[c-nsp] egress replication capability on CFCs?

[Tim Stevenson]

Christian,

Strictly speaking, no, egress replication does NOT require DFC, it 
only requires a switch fabric & egress capable replication engines on 
the linecards (such as those on 67xx cards).

The auto-detection is based only on card type, not whether there is a 
DFC present. It could be argued either way which is the better mode 
for CFC equipped cards, ingress or egress.

With CFC, egress replication still gives you decreased fabric 
bandwidth consumption and distributed replication - but, at the same 
time, it could increase your system bus utilization, especially in a 
VLAN/SVI or distributed etherchannel environment, because you may do 
multiple lookups for the "same" OIF, one for each egress card with 
that OIF (eg, SVI 100 on cards 1 2 & 3 would each submit a lookup for 
the replicated copy to the PFC over the bus in egress mode; vs 
ingress mode where only one copy would be looked up at the PFC).

In the end, though, at realistic packet sizes & data rates, this is 
probably not a major consideration, but you should probably consider 
monitoring bus, fabric, and fwding engine utilization to make sure 
you're not on the hairy edge.

Thanks,
Tim

At 04:51 PM 10/9/2006 +0100, christian.macnevin at uk.bnpparibas.com commented:
>Hi,
>
>I was under the impression that egress multicast replication required an
>onboard DFC on a 67XX card, yet
>I've got a box fully populated with 6748-SFP cards here telling me it's
>current mode of replication is Egress.
>
>Doesn't this require the MET to be programmed onto the DFCs?
>
>Cheers
>Christian
>
>
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Tim Stevenson, tstevens at cisco.com
Routing & Switching CCIE #5561
Technical Marketing Engineer, Catalyst 6500
Cisco Systems, http://www.cisco.com
IP Phone: 408-526-6759
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