[46659] in North American Network Operators' Group
Re: Load balancing in routers
daemon@ATHENA.MIT.EDU (Lincoln Dale)
Mon Apr 8 05:01:37 2002
Message-Id: <5.1.0.14.2.20020408015457.036319f8@203.9.111.130>
Date: Mon, 08 Apr 2002 02:00:32 -0700
To: Iljitsch van Beijnum <iljitsch@muada.com>
From: Lincoln Dale <ltd@interlink.com.au>
Cc: Richard A Steenbergen <ras@e-gerbil.net>,
abhijit bare <abhi1999us@yahoo.com>, <nanog@merit.edu>
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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.
