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.
More information about the NANOG
mailing list