Re: IP layer and layer 2 IGMP Snooping

On Jun 8, 9:57 pm, Albert Manfredi <bert22...@xxxxxxxxxxx> wrote:
On Jun 7, 1:28 am, vicky <vikrant.pan...@xxxxxxxxx> wrote:

     What is the difference in

                                 IP Layer IGMP Snooping  and,
                                 Layer 2 IGMP Snooping.

Wait, I think I know what this is referring to.

When doing IGMP snooping, the L2 switch can use the IP address of the
IGMP join messages to derive the MAC multicast address, then use the
MAC multicast address of the arriving data frames to make forwarding
decisions. This is the more "classic" approach. Or the L2 switch can
use the IP address of the arriving UDP/IP datagrams to make the
forwarding decision, and never bother using the MAC multicast address
at all.

Perhaps this is what the terminology is referring to. Using the IP
address to make forwarding decisions is actually preferable, because
28 bits of an IPv4 multicast address determine the multicast group.
When mapped to the MAC address, only 23 bits are used to differentiate
IPv4 multicast groups at the MAC layer, so there is some ambiguity as
to what MAC hosts really want the multicast.

Bert

-----------------------------------------------------
Ok Mr. Bert

As u written that there may be some ambiguty when (Multicast)IP to
Mac resolution
Is this ambiguity is
for example there are two multicast ip addresses

224.1.1.3 - 01-00-5e-01-01-03
225.1.1.3 - 01-00-5e-01-01-03

these represent 2 different multicast group.

Now when it resoluted to ip-mac for multicast table entry in l 2
switch as well as to come at DA of multicast packet.

then
how a switch can able to differentiate the two multicast ranges
(224.1.1.3 and 225.1.1.3 )

please tell me ....................

Thanks

Vikrant
.

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