Re: [DLC]Multicast

Thanks John... of course by "handling IGMP" I thought I had eluded to
IGMP snooping and (*eek* CGMP).  As a personal rule, vendor specific
protocols that 'assist' or 'replace' other standards; are typically
not a good choice to make.

--
Matthew P Kemp



On Mon, Mar 15, 2010 at 2:39 PM, John Kristoff <[email protected]> wrote:
> On Mon, Mar 15, 2010 at 01:58:46PM -0500, Matthew P Kemp wrote:
>>   Typically when you look at multicast you are looking at the routers
>> (unless the switch is handling IGMP), the switch typically treat
>> multi-cast traffic as if were a broadcast.  The Ethernet card is just
>
> Depending on the switch, it may support something generically called
> IGMP snooping, which means the switch will try IP multicast packets
> a bit differently than broadcast.  With snooping, the switch will
> forward group messages only to ports that have expressly indicated
> interest in the group with a IGMP message.  Cisco switches also have
> something called CGMP.  There has been a history of potential issues
> with IGMP snooping.  Basically anytime you start forcing your so-called
> L2 device to start examining L3 or higher info, things get tricky.  For
> example, there was a problem with Cisco switches flooding multicast
> (basically like a broadcast storm) whenever there was a spanning tree
> topology change.  In large-use streaming multicast environments, that
> would cause all sorts of reliability and performance issues.
>
> John
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