Load balancing in routers

Lincoln Dale ltd at interlink.com.au
Mon Apr 8 09:00:32 UTC 2002


At 10:50 AM 8/04/2002 +0200, Iljitsch van Beijnum wrote:
> > load balanced across those links. Some mechanisms (for example Cisco CEF)
> > can do this on a per-destination (flow-based) basis, to prevent packet
> > reordering.
>
>I seem to remember fast switching was per-destination, and CEF was
>round robin. But it seems CEF is now per-destination as well in IOS 12.2.
>Round robin is optional.

you remember incorrectly.

by default, CEF uses a hash based on both src & dst to determine the path 
to take.
somewhat
paradoxically this is referred to as "per-destination" load-balancing (or 
"deterministic").

on many platforms, you can reconfigure CEF to use a per-packet distribution.

"ip load-sharing XX" is the interface command to set the policy.

"per-destination" historically is what fast-switching used to do -- and it 
did a particularly bad job of handling large amounts of traffic sourced to 
one ip-address (such as a news-server or proxy-server).  this was 
particularly apparent for multiple <E1 links load-balanced using equal cost 
routes.


cheers,

lincoln.




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