[c-nsp] WS-6748-SFP with or without DFC?

[Tim Stevenson]

Long explanations inline below:

At 10:08 AM 3/14/2006, christian.macnevin at uk.bnpparibas.com vociferated:

>Definitely useful, thanks.
>
>When you say 'efficient egress replication', it seems as though it 
>already does egress replication on the
>67 line cards, as the MET is distributed, no? If so, what's the difference?

If you are running w/egress replication, but do not have DFCs, then 
all the lookups are done on the PFC - the ingress lookup, the fabric 
packet lookup, and all the replication lookups as well. Whereas 
w/DFCs, the egress DFC does the lookup at the linecard level. So 
without DFCs, you are doing lookups over the bus, which will increase 
the latency, and also, if there are say 3 modules with receivers in 
VLAN 10, each will do its own replication for VLAN 10 & submit the 
packet for lookup at the PFC, vs ingress replication, where only 1 
packet is replicated & submitted for a lookup.

In a nutshell, it is perhaps questionable that we run in egress mode 
by default on CEF720 cards even if there are no DFCs, but that's the 
way it is implemented today. It is of course more efficient in terms 
of fabric utilization, but at the expense of increased bus 
utilization & increased PFC fwding engine lookups.


>With NF, does it record total multicast output to a group accurately 
>when you're doing egress replication? Or does that
>require the DFC?

So egress multicast accounting in egress replication mode is not 
supported today. You can see the NF records on the fwding engines but 
they are not exported. This will be supported in a future software 
release, with the caveat that with VLANs, you will get an egress 
record exported from any fwding engine with a receiver in that vlan 
(vs ingress replication mode, where you will only get one record per 
egress vlan).

Tim





>Internet
>tstevens at cisco.com
>
>13/03/2006 11:35
>To
>Christian MACNEVIN, cisco-nsp
>cc
>Subject
>Re: [c-nsp] WS-6748-SFP with or without DFC?
>
>
>
>
>DFC distributes *everything* from the PFC - L2, IP, MPLS, ACLs/QoS, &
>netflow. The PFC & DFC ASICs are the same.
>
>With respect to multicast, DFCs give you efficient egress multicast
>replication, saving fabric b/w, and increase the aggregate multicast
>lookup throughput for the system.
>
>With respect to NF, DFCs give you a dedicated NF table on each DFC +
>on the PFC - each fwding engine maintains its own NF table. So you
>can collect stats for many more flows than w/a centralized fwding
>engine system.
>
>Note that w/NFv9, we can now export IPv4 multicast flow data from
>6500, which may be of use to you based on the requirements you outlined.
>
>Tim
>
>At 05:22 PM 3/13/2006, christian.macnevin at uk.bnpparibas.com vociferated:
> >Hi,
> >
> >Just looking at one of Tim's presentations from Power sessions, and the
> >CEF720 module architecture.
> >What functionality does the DFC add/distribute on the 67XX cards? This is
> >relevant to a high-performance
> >multicast enabled LAN environment where we're starting to consider NetFlow
> >as a potentially major
> >source of information.
> >
> >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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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
********************************************************
The contents of this message may be *Cisco Confidential*
and are intended for the specified recipients only.