[nsp] Cisco 2500 Traffic Limit and high cpu utilization.

[Terry Baranski]

> Hi, 
> IOS version we are dealing is IOS version 12.1(20)
> Interfaces consist of ethernet, serial and 
> group async. A LAN and dialups took gateway as this
> router.  We have a large ACL on each interaface.
> It works fine. In busy times out load gets significantly 
> high. I tried to enable ip cef, but it didn't work it out.
> What could went wrong? I will appriciate for any comment
> or an idea.

As Justin mentioned, the CEF problems you had were probably the result
of bugs, as any traffic that can't be CEF switched for whatever reason
is normally just punted down to the next switching path (e.g., fast
switching) rather than dropped or anything of that nature.  So an IOS
upgrade may be in order.  

That being said, what is the bandwidth of the serial interface and
approximately how much traffic do you think is going through the router
when the CPU usage gets high?  And how high does the CPU usage get?  If
most of the current traffic is being fast switched (it should be;
confirm with "show interface switching"), CEF may not even make that big
of a difference. (You can't know for sure until you try it, but it would
be wise to keep in mind that CEF isn't a definite fix here.)  I
mentioned performance-reducing features earlier and you have a good
number of them enabled.  You may simply be approaching the limit of what
a 2500 can handle under such a configuration.

-Terry