Unanswered Question
Giuseppe Larosa Wed, 03/03/2010 - 02:01

Hello Alsayed,

PFC and DFC are specific HW components of C6500 architecture.

PFC is a necessary component and is physically a submodule of supervisor.

PFC with the help of MSFC routing engine prepares and keeps updated the master copy of CEF table used for multilayer switching.

DFCs are submodules that can be installed on recent linecards and allow the linecard to work in distributed CEF mode: the DFC keeps a copy of the whole CEF  table.

So PFC writes the master copy, DFCs get a fresh copy of the CEF table.

if a new packet enters a port in a linecard equipped with DFC, even the first packet can be switched without consulting the main cpu because DFC looks at CEF local copy to find out how to rewrite the frame that will contain the packet.

if the same linecard has a CFC instead of a DFC the linecard does not work in distributed mode.

see C6500 architecture white paper:


Hope to help


Jon Marshall Wed, 03/03/2010 - 02:59


Just as another perspective.

The PFC and DFCs are primarily used to forward traffic at both L2 and L3 in a 6500 switch. The MSFC on the other hand does not forward traffic but is reponsible for building the routing tables, establishing routing neighborships etc.

A DFC as explained is simply a local forwarding card, local as in the sense that it is on the actual linecard.

The PFC is also responsible for QOS/ACLs etc. ie. pretty much all functions carried out in hardware on the 6500.



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