It is fair to say that we need a new routing system

August 8th, 2007 by kc

i get this question a lot:

at the current churn rate/ratio, at what size does the
FIB need to be before it will not converge? (also sometimes pronounced ‘when will the current Internet routing architecture break?’)

a good question, has been asked many times, and afaik no one 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.
  2. there are economics and policy and social factors we can’t predict, e.g., how much convergence-capable hardware will providers/vendors be able to afford, how those costs will affect consumer prices, how that will affect consumer uptake, network growth, and industry dynamics, how regulation affects all of the above.
  3. we have no data from providers on the dynamics of BGP and IGP interactions, much less network wide convergence, so the research community can’t provide any empirically grounded input into an answer.

note, however, that like the ‘when do we run out of address space?’ question, uncertainties in both technology progress and human behavior render any prediction of an actual convergence apocalypse timestamp rather sketchy, and i reckon someone with an agenda could devise parameters and ‘observe correlations’ to match their agenda.

also note that this does not mean we don’t have a problem, just like not having a validated ipv4 address exhaustion timestamp means does not mean we don’t have a problem with address exhaustion.

the reason we know we have a problem, and that it’s only a matter of time before we’ll need another approach to routing, is that the current system is inherently not scalable indefinitely, and in particular is inherently a poor fit to the topology and traffic engineering practices that underlie the ‘natural’ operations and evolution of the infrastructure.

this is why the IAB still has workshops about the issue even though they don’t actually have any empirical data in the workshop report, and whenever the report touches on this question ‘how long do we have?’, they add “Editor’s note: This is an area of much controversy/debate, so further investigation/community input is required” (those type of words are in the report many times, sometimes before and after the same paragraph (see section 4 on the scaling problem.)):

with neither a ‘macroscopic data analysis’ directorate of the IETF (or IRTF) nor an industry structure that could give rise to such an activity, the IAB punts on the ‘supporting empirical data’ aspect of the issue, and instead focuses on what it can contribute: engineers discussing/ establishing/documenting what we do know about ‘fundamental problems w scalability and proposed engineering approaches to solving them’. if you were at the nov06 ietf plenary when the IAB presented this workshop summary, you may recall a few people in the audience got up and said ‘what data are you even basing this sky-is-falling stuff on?’ and the IAB again acknowledged the data gap, said “we’ll get back to you” and afaik at no point did they provide any data. (if they did please let me know, we’ll publish the numbers..)

we’re not alone in wanting better quantitative data on this topic, but such data is not essential to recognizing or understanding the problem. better data would assist those trying to get attention and resources invested in a better routing system, but that’s (we are) a small and highly unprofitable market segment for those who have the data. i’m not giving up on the data challenge, but, in the meantime, it is fair to say that we need a new routing system.


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