[57445] in North American Network Operators' Group
Re: dual router vs. single "reliable" router
daemon@ATHENA.MIT.EDU (David Barak)
Thu Apr 10 12:08:17 2003
Date: Thu, 10 Apr 2003 09:07:37 -0700 (PDT)
From: David Barak <thegameiam@yahoo.com>
To: Richard A Steenbergen <ras@e-gerbil.net>
Cc: nanog@nanog.org
In-Reply-To: <20030410155400.GQ41027@overlord.e-gerbil.net>
Errors-To: owner-nanog-outgoing@merit.edu
--- Richard A Steenbergen <ras@e-gerbil.net> wrote:
> 2x the hardware means 2x the number of hardware
> failures. It also means 2x
> the number of software upgrades, and probably some
> multiplier greater than
> 2x for the increased complexity and opportunity for
> software to go wrong.
> Dual routers just increases the number of overall
> failures in exchange for
> hoping that only one goes down at any given time.
The fallacy here is that the greater number of
failures which a dual-router scenario will encounter
are of the same Qualitative type as the failures your
single router will encounter.
This is clearly not true: one of a pair failing means
that there will be a period of convergence, and then
the remaining router will carry the load. If a single
router fails, the load will not be carried until the
router can be restored.
> On one side of the coin, Cisco has done a masterful
> job at convincing the
> networking industry that the correct answer to their
> routine failures is
> to purchase double of everything. On the other
> side... Show me the box
> that never goes down. :)
My point exactly: from a design perspective it's much
simpler to have a single box, but I have not seen
single boxen which don't fail.
I'm actually a big fan of the "cold-spare" approach:
you preserve your simplicity, and any outage only
lasts as long as it takes to unplug and re-plug...
=====
David Barak
-fully RFC 1925 compliant-
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