On Tue, Nov 04, 1997 at 06:59:45PM -0800, Jonathan Stone wrote:
> "Heiko W.Rupp" <hwr@pilhuhn.de> writes:
> >Yes and no. IP can do it for you. But if the card has already the possibility
> >to filter out packets that no one wants, then there is less work to do at
> >IP-layer.
> Sorry, that's completely incorrect, as I explained in my original message.

No it is not.

> The IPv4 mapping from class D addresses to Ethernet link-level
> multicast addreses is a a many-to-one mapping.  Ethernet hardware

Yes. 

> filters only on the Ethernet link-level addresses.  So the IP level
> software *has* to check that the class-D addresses it receives are in

Yes. That's what I am saying.

But you must tell your card somehow to not only listen to its unicast
address.
You can do this on two ways - program it to receive some multicast
adresses or - programm it to receive all packets. 
The only thing I was saying is, that in the latter case, IP has to
do much more work than in the former case, so it is imho a necessity
that the card already filters out multicast adresses, which can't be
received (say if the group 224.0.1.2 is requested and if the hash for 
224.0.1.2 gives 224.x.1.2 then there is no need to also pass 224.x.2.y
to the IP-layer).

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