Msfc, pfc and dfc roles in catalyst 6500 series switch
Multilayer Switch Feature Card (MSFC)
Multilayer Switch Feature Card is the Layer 3 switching engine that sites on the
Catalyst Supervisor as a daughter card. The MSFC is an integral part of the Supervisor
Engine, providing high performance, multilayer switching and routing intelligence. On
the MSFC daughter card, the route processor (RP) is located on the MSFC itself.
Equipped with a high performance processor, the MSFC runs layer 2 protocols on one
CPU and layer 3 protocols on the second CPU. These include routing protocol support,
layer 2 protocols (Spanning Tree Protocol and VLAN Trunking Protocol for example),
and security services.
The control plane functions in the Cisco Catalyst 6500 are processed by the MSFC
and include handling Layer 3 routing protocols, maintaining the routing table, some
access control, flow initiation, and other services not found in hardware.
Performance of the control plane is dependent on the type and number of processes
running on the MSFC. The MSFC3 can support forwarding rates up to 500Kpps. The
MSFC provide a means to perform Multilayer Switching (MLS) and interVLAN routing.
The MSFC builds the Cisco Express Forwarding information Base (FIB) table in
software and then downloads this table to the hardware
Application-specific-integrated circuits (ASICs) on the PFC and DFC (if present) that
make the forwarding decisions for IP unicast and multicast traffic.
Role of MSFC
1. Provide IOS based multi-protocol routing using a variety of routing protocols.
2. Work with the PFC for implementing layer 3 switching & traditional router
based input/output ACL's. Note, PFC can implement ACL's without requiring a
3. Provide other SW based features (like NAT, Policy Routing, Encryption etc.)
which are not supported in PFC hardware.
Table1. MSFC/Supervisor Compatibility Chart
MSFC Model Supervisor Model
MSFC1 Supervisor 1 or Supervisor 1A
MSFC2 Supervisor 1A or Supervisor 2
MSFC3 Supervisor 720 Models
MSFC4 Supervisor 720-10GE Models
Policy Feature Card (PFC)
The PFC3 is the ASIC-based forwarding engine daughter card for the Sup720; the
DFC3 is the ASIC-based forwarding engine daughter card for various fabric-enabled
line cards (CEF256, CEF720). Contains the ASICs that are used to accelerate Layer 2
and Layer 3 switching, store and process QoS and security ACLs, and maintain
The PFC3/DFC3 generation is built upon a forwarding architecture known as EARL7.
Within this generation, there are three different versions - 'A', 'B', and 'BXL' - that are
all based on the same fundamental technologies but that each have incremental
functionality. 'A' is the standard offering; 'B' is the intermediate option, and 'BXL' is
the high-end option.
The PFC contains a Layer 2 and a Layer 3 forwarding engine.
Role of PFC Layer 2 engine
1. Layer 2 MAC address lookups into the Layer 2 CAM table.
2. Looking into the packet headers to determine if this switching operation will
be a Layer 2 or a Layer 3 operation. If it is going to be a Layer 3 operation,
then it will hand off the packet to the Layer 3 engine for further processing.
Role of PFC Layer 3 Engine
1. NetFlow Statistics collection.
2. Hardware based forwarding of IPv4, IPv6 and MPLS tagged packets.
3. QoS mechanism for ACL classification, marking of packets, and policing (rate
4. Security mechanism for validating ACL rules against incoming packets.
5. Maintaining Adjacency entries and statistics.
6. Maintaining Security ACL counters.
The PFC3 supports hardware based Layer 2 and Layer 3 switching, processing
security and QoS ACLs in hardware and the collection of NetFlow statistics.
There are five versions of the Policy Feature Card in use today. The PFC3A , PFC3B,
and PFC3BXL are integrated into the Supervisor 720-3A, Supervisor 720-3B and
Supervisor 720-3BXL respectively. The PFC3B is the only option for the Supervisor 32,
while the PFC3C and PFC3CXL are integrated into the Supervisor 720-10G-3C and
Table2. PFC/Supervisor Compatibility Chart
PFC Model Supervisor Model
PFC1 Supervisor 1 or Supervisor 1A
PFC2 Supervisor 2
PFC3A Supervisor 720
PFC3B Supervisor 720-3B
PFC3BXL Supervisor 720-3BXL
PFC3C Supervisor 720-10GE-3C
PFC3CXL Supervisor 720-10GE-3CXL
Distributed Forwarding Card (DFC)
The Catalyst 6500 architecture supports the use of Distributed Forwarding Cards
(DFC). Distributed Forwarding Card is a combo daughter card comprising a MSFC and
PFC used by a fabric enabled Cat6500 linecard to perform distributed switching. DFCs
are located in linecards, not in Supervisors.
