Re: dual router vs. single "reliable" router

[Richard A Steenbergen <ras () e-gerbil net>]

On Thu, Apr 10, 2003 at 08:07:14AM -0700, David Barak wrote:
> There are many assumptions and statements about reliability, but the
> methodology of how the numbers were reached is not present.  If one
> assumes that one has a router which fails very rarely, this would
> dramatically affect network design.  However, this is an assumption, not
> a conclusion.  The assumption of the paper is that the Alcatel box has
> ultra-low failure rates, while the Juniper and Cisco boxen have
> relatively high failure rates.  Personally, before I let something like
> this influence my buying/design decisions, I'd want to see some serious
> raw data...

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.

Throw in some assumptions (which may or may not be true, I'll agree that
some of their numbers are a little "off") that every one of those failures
involves some service impact, you could easily make a case that one box 
which doesn't go down is better than two boxes which routinely go down.

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. :)

-- 
Richard A Steenbergen <ras () e-gerbil net>       http://www.e-gerbil.net/ras
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