[c-nsp] Using DFC cards on a L2 6500/7600 system

[Tassos Chatzithomaoglou]

Watching the latest emails about DFC cards, i was wondering if the addition of WS-F6700-DFC3BXL cards to WS-X67xx modules would 
help a 6500/7600 in nay case, when used exclusively as a L2 switch (plus 802.1q tunneling/QoS/ACLs).


According to CCO:

The Cisco? Catalyst? 6500 Series Distributed Forwarding Card 3 (DFC3), including WS-F6700-DFC3A (DFC3A), WS-F6700-DFC3B (DFC3B), 
WS-F6700-DFC3BXL (DFC3BXL), is an optional daughter card for CEF720-based line cards such as WS-X6704-10GE, WS-X6724-SFP, 
WS-X6748-SFP, and WS-X6748-GE-TX. The DFC3 provides localized forwarding decisions for each line card and scales the aggregate 
system performance to reach up to 400 mpps. The new DFC3B and DFC3BXL offer enhancements to support Multiprotocol Label Switching 
(MPLS) and Access Control Entries (ACE) counters on the Cisco 6700 Series line cards. The DFC3BXL also has improved scalability to 
support one million IPv4 routes and 256-KB NetFlow entries.


Does the 400 mpps forwarding performance have any relationship with L2 switching?
Can you enable and use netflow on a L2 switch?

Something i could think of is probably "better" QoS characteristics.

6509#sh int gi1/1 capabilities | inc Model|QOS
   Model:                 WS-X6724-SFP
   QOS scheduling:        rx-(1q8t), tx-(1p3q8t)		<- CFC

6509#sh int gi8/1 capabilities | inc Model|QOS
   Model:                 WS-X6724-SFP
   QOS scheduling:        rx-(2q8t), tx-(1p3q8t)		<- DFC3BXL


Also when using non-fabric & fabric modules (yep, i know that's a no), the fabric ones with DFCs use "dCEF/flow through" as a 
Switching Mode, while the fabric ones without DFCs use "Crossbar/CEF/truncated". Is there any advantage of this on L2 switching?

6509#sh platform hardware capacity system
System Resources
   PFC operating mode: PFC3BXL
   Supervisor redundancy mode: administratively sso, operationally sso
   Switching resources: Module   Part number               Series      CEF mode
                        1        WS-X6724-SFP              CEF720           CEF
                        2        WS-X6724-SFP              CEF720           CEF
                        6        WS-SUP720-3BXL        supervisor           CEF
                        8        WS-X6724-SFP              CEF720          dCEF
                        9        WS-X6408A-GBIC           classic           CEF

6509#sh fabric switching-mode
Global switching mode is Truncated
dCEF mode is not enforced for system to operate
Fabric module is not  required for system to operate
Modules are allowed to operate in bus mode
Truncated mode is allowed, due to presence of DFC, CEF720 module

Module Slot     Switching Mode
     1                 Crossbar
     2                 Crossbar
     6                      Bus
     8                     dCEF
     9                      Bus


6509#sh platform hardware capacity fabric
Switch Fabric Resources
   Bus utilization: current: 0%, peak was 67% at 15:39:57 EET Thu Feb 15 2007
   Fabric utilization:     Ingress                    Egress
     Module  Chanl  Speed  rate  peak                 rate  peak
     1       0        20G    0%    1% @09:35 15Feb07    1%   26% @16:36 15Feb07
     2       0        20G    1%    3% @23:13 13Jun07    1%    1% @15:40 24May07
     6       0        20G    0%   11% @06:41 30Mar07    0%   26% @16:36 15Feb07
     8       0        20G    0%   26% @16:36 15Feb07    0%   11% @06:41 30Mar07
   Switching mode: Module                                        Switching mode
                   1                                                  truncated
                   2                                                  truncated
                   6                                               flow through
                   8                                                    compact



Is there something else i'm missing?


-- 
Tassos