A DFC is used to hold a local copy of the forwarding tables (constructed by the MSFC)
along with Security and QoS policies to facilitate local switching on the line card. The
DFC3A is available as an option on CEF256 and CEF720 based line cards. The DFC3B
and DFC3BXL were introduced for line cards 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 line cards but are integrated on the latest
generation line cards, the WS-X6708 and WS-X6716.
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.
Table3. DFC/PFC Operation
PFC3A PFC3B PFC3BXL PFC3C PFC3CXL
operates as a
operates as a
operates as a
operates as a
operates as a
The primary MSFC3 will calculate, then push down a FIB table (Forwarding
Information Base) giving the DFC3x its layer 3 forwarding tables. The MSFC3 will also
push down a copy of the QoS policies so that they are also local to the line card.
Subsequent to this, local switching decisions can reference the local copy of any QoS
policies providing hardware QoS processing speeds and yielding higher levels of
performance though distributed switching.
Benefits of DFC
Performance is the biggest and most obvious reason to implement DFCs. You move
from a 30 Mpps centralized forwarding system anywhere up to a 400 Mpps
distributed forwarding system. This forwarding performance is for all L2 bridging, L3
routing, ACLs, QoS, and Netflow features, i.e., not just L3.
The performance benefit of a DFC is most applicable when you use the 67xx series
modules. This is because these modules have enough ports and bandwidth to
generate much more than the 30Mpps centralized forwarding engine has available. A
67xx-series module without a DFC is subject to the same centralized performance
characteristics of all other centralized forwarding modules.
DFC also minimize the impact that a classic module has in a system. Classic modules
do affect the centralized forwarding performance of a system, limiting the maximum
centralized forwarding rate to 15Mpps. Modules enabled with DFCs have their own
forwarding engine and are not subject to this performance degradation. If a classic
module used, the inclusion of a DFC mitigates any performance issues/concerns. Any
non-DFC modules are still subject to the available 15 Mpps of forwarding available
when a classic-module is present.
Packet Forwarding is done on the ingress forwarding engine. Therefore, packets
coming into the ports on the Sup720-3B will have forwarding done on the PFC3B of
the Supervisor. Packets coming into ports of line cards with DFC3s will have the
forwarding done on the DFC3. Packets coming into ports of line cards with CFCs will
have the forwarding done on the PFC3B of the Supervisor. The MSFC3 only does
forwarding in the cases where the PFC3 or DFC3 cannot make the forwarding
decision. Some of these cases include when traffic has IP Options set, when ACLs are
applied to an interface but the ACL is not programmed into the ACL TCAM for some
reason, when packets have TTL expiration, when packets hit an ACE with the "log"
keyword, and others.
Centralized Forwarding Card (CFC)
CFC is a centralized forwarding card for the switching modules which makes IPv4
Routing over the PFC. CFC does not do local forwarding, the forwarding is done by
the PFC in the Supervisor. As the forwarding is centralized, the PFC performance, FIB
entries, ACL lables are shared among the line cards that uses the Supervisor PFC for
forwrding. WS-F6700-CFC is the CFC card used on WS-X67xx Ethernet Modules. This
daughter card is supported only by the Supervisor Engine 720.
Note: CFC or the Centralized Forwarding Card was introduced along with the CEF720
modules. It provides centralized connectivity to the supervisor for look-ups and results.
Though the switch fabric is used for the data, but the CFC is responsible to send a
look-up request from the Supervisor and then get those results back.
Table4. CFC And Supported Modules
Cisco Catalyst 6500 Architecture White Paper
Catalyst 6500 Series Switch PFC,DFC and CFC FAQ
FAQ - Catalyst 6500 Hardware
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