Subject: Re: Use of SAP in a PIM SSM Network

From: Bill Fenner <[email-masked]>
Date: Sat, 25 Nov 2000 11:05:55 -0800

From my hallway discussions about MAC-layer collisions, I think the fear
is that the light switch will join the ALL-LIGHT-SWITCHES group, and if
that happens to collide at the MAC layer with a 25Mbps video stream the
light switch's CPU will be too busy dropping traffic to turn the light on.
Only a layer 3 device could save the light switch, since a layer 2 device
(even an IGMP-snooping one) can still only filter on the MAC address.

  Bill

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From: Mark Handley <[email-masked]>
Date: Sat, 25 Nov 2000 11:58:34 -0800

>(even an IGMP-snooping one) can still only filter on the MAC address.

In almost all cases, having IP-aware NICs seems to be a bad thing in
the long run.  This might just be one of those rare cases when it
isn't.

If multicast ever becomes common enough for this to be a real problem,
I'd think this would be a point on which products can differentiate
themselves.

Cheers,
	Mark

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From: Beau Williamson <[email-masked]>
Date: Mon, 27 Nov 2000 11:52:38 -0800

>I'd think this would be a point on which products can differentiate

Exactly.

I personally think that IGMPv3 should be clear signal to switch designers that tomorrow's switches will not be able to make forwarding decisions solely at the MAC layer as they have in the past.  Instead, they will need to maintain more L3 state in order to perform their tasks efficiently.

Beau Williamson