[c-nsp] do i *need* DFCs on the 6500?

[Ben Steele]

Unless you are hitting a cam limit on any of your resources on your SUP(very
possible if you are exporting netflow) OR you are congesting the crossbar
fabric(sh fabric util) which is pretty unlikely when you are talking a 24G
linecard on a 40G fabric connection then you probably won't see any
difference putting a DFC on a 6724

Remember these chassis are a hardware only based forwarding solution, so all
your doing with a DFC is moving cam/asic resources off the sup, so in
regards to your specific questions unless you have filled all your QoS
queues on the sup you are going to see nothing more on the DFC, also the sup
does (from memory) up to 100-200m pps in ipv6, I don't believe for a moment
you are even remotely close to this, and the global ipv6 routing table is no
where near the cam limit for that either, by the way is your SUP an XL? does
the DFC's on the 10G's match the sup or have they fallen back to the lowest
common configuration?

"...or could it be that DFC's are only really useful to a particular
deployment
and I just *think* i need them?  ;-)" - I think you might be on the money
here.

If you give us the current utilization of your cam resources(from the sup)
and the 6724 linecard throughput and what its functions
are(netflow/qos/mac/acls etc) then we can tell you for sure.

Ben


On Wed, Sep 2, 2009 at 9:16 PM, Alan Buxey <A.L.M.Buxey at lboro.ac.uk> wrote:

> hi,
>
> okay, from the background of I know what the DFC is and how it
> operates etc... i know I want them - however, I need to justify
> the upgrade/part cost to sort out a couple of 6500's.  in some of
> our 6500's, the 10G blades have DFCs already...but several 6724's dont
> (they just have CFC). ...as i said, I want them, but need to get
> some management/funding buy-in - and they dont want the 'what it
> does' information - they want some hard and fast facts that Cisco dont
> sem to want to tell me ..... so, the question is
>
> 1) is there any way of showing the sup720 strain/utilisation...particularly
> is there a way of showing DFC usage on the blades where we have them?
>
> 2) it offloads IPv6 and QoS - we're into both of those (and more so over
> the
> next year) - any particular insights into QoS performance/issues without
> DFC ? any throughput figures for IPv6 ?
>
> (i know that with CFC we're limited to the backplane (32mpps?) and we get ~
> 48mpps
> per blade with DFC)
>
> ...or could it be that DFC's are only really useful to a particular
> deployment
> and I just *think* i need them?  ;-)
>
> alan
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