Re: dual router vs. single "reliable" router

[David Barak <thegameiam () yahoo com>]

--- 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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