[address-policy-wg] Source of routing table growth

Randy,

On Thu, 2011-06-30 at 08:45 +0900, Randy Bush wrote:
> > My understanding is that routing table growth is largely fueled by
> > traffic engineering rather than multihoming.
> 
> got cites?

As you know, I'm not a routing guy, so I tried to be careful with my
language here. I'm neither an operator nor a researcher, so if I sound
ignorant it is because I am. Having said that...

One simple way to look at it is to consider how much PI space there is,
versus routing table size. Looking at the latest copy of the RIPE
Database, we find just under 29k PI assignments. I am told that the RIPE
PI policy is the most lenient in the world, but if we assume that
similar policies are in place throughout the world that still leaves
less than 100k routes for all PI holders combined, compared to the 350k
routes total. This does not tell us anything about the *growth* exactly,
but it serves as a worst-case analysis: in the current Internet, most
routes come from non-PI allocations.


Further, a quick google for "routing table growth deaggregation" turns
up the following paper:

http://people.ee.ethz.ch/~wmuehlba/jsac-10.pdf

It is a couple years old, and I don't know if the authors are
trustworthy, but it seems nicely done. ;)

The authors were looking for trends in changes in traffic engineering
practices, and summarize:

        To sum up, given the differences in the two plots of Figure 7,
        we conclude that traffic engineering is a significant driver for
        address space deaggregation. However, based on the evolution
        since 2001, we cannot identify any sudden shift towards a more
        aggressive and widespread use of prefix deaggregation in order
        to achieve traffic engineering. This suggests that it is not an
        increasing demand for traffic engineering that inflates routing
        tables: rather, inflation is a consequence of the topological
        growth of the Internet combined with the lack of support for
        traffic engineering in the current routing system.

Nevertheless, if we look at Fig. 3., we see that the percentage of
prefixes from deaggregated routes has gone from like 17% in 2001 to 31%
in 2008 - almost double. So while the amount of routes due to traffic
engineering is not due to a fundamental change in practice, it seems
probable to me that it is nevertheless the source of a lot of routing
table growth.


Regarding the implications on policy... we seem to have a situation
where the people for and against increased IPv6 PI seem to think that
the other side must prove their position somehow. These ideas are all
based on potential future impact, and historically predictions about the
future have been very difficult.

Since we are talking about theories about future impact, we're kind of
like economists: the only real way to test a theory is to implement it
and see what happens. I will note that *not* changing the policy is also
implementing a policy, so no matter what we do, we're running an
experiment based on half-baked theories of how the Internet works. More
research will certainly inform the discussion and possibly lead to
better policies, but policies will never be based on perfect
understanding.

--
Shane