Specifications

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The PFC3C and PFC3CXL add the following features over the PFC3A/B/BXL
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Ingress and egress policers can operate independently of each other (in serial mode)
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Ingress IP DSCP and MPLS EXP marking at the IP-to-MPLS edge.
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Concurrent CoS and DSCP transparency for Layer 2 VPNs.
All versions of the PFC support the processing of QoS in hardware. This means that forwarding rates are not
impacted when QoS is enabled in the switch. The PFC3A/B/BXL can support centralised forwarding rates up to
30Mpps and the PFC3C/CXL up to 80Mpps
3.2 Distributed Forwarding Card (DFC)
The Catalyst 6500 architecture supports the use of Distributed Forwarding Cards (DFC). A DFC is used to hold a
local copy of the forwarding tables along with Security and QoS policies to facilitate local switching on the linecard.
The DFC3A is available as an option on CEF256 and CEF720 based linecards. The DFC3B and DFC3BXL were
introduced for linecards to operate with the Supervisor 720 equipped with PFC3B and PFC3BXL. The last generation
of DFC, the DFC3C, is available as an option on the CEF720 based linecards but are integrated on the latest
generation linecards, the WS-X6708 and WS-X6716.
Figure 4. DFC3C and the DFC3A
It is important to note that there are some operational considerations that can impact the ability of the Catalyst 6500
system to provide specific QoS features. This can happen when you mix different generations of PFC’s and DFC’s
together. The rule is that the system will operate at the lowest common feature denominator. The table below sets
out the operational level of the system based on a mix of DFC and PFC interaction.
Table 1. PFC/DFC Interaction Matrix
PFC3A PFC3B PFC3BXL PFC3C PFC3CXL
DFC3A Normal Operation PFC3B operates as a
PFC3A
PFC3BXL operates as
a PFC3A
PFC3C operates as a
PFC3A
PFC3CXL operates as
a PFC3A
DFC3B DFC3B operates as a
DFC3A
Normal Operation PFC3BXL operates as
a PFC3B
PFC3C operates as a
PFC3A
PFC3CXL operates as
a PFC3B
DFC3BXL DFC3BXL operates as
a DFC3A
DFC3BXL operates as
a DFC3B
Normal Operation PFC3C operates as a
PFC3BXL
PFC3CXL operates as
a PFC3BXL
DFC3C DFC3C operates as a
DFC3A
DFC3C operates as a
DFC3B
DFC3C operates as a
DFC3B and PFC3BXL
operates as a PFC3B
Normal Operation PFC3CXL operates as
a PFC3C
DFC3CXL DFC3CXL operates as
a DFC3A
DFC3CXL operates as
a DFC3B
DFC3CXL operates as
a DFC3BXL
DFC3CXL operates as
a DFC3C
Normal Operation
All DFC options allow fabric (crossbar connected) line cards to perform local switching. In order facilitate local
switching, QoS policies initially programmed into the PFC are pushed down and stored on the DFC3x. This process
negates the need to access QoS policies on the PFC when a local switching operation is in progress. Storing the
QoS policies on the DFC allows maximum local switching performance speeds to be maintained. The administrator