Re: Switches and Multicast doubt

At the most basic level, without any Cisco magic a switch does the same
thing with a multicast as it does with a broadcast frame -- forwards it out
every port on the VLAN except the one it came in on.

Now, that sort of defeats the purpose of multicast at a L2 level so ... in
comes IGMP snooping, which is enabled by default. That way, a switch can
determine exactly what switch ports have hosts connected that have joined a
particular multicast group, and it can send the frames out only to those
devices as necessary

Additionally, Multicast at an L2 Ethernet level is defined by the range
01:00:5e:00:00:00 - 01:00:5e:7f:ff:ff. IANA owns the 24-bit OUI 01:00:5e.
The 25th MSB is always 0, and that leaves 23 bits for actual multicasting

HTH

On Wed, Sep 28, 2011 at 11:10 AM, CCIE KID <eliteccie_at_gmail.com> 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?
>
> --
> With Warmest Regards,
>
> CCIE KID
> CCIE#29992 Security
>
>
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-- 
Regards,
Joe Astorino
CCIE #24347
Blog: http://astorinonetworks.com
"He not busy being born is busy dying" - Dylan
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