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Distributed CEF

Unanswered Question
Mar 27th, 2014
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Hi, I read some information about dCEF wherein a copy of the FIB will be pushed to the linecard to offload traffic from the RP. My question is, is this applicable to 6500 switches with cards that has DFCs? I have a 6500 switch with Sup720-3B, some linecards does not have DFC, some have CFC, and some have DFCs. Would it be better to turn on "ip cef distributed"? Is the performance going to improve? If I enable distributed CEF, is there going to be an impact or downtime? I know it is always advisable to do this during window time but we are running 24/7. Thanks in advance. JL
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Jon Marshall Thu, 03/27/2014 - 12:27
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Yes it is applicable to 6500 linecards with DFCs in them. The supervisor will download a copy of the FIB to the linecard so it can make local forwarding decisions without having to send a part of the packet to the supervisor.

On the 6500 "ip cef distributed" is enabled by default so you shouldn't need to turn anything on ie. if you have DFC linecards they should already be using a local FIB for switching decisions.


Joseph W. Doherty Thu, 03/27/2014 - 12:27
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Distributed CEF might be the default for 6500's DFCs.  (I recall back in the 7500 days, you needed to explictly enable it for VIP cards to run CEF too.)


Try show cef state, and see if you see dCEF enabled/running in the output.


If you have DFC, yes it's better for distributed CEF to be active.  Whether you would "see" a performance difference is a "it depends" answer.


I'm not positive, but I suspect enabling or disabling dCEF would cause no or minimal impact (minimal, as in, drop a few packets in transit).


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