cef/fast-switching question

Answered Question
Apr 11th, 2008
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I am a little confused. Seems by default most interfaces on a router are set for fast switching. What is the difference between cef and fast switching.


What do the following commands do:


ip route-cache cef

ip route-cache


Why would you not want cef/fast-switching?

Correct Answer by paolo bevilacqua about 9 years 2 months ago

In short, route-cache keeps a traffic-drive cache of most used destinations, that is aged periodically and doesn't really take much memory. CEF instead builds a table for all the destinations using prefix-based algorithm (Patricia trees) that you can search about.


The reason you disable that, is because certain features (less and less, but still there are some) don't work unless you do that and fail silently.


Hope this helps, please rate post if it does!


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Correct Answer
paolo bevilacqua Fri, 04/11/2008 - 21:12
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In short, route-cache keeps a traffic-drive cache of most used destinations, that is aged periodically and doesn't really take much memory. CEF instead builds a table for all the destinations using prefix-based algorithm (Patricia trees) that you can search about.


The reason you disable that, is because certain features (less and less, but still there are some) don't work unless you do that and fail silently.


Hope this helps, please rate post if it does!


boshardy1 Fri, 04/11/2008 - 21:14
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Is one of those cases to disable cef when you are doing vpn tunnels on a router?


I assume by your help earlier that cef is the way to go if it's a beefy router?

paolo bevilacqua Fri, 04/11/2008 - 21:30
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cef works in most cases of vpn/tunnels. If you want to see how much of you traffic is cef switch and how much is process, do "show interface switching".


A beefy router is needed every time traffic demands is enough. CEF is a must for any more than just moderate traffic.

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