[c-nsp] N7K fabric behavior

Tim Stevenson tstevens at cisco.com
Thu Dec 8 12:10:19 EST 2011

Hi Tim, please see inline below:

At 08:35 AM 12/8/2011, Tim Durack submitted:

>Trying to get something clear in my mind:
>N7K, 2x FAB-2, fabric redundancy, 220G capacity.
>N7K, 3x FAB-2, fabric redundancy, 330G capacity.
>N7K, 5x FAB-2, fabric redundancy, 550G capacity.
>Cisco recommend a minimum of 3 FAB-2 cards. Why?

The origin of this recommendation is around M1 10G modules, which are 
80G/slot cards. So 2 fabrics give you full b/w & the 3rd gives you 
N+1 redundancy. This rule however doesn't apply to some of the higher 
performing cards (F1, F2).

>If I choose to ignore this recommendation, what is the impact?
>Is the fabric behavior different for M1/F1/F2 generation line cards?

The key is that Fab 2 in the chassis does not change the b/w 
capabilities of modules with a local fab 1. M1 10G cards are still 
80G/slot, F1 10G cards are still 230G/slot (with 5 fabrics).

>I understand the implications of over-subscription. If a 2x FAB-2
>chassis is not over-subscribed due to the mix of 1G and 10G ports,
>will the fabric perform correctly? (I'm thinking yes, as this is a
>simple math equation. There is no other fabric-magic going on.

Yes, you are correct - every card works and any port can talk to any 
port in the system even with a *single* fabric module. You 
(obviously) just won't get full bandwidth.

Hope that helps,

>Sales-Engineering is trying to convince me otherwise :-)
>Thanks for humoring me.
>cisco-nsp mailing list  cisco-nsp at puck.nether.net
>archive at 

Tim Stevenson, tstevens at cisco.com
Routing & Switching CCIE #5561
Distinguished Technical Marketing Engineer, Cisco Nexus 7000
Cisco - http://www.cisco.com
IP Phone: 408-526-6759
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