In this context, I think you might be interested in a measurement study that will be presented at INFOCOM this coming week. The focus of the study is BGP scalability with respect to churn rates. We have analyzed six years of Routeviews BGP update traces from four monitors in different tier-1 networks.

Some of the main findings are that
- BGP churn varies widely on many time scales, and cannot be understood through "black-box" statistical analysis. - The most severe churn experienced by these monitors are caused by mis-configurations and events that are local to the monitored AS. - Surprisingly, as much as 40% of churn consists of duplicