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CCNP Enterprise Core (350-401) Cisco Packet Forwarding

Hardware Cisco Express Forwarding (CEF)

ASICs in hardware platforms are expensive to design, produce and troubleshoot and limited in their functionality yet they allow for very high packet rates due to only being programmed for specific tasks.

By LiveWireInnovation – Own work, CC BY-SA 3.0

Routers can also be equipped with network processing units (NPUs). NPUs have an advantage over ASICs as they are programmable meaning their programming and firmware can be changed with ease.

Distributed forwarding architectures with hardware CEF allow packet throughput to be greatly increased by offloading packet switching responsibilities to one or more line cards. Packet switching accomplished in distributed platforms is done via dCEF (Distributed Cisco Express Forwarding). dCEF allows CEF data structures to be downloaded to ASICs and the CPUs of all line cards so they can all participate in packet switching. The main advantage of this is switching can be done at a distributed level and increasing the packet throughput of the router.

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