Re: Switches and Multicast doubt

One other thing I wanted to add -- Just because a switch treats L2 broadcast
and multicast essentially the same (forwarding the frame out all ports
except the one it came in on) does not mean it cannot differentiate between
the two. As somebody else noted, there are separate counters for broadcast,
multicast, and other things like storm control seem to differentiate between
the two.

On Wed, Sep 28, 2011 at 11:47 AM, Joe Astorino <joeastorino1982_at_gmail.com>wrote:

> 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
>>
>>
>> Blogs and organic groups at http://www.ccie.net
>>
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>>
>>
>>
>>
>>
>
>
> --
> Regards,
>
> Joe Astorino
> CCIE #24347
> Blog: http://astorinonetworks.com
>
> "He not busy being born is busy dying" - Dylan
>
>

-- 
Regards,
Joe Astorino
CCIE #24347
Blog: http://astorinonetworks.com
"He not busy being born is busy dying" - Dylan
Blogs and organic groups at http://www.ccie.net