too many variables

Joel Jaeggli joelja at
Fri Aug 10 00:15:47 UTC 2007

Lincoln Dale wrote:
>>  I asked this question to a couple of folks:
>> 	"at the current churn rate/ration, at what size doe the FIB need to
>>          be before it will not converge?"
>>  and got these answers:
>> --------- jabber log ---------
>> a fine question, has been asked many times, and afaik noone has
>> provided any empirically grounded answer.
>> a few realities hinder our ability to answer this question.
>> (1) there are technology factors we can't predict, e.g.,
>>         moore's law effects on hardware development
> Moore's Law is only half of the equation. It is the part that deals with route
> churn & the rate at which those can be processed (both peer notification and
> control-plane programming data-plane in the form of FIB changes).

Moore's law just makes an observation that the transistor count feasible
for a minimum cost component doubles every 24 months. It actually says
nothing about the performance of those components or their speed.

> Moore's Law almost has zero relevance to FIB sizes. It doesn't map to growth in
> SRAM or innovations/mechanisms for how to reduce the requirements for SRAM
> while growing FIB sizes.

sram components are following their own trajectory and you can fairly
easily at this point project how big a cam you'll be able to buy and
what it's power consumption will be out a couple years from the products
currently in your routers (which are for the most part not state of the
art). That said, not all forwarding engines in line cards  utilize
ternary cams or srams so assumptions that involve sram and sram-like
components being the only game in town for fib storage are dangerous.

> cheers,
> lincoln.

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