[c-nsp] Please help clarify bus/fabric terminology on the 6500/7600

[Gert Doering]

Hi,

On Fri, Nov 06, 2009 at 04:15:39AM -0800, Rick Ernst wrote:
> - The 32Gbs bus is shared and the PFC on the sup does the forwarding

Yes.

> - The switch fabric is on the Sup; DFC cards use the fabric, others use the
> PFC

Not exactly.  Fabric-enabled cards will always use the fabric to transport
the packets directly to the destination line card.  If the card has no DFC,
it will use the bus(!) to do the destination lookup via the Sup PFC.

(I'm a bit unclear on how fabric-only cards transport packets to bus-only
cards, tho).

> - If I happen to install a 256K DFC in a 1M TCAM system, can the DFC be
> forced off; 1M TCAM via the 32Gbs bus?

As far as I know, no.  If you have no DFC, you need a CFC on the card.

> - The 32Gbs bus and 20Gbs fabric are total capacity; could you push
> 1Gbs/31Gbs on the 32Gbs bus?

Hmmm?

> - Design considerations need to include Sup level, PFC, DFC, 32Gbs shared,
> 8gbs/20Gbs fabric

Yes.  If you have enough traffic that it matters...

> >From a practical viewpoint, I'm currently pushing a little less than ~800Mbs
> in+out at about 120Kpps. It's getting to be too much for my current software
> forwarding, especially during D/DoS.  A Sup720-3BXL gives me 1M routes in
> TCAM, and 15Gbs/30Mpps forwarding in the PFC. Control-plane and data-plane
> separation, with data-plane in hardware. I could use any combination of line
> cards and still be significantly ahead of my current utilization.  As the
> bits get bigger and faster, I can offload forwarding onto DFC-enabled cards,
> but I'd need to start with DFCs that also have the large TCAM, otherwise
> I'm  still using the 32Gbs bus and the PFC.

Yes.

> For D/DoS purposes, policing is handled in hardware at the port ASIC.  If a
> 1Gbs-connected network were to go nuts and was throttled to 1Mbs, neither
> the bus nor fabric would see the .99Gbs?

I think this depends on card type.  A bus-only card has no other way to
decide what to do with the packet than "put it on the bus".

On a fabric/CFC card, you'll see the headers on the bus, but not the packets.

A DFC card will drop the packet right away.

(I might be mistaken here)

gert

-- 
USENET is *not* the non-clickable part of WWW!
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Gert Doering - Munich, Germany                             gert at greenie.muc.de
fax: +49-89-35655025                        gert at net.informatik.tu-muenchen.de
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