dCEF

[littlegrave]

Hello everyone,

I'm currently trying to understand the concept of dCEF and how it works. I have a pretty straightforward question. I would like to know if when using dCEF the FIB is distributed equally among all Layer 3 forwarding engines so that each of them has the same FIB or the FIB is spread amongst all of them as each of them contains just a part of the whole FIB. I hope someone can give me an explantion about it since it's a bit unclear in the Cisco Press book I am currently reading. Thank you

[glen.grant]

Each dcef card has the complete FIB table I believe .

[sachinraja]

I think glen is right.. When dCEF is enabled, line cards maintain identical copies of the FIB and adjacency tables. The line cards can perform the express forwarding by themselves, relieving the main processor - Route Processor (RP) - of involvement in the switching operation.

Raj

[Amit Singh]

Hello,

dCef is distributed Cisco Express forwarding.dCEF is used in high-end switches and Cisco routers. On 6500/7600 for dCEF to work you need the DFC's (distributed feature card) which is actually a PFC which used on Supervisor engine. This DFC is a Layer2/3 packet rewrite engine and downloads the CEF FIB and Adjacenecy tables on itself. Once the line-card has CEF FIB and adjacency table downloaded from the RP it locally writes the packet and hence doesn local switching.

With dCEF enable cards even the first packet doesnot go to the CPU for processing unless the traditional MLS where the first packet goes to the CPU and then the subsequent packets are written locally.There are certain conditions if they donot meet then the packet goes to the CPU for processing like TTL expire,MTU exceded etc...

With DFC enabled on the 6500/7600 switches, the performance of the switch increases to 400+ MPPS.

HTH,Please rate if it does.

-amit singh

[littlegrave]

Thank everyone for the quick replies!