From: Dennis J. Hartmann (dennisjhartmann@hotmail.com)
Date: Thu Apr 28 2005 - 00:57:54 GMT-3
All traffic sourced or destined to the router being evaluated is
process switched regardless of turning on CEF. You want to turn CEF off
when you're trying to evaluate traffic transiting a router with a debug.
As far as load-balancing is concerned, CEF offers the best
load-balancing features there are. Fast-switching was destination-based
only. CEF offered source-destination load-balancing in addition to
per-packet load-balancing. Process switching is ALWAYS per-packet
load-balanced. CEF by default does per source-destination because it works
much better for real time protocols (voice and video), as well as with old
TCP/IP stacks that don't re-order packets well.
Newer IOS versions offer more load-balancing varieties than simple
per source/destination and per-packet, but I forget what they are. Ar
Global Knowledge we teach the QoS class using 12.3(11T) and I've noticed
that the cef options for load-balancing have changed.
CEF is also the default in this IOS version!!!!! Oh yeah..... WFQ
is no longer the default on interfaces below E1 speeds. The default is
FIFO!
Sincerely,
Dennis Hartmann
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Brant I. Stevens
Sent: Monday, April 18, 2005 10:13 PM
To: Richard Gallagher; Mark Lasarko
Cc: ccielab@groupstudy.com
Subject: Re: ip cef?
You might want to disable CEF when issuing debugs, and you want traffic to
be process-switched.
On 04/18/2005 08:28 PM, "Richard Gallagher" <rgallagh@cisco.com> wrote:
> Mark,
>
> There are no real reasons that you want to disable CEF unless you were
> running into a bug where's it causing problems.
>
> You might find the following doc intersting, it answers some of your
> questions:
>
> -
> http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgc
> r/fswtch
> _c/swprt1/xcfcef.htm
>
> HTH, Rich
>
> --
>
> * Rich Gallagher - Cisco Systems TAC
> * CCIE #7211 - R&S, C&S
>
> Mark Lasarko wrote:
>
>> Just thinking - as much real world as the lab I suppose...
>> Are there *any* situations where 'ip cef' would not be desirable?
>> (aside from the obvious "do not issue the command ip cef")
>>
>> I can only think of two myself... and I am not sure if both apply??
>>
>> The first is proxy-arp, 'cause this can cause a routing loop
>>
>> The second is if you wanted to load-balance by the routing protocol
>> then you would not want cef The logic being that cef would assume the
>> load balancing functions over the routing protocol once populated.
>>
>> and while I have the burning smell inside my brain...
>> I recall reading that arp populates cef.
>> I also recall reading that when arp times out cef entries will do the
>> same are these two perceptions correct?
>> and with cef enabled (and populated) how does this impact arp
>> activity
>> - if at all?
>>
>> Thoughts?
>> ~M
>>
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