IP Multicast over Ethernet

Hello, every one.
 I have just completed reading "interconnections" By
Radia Perlman (an excellent book ), but one thing
seems unclear to me. This is regarding how IP and
Ethernet multicast cooperate. I was hoping that
somebody in this learned list would be able to resolve
the confusions that plague my mind. I have the
following questions regarding IP Multicast over
Ethernet Multicast:

1) I know that the lower 23 bits of MAC address are
copied from the lower three bytes of IP Multicast
address. But my question is: how does the NIC or
device driver ever know that this particular packet is
to be multicast? is there something like a *flag* in a
generic API call that tells the multicast address to
be chosen. I have tried to study some of the
sock_opt() in Linux but this behavior is not
explicitly visible.

Also how can/does the NIC hardware differ b/w
multicast and broadcast address. The nic cant figure
out just on the basis of the dest MAC multicast
address that this host belongs to the group or not.

2)The following scenario is what has bothered me a lot

  ++++   ++++ ++++      +++++     Internet   ++++
  + A+   + B+ + C+      + GW+----------------+ D+ 
  ++++   ++++ ++++      +++++                ++++

RE: IP Multicast over Ethernet

> Hello, every one.
>  I have just completed reading "interconnections" By
> Radia Perlman (an excellent book ), but one thing
> seems unclear to me. This is regarding how IP and
> Ethernet multicast cooperate. I was hoping that

Let me recommend you another great book: UNIX Network Programming, 2nd Edition, vol.1, by Richard W.
Stevens. This book solves all problems you have exposed in your query.

--
Miguel Angel Rodriguez Jodar | http://icaro.eii.us.es
Area de Arquitectura y Tecnologia de Computadores
Universidad de Sevilla

RE: IP Multicast over Ethernet

Affan

A host that subscribes to a IPMC group address will receive, at the MAC
layer, all groups that correspond to that layer 2 address. As the data
gram progresses up the hosts stack the frame is striped and the layer 3
address is read, the host will discard those packets that are not to the
group address it has subscribed too.

The GW if its is IP Multicast enabled, i.e running PIM or some such,
will receive ALL multicast traffic and forward only those it needs to,
as determined by it Multicast routing protocol.

I also answered inline

Hope this helps

Bryan

> -----Original Message-----
> From: Affan Ahmed [mailto:intiha <at> yahoo.com] 
> Sent: 12 August 2002 10:37
> To: magma <at> ietf.org
> Subject: [magma] IP Multicast over Ethernet
> 
> 
> Hello, every one.
>  I have just completed reading "interconnections" By
> Radia Perlman (an excellent book ), but one thing
> seems unclear to me. This is regarding how IP and
> Ethernet multicast cooperate. I was hoping that

[Fwd: Mailman upgrade at ietf.org]

MAGMA'ers,
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Regards,
Brian

From: Mail Administrator <mailadm <at> ietf.org>
Subject: Mailman upgrade at ietf.org
Date: 2002-08-19 17:27:28 GMT

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