.10 226.139.10.10 and so on. And hence if you run through from 224-239 you will get 32 adresses.
HTH-Cheers,
Swaroop