North American Network Operators Group

Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical

RE: CEF Load balancing...

  • From: Martin, Christian
  • Date: Mon Jan 17 10:59:35 2000

>We have a situation where CEF in a particilar 12.0.x version 
>broke the BVI
>interface in an IRB configuration w/ATM.   Then the next version broke
>forwarding between an ATM interface and a Ethernet interface in an
>interesting way (I haven't tracked down the specifics on the 
>second case

I've seen issues where CEF drives the CPU through the roof if it is doing
per-packet balancing on interfaces that reside on different VIPs.  I've also
seen links drop out of a CEF load-balancing group and the Adj Table hashes
not purge the down interface, or keep the hash indices the same, with only
two interfaces instead of three, thereby doing 67/33 balancing instead of
50/50.  The workaround is to diable and reenable CEF.

On the positive side, you can easily aggregate 200+Mbps across 6 DS3s with
minimal CPU and smooth, per-packet balancing.  Process switching on steroids
it is...  Besides, to uses reverse-path filtering, dCAR, dWRED, etc, you
need dCEF.

It is stable in 11.1.26CC1 - we use it all over for load-balancing on


>All in all, CEF works wonders, if it doesn't break something with its
>extra-fancy forwarding.
>- Forrest W. Christian ([email protected]) KD7EHZ
>iMach, Ltd., P.O. Box 5749, Helena, MT 59604
>Solutions for your high-tech problems.                  (406)-442-6648