Re: Converged Networks Threat (Was: Level3 Outage)

[David Meyer <dmm () 1-4-5 net>]

        Petri,

> > I think it has been proven a few times that physical fate sharing is 
> > only a minor contributor to the total connectivity availability while 
> > system complexity mostly controlled by software written and operated by 
> > imperfect humans contribute a major share to end-to-end availability.

        Yes, and at the very least would seem to match our
        intuition and experience. 

> > From this, it can be deduced that reducing unneccessary system 
> > complexity and shortening the strings of pearls that make up the system 
> > contribute to better availablity and resiliency of the system. Diversity 
> > works both ways in this equation. It lessens the probablity of same 
> > failure hitting majority of your boxes but at the same time increases 
> > the knowledge needed to understand and maintain the whole system.

        No doubt. However, the problem is: What constitutes
        "unnecessary system complexity"? A designed system's
        robustness comes in part from its complexity. So its not
        that complexity is inherently bad; rather, it is just
        that you wind up with extreme sensitivity to outlying
        events which is exhibited by catastrophic cascading
        failures if you push a system's complexity past some
        point; these are the so-called "robust yet fragile"
        systems (think NE power outage).  

        BTW, the extreme sensitivity to outlying events/catastrophic
        cascading failures property is a signature of class of
        dynamic systems of which we believe the Internet is an
        example; unfortunately, the machinery we currently have
        (in dynamical systems theory) isn't yet mature enough to
        provide us with engineering rules.    

> > I would vote for the KISS principle if in doubt.

        Truly. See RFC 3439 and/or
        http://www.1-4-5.net/~dmm/complexity_and_the_internet. I
        also said a few words about this topic at NANOG26
        where we has a panel on this topic (my slides on 
        http://www.maoz.com/~dmm/NANOG26/complexity_panel).

        Dave