[nsp] ip cef

[Kinczli Zoltán]

Hello,

  Checking the 'sh ip cef not' output might be useful sometimes, watch for unsupp'ted column.
Not every feature is supported in CEF path (and, of couse, it depends on the ios version you are running
for instance, multilink-PPP, dot1q, just to mention two from the most frequent ones). So, if packet can not
be cef switched, it's punted back to next 'slower' path, that is fast switching.

regards
 --zoltan

-----Original Message-----
From: Oliver Boehmer (oboehmer) [mailto:oboehmer at cisco.com]
Sent: Monday, December 01, 2003 9:52 PM
To: James Galliford; Hugo
Cc: cisco-nsp at puck.nether.net
Subject: RE: [nsp] ip cef




> I believe that if the router does not have the route in its CEF table
> that it process switches the first stream and therefore you'll see the
> entry in the ip cache.  After the router knows the path and determines
> the optimum switching method, it will then create an entry in the CEF
> table for the path.  The path will then be invalidated from the route
> cache.
> 
> This is to the best of my understanding of course.

But this is wrong ;-), you are basically describing fast switching. CEF
is not a demand-based cache, it is populated from the routing table.
When we try to CEF-switch a packet and there is no FIB entry for the
destination, the packet is dropped.

Hugo: you're possibly seeing entries in the fast cache for packets
processed by the CPU, including packets generated by the router itself.
Newer IOS releases also use CEF in the process path..

	oli

> -----Original Message-----
> From: Hugo [mailto:netw2004 at hotmail.com]
> Sent: Monday, December 01, 2003 3:01 PM
> To: James Galliford
> Cc: cisco-nsp at puck.nether.net
> Subject: Re: [nsp] ip cef
> 
> 
> Hi James!!!
> 
>           You are right. Now I see less entries in the table, but I
> thought that all the packets would be cef switched. Why not? Thanks!!!
> 
> 
> ----- Original Message -----
> From: "James Galliford" <JamesG at corp.ptd.net>
> To: "Hugo" <netw2004 at hotmail.com>; <cisco-nsp at puck.nether.net>
> Sent: Monday, December 01, 2003 8:24 PM
> Subject: RE: [nsp] ip cef
> 
> 
> Hugo,
> 
> Whenever any packet is process switched you will see an addition to
> the # of adds in the ip cache output.
> 
> You are probably seeing a much lower # of entries in the route cache
> since turning on cef though correct?  If not, maybe CEF is not running
> on all interfaces?
> 
> Thanks.
> 
> -----Original Message-----
> From: Hugo [mailto:netw2004 at hotmail.com]
> Sent: Monday, December 01, 2003 12:43 PM
> To: cisco-nsp at puck.nether.net
> Subject: [nsp] ip cef
> 
> 
> Hi!!!
> 
> 
>              Just an easy question. I have just enabled Ip cef on my
> router, but I still see new entries in the cache table when I execute
> the "show ip cache" command. Could someone tell me if this is the
> right way of cef working? Thanks!!!
> 
> Regards
> 
> H
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