multicasting question

hi everyone,

I'm new to the forum (great site by the way).

I've got a couple of questions regarding multicasting. I've read the explanation on this site, but it does not state of how to join a group.

Also if you join a certain group, can you also receive packets from other groups or do you have to join those groups too? Because from what I understand if your datalink layer recognizes multicast packets, does this not mean that it can receive packets from all groups?

thx in advance for your answers!

I am new to the subject of multicasting too, but I believe you would have to join each group individually. If not, I wouldn't see the point of having groups, you would simply have accept multicast or don't. I also think there is a range of groups or something that happens due to the IP to MAC mapping.

Yes, you will have to join each multicast group individually.
Because of the IP to MAC mapping, 32 different multicast groups (IP's) are mapped on the same MAC address, so when a multicast frame is received, the host's IP layer must check whether he is really interested in receiving that multicast packet(i.e. has joined the group). If not, then that packet must be discarded.

Thanks,
Datacom_guy.