Re: Switches and Multicast doubt

Still i find two different interface counters for broadcast and multicast.
How does the switch internally differentiate the multicast and broadcast. If
IGMP snooping is enabled , the switch the snoop the packets going from
router to the host .
And it updates in its MAC table about the multicast MAC address and the
corresponding interface. How does the switch look into the frame and update
in its MAC table. Can anyone explain me the procedure. I am confused?
THank you

On Wed, Sep 28, 2011 at 10:13 PM, Scott Morris <swm_at_emanon.com> wrote:

> At Layer2, the difference is subtle. At Layer3, it's different! As
> others pointed out, 01:00:5E will lead every IP multicast packet at
> Layer2 (it's all about the handoff to higher functions in the switch).
>
> Any other Layer2 "group" address which does not have specific code
> attached to it will be replicated to all devices in that broadcast domain.
>
> There are many group addresses though, that DO have other code to
> intercept... Spanning Tree is an L2 multicast address.... CDP is...
> Just to name a couple!
>
> It's all about awareness though. if the switch isn't aware, it will
> flood the frame. The PC then is presumed to be aware of whether it's
> part of that group or not.
>
> HTH,
>
> Scott
>
>
>
>
> *Scott Morris*, CCIE/x4/ (R&S/ISP-Dial/Security/Service Provider) #4713,
>
> CCDE #2009::D, CCNP-Voice, JNCIE-SP #153, JNCIE-ER #102, CISSP, et al.
>
> CCSI #21903, JNCI-SP, JNCI-ER
>
> swm_at_emanon.com
>
>
> Knowledge is power.
>
> Power corrupts.
>
> Study hard and be Eeeeviiiil......
>
>
> On 9/28/11 11:10 AM, CCIE KID wrote:
> > Hi fellas,
> >
> > I have a million dollar doubt. Whether switches understand multicast or
> not.
> > Its all about the so called I/G bit setting in the MAC frame. If the I
> bit
> > is set to 1 then its a multicast address . But unfortunately the
> broadcast
> > address also has the I bit set to 1 . So how does a switch differentiate
> > multicast and broadcast. Is there any method used in cisco switches to
> > differentiate. Can anyone help me out?
>
>
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