RE: CEF Load balancing...

["Martin, Christian" <CMartin () mercury balink com>]

> 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
> yet.)

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
DS3s...

Chris

> All in all, CEF works wonders, if it doesn't break something with its
> extra-fancy forwarding.
>
> - Forrest W. Christian (forrestc () imach com) KD7EHZ
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