[c-nsp] WS-X6716-10G local switching and etherchanneling

Tim Stevenson tstevens at cisco.com
Thu Jul 2 23:19:50 EDT 2009


Sam, please see inline below:

At 04:38 AM 7/2/2009, Sam Stickland contended:

>Hi,
>
>I've read:
><http://www.cisco.com/en/US/prod/collateral/switches/ps5718/ps708/prod_white_paper0900aecd80673385.html>http://www.cisco.com/en/US/prod/collateral/switches/ps5718/ps708/prod_white_paper0900aecd80673385.html
>
>If I'm understanding this correctly,

I don't see any mention of 6716 in this white paper. 6716 does not 
share the same architecture as any other 10G cards (eg 6708) 
mentioned there. 6716 is actually more like a 6704 front ended by 4:1 
muxes (at a high level - in reality, different chips are being used, 
ie, metro & r2d2 et al, not janus & rohini).

>communication between each bank of
>8 ports on a 6716-10G will be line-rate, but communication between the
>first and second groups of 8 ports will need to traverse the switch fabric?

While it's correct that ports 1-8 & 9-16 are on separate fabric 
channels, the key in the 6716 is that there is built-in *port-based* 
4:1 oversubscription.

In other words, 4 physical 10G ports feed into a single 10G chip 
(there are 4 such 10G chips on the card), ie, 4 ports share 10G of 
bandwidth at the port level.

So the maximum local switching performance you'd see in one half of 
the card is 20G, the same as you'd get into the fabric.

>On a similar note, if I create an etherchannel between two 6716-10G's
>will a module favour forwarding out of it's locally attached channel member?

No, it's just a hash decision - luck of the draw. Eg, packet comes in 
on t1/1 and channel member ports are t1/5 and t2/5. You've basically 
got a 50/50 chance that you'd pass over the fabric.

HTH,
Tim



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