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Posted by vicky on June 11, 2008, 2:55 am
>
>
>
>
>
>
> > > =A0 =A0 =A0What is the difference in
>
> > > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0IP =
Layer IGMP Snooping =A0and,
> > > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0Lay=
er 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 =A0when (Multicast)IP to
> Mac resolution
> Is this ambiguity is
> for example there are two multicast ip addresses
>
> 224.1.1.3 =A0- =A0 01-00-5e-01-01-03
> 225.1.1.3 =A0- =A0 01-00-5e-01-01-03
>
> these represent 2 different multicast group.
>
> Now when it resoluted to =A0ip-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 =A0and =A0 225.1.1.3 )
>
> please tell me ....................
>
> Thanks
>
> Vikrant- Hide quoted text -
>
> - Show quoted text -
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One more thing i want to ask
Is the Multicast IP to mac resolution is done at host pc's end also.
to make a multicast MAC address
For exp
if multicast ip address is
227.2.3.7
then its mac address
01-00-5e-02-03-07
is made at host pc end , as then it send packet by setting this mac
address to the DA field.
Vikrant
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