i am currently learning about CEF and i came across the command "no ip route-cache cef", which i do understand what it does, essentially, it enables Fast-switching/process switching on an interface.

What i don't seem to understand is to why would someone disable cef on an interface.

Could a wise networker provide me with a use case of disabling CEF on an interface?


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    Short version: don’t turn it off. Back in the early 2000’s there were occasionally CEF bugs where turning it off was a workaround (at substantial performance penalty). But in a high performance environment that was dangerous. On today’s modern silicon-forwarding routers turning it off is often not possible. Certain topologies automatically turned it off: on the old 7200 router routing between 802.1q (or was it ISL?) subinterfaces (router on a stick) automatically turned off CEF. In that case I switched routers to prevent the inevitable meltdown. – Darrell Root Feb 14 at 14:43
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    "Could a wise networker provide me with a use case of disabling CEF on an interface?" A wise network engineer does not disable CEF. – Ron Maupin Feb 15 at 1:44
  • In the early days of CEF it could not do per packet load balancing so if that was required you needed to switch to another switching method as well as all the BUGs as mentioned by Darrell – Matt Douhan Feb 17 at 21:10

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