Ben Steele wrote:
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
That depends completely on what other cards are on the box, what their
offered forwarding load is, and whether they have DFCs.
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
No. The PFC3 does 30Mpps IPv4 (and 15Mpps IPv6 I think). A DFC3 does
48Mpps IPv4 (and 24Mpps IPv6).
http://www.cisco.com/en/US/products/hw/switches/ps708/products_qanda_item09186a00809a7673.shtml
A fully-populated and fully-DFCed 6509 does 400Mpps IPv4 or 200Mpps IPv6
(well, actually 192Mpps - 24x8 linecards). In this configuration, the
PFC does very little.
It's worth noting that a 6724 doing 64-bytes packets on all ports offers
~47Mpps forwarding load - well in excess of the PFC capacity. A chassis
full of 6724s without DFCs at 10% load with 64-bytes packets also
exceeds the PFC capacity.
Obviously these are worst-case numbers but illustrative of the problems
you can get yourself into if you don't capacity plan well.
It's worth noting that some linecards have different (i.e. more
flexible) rx & tx queueing methods with a DFC versus the CFC.
There's also the bus-stall issues, which go away (supposedly) with a DFC
installed since they're not connected to the bus.
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?
I'm not sure why you mention CAM limits, but it's worth noting that DFCs
do not help with FIB CAM at all, since they hold a copy of the PFC FIB.
Personally we get DFCs on everything since we're using plain -3B (or -3C
not) rather than XL, and the cost of the DFC is a pretty minimal
percentage of the linecard for the future-proofing.
We've also seen software bugs manifest on CFC cards in the past; this
implies to me that Cisco "prefer" DFC chassis. Similarly some of the new
linecards e.g. 6708/6716 are DFC-only. I suspect that will be the case
going forward.
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