Are there any circumstances where using CEF is NOT a good idea? For example, to my knowledge, using fast switching (ip route-cache) is not a good idea when using NAT. Maybe CEF also has some situations where it might conflict or break something. I am thinking of turning on CEF wholesale on all my routers but I don't want to break anything in the process.
For some features, eg QoS, CEF is required on the router. CEF is a faster fwd path so is preferred, however, you should understand the features you configure and any caveats related to them.
I don't know of any situations where CEF is bad--any features that aren't supported are automatically punted back to the process switching path.... Unless you are troublshooting a specific problem where cef is preventing you from seeing debugs, or unless you know of a specific bug in CEF that's going to cause you problems, I'd turn it on.
Russ.W
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