[c-nsp] DCEF720 card together with CEF256/classic line cards in Cat6.5k with Sup720?

[Brian Turnbow]

HI Lars,

> -----Original Message-----
> From: Lars Fenneberg [mailto:lf at elemental.net]
> Sent: sabato 22 settembre 2012 11:20
> To: Brian Turnbow
> Cc: cisco-nsp at puck.nether.net
> Subject: Re: [c-nsp] DCEF720 card together with CEF256/classic line cards
> in Cat6.5k with Sup720?
> 
> Hey Brian,
> 
> Quoting Brian Turnbow (b.turnbow at twt.it):
> 
> > > Is a DCEF720 card like the WS-X6708-10G-3CXL supported together with
> > > a Supervisor 720 and a bunch of classic and CEF256 line cards?
> >
> > Short answer yes, long answer is that mixing dfc cards brings
> limitations, all dfcsgoing to lowest common denominator, OIR etc.
> 
> thanks for your answer. I'm not so much concerned about mixing different
> revisions of PFC/DFCs as the supervisor engine has a PFC3BXL so it'll fall
> back to 3BXL which is okay.  

You will go to the lowest DFC for all dfc and pfc, so one dfca will bring all the box down, both dfc and pfc.

I'm thinking about the packet flow in such a
> scenario: Is the forwarding decision made on the DFC and the packet is
> then transfered via the switching fabric to the supervisor which then puts
> it on the bus? So the supervisor is just used as a gateway from the
> switching fabric to the bus?
> 

Packet switching is done by the incoming engine, so DFC if you have one.
In the case of mixed dfcs/classic card you will be in truncated mode where only headers will be sent to sup for dfc to dfc traffic with the data via fabric and full packet is sent across the bus when going to a classic card. You are limited to 15Mpps mixing cards but can get more bandwidth pushed through than with only classic cards.
I don't really know if the pfc then does a lookup as well in this case though. Maybe one of the experts here can chime in !


Regards

Brian

> I've found several presentations on the topic [1] but they don't talk
> about the DCEF/classic combination.
> 
> Cheers,
> Lars
> 
> [1] http://www.scribd.com/doc/21695833/Cisco-Catalyst-6500-Switch-
> Architecture
> --
> Lars Fenneberg, lf at elemental.net (private), lf at mcs.de (work) Work
> legalese: MCS Moorbek Computer Systeme GmbH, Hamburg, Handelsregister
> Hamburg B62933, Geschaeftsfuehrer: Kai Brandes, Eckard Kabel


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