Re: Question on IP CEF

From: MADMAN (dave@interprise.com)
Date: Tue Jun 10 2003 - 12:46:08 GMT-3


Jonathan V Hays wrote:
> It would be nice to know, just for the sake of curiosity.
>
> But if most docs say to enable CEF with CAR, it's probably a good habit
> to have, especially for the CCIE lab where you might lose points without
> it.
>

   Well I did a quick test and CAR appeared to work when I disabled CEF
as well as when CEF was enabled. This was from a 7206VXR running
12.2.13. I set the parameters rediculously low so that the effects
would be obvious:

interface FastEthernet0/0
  ip address 172.28.64.9 255.255.255.0
  rate-limit output 8000 2000 4000 conform-action transmit exceed-action
drop
  load-interval 30
  duplex half
  speed 100
  no cdp enable

with CEF disabled:

C7206VXRB#sh interfaces rate-limit

FastEthernet0/0
   Output
     matches: all traffic
       params: 8000 bps, 2000 limit, 4000 extended limit
       conformed 1214 packets, 257621 bytes; action: transmit
       exceeded 216 packets, 172397 bytes; action: drop
       last packet: 0ms ago, current burst: 2057 bytes
       last cleared 00:08:34 ago, conformed 4000 bps, exceeded 2000 bps

   I was simply pinging from the router and with CAR I was loosing
roughly 50% of the packets whether or not CEF was enabled.

   To make sure it wasn't a fluke I adjusted the parameters and the
traffic was policed properly whether or not I had CEF enabled.

   Maybe someone from Cisco lurking may have a logical explanation;)

David Madland
CCIE# 2016
Sr. Network Engineer
Qwest Communications
612-664-3367

"Government can do something for the people only in proportion as it
can do something to the people." -- Thomas Jefferson



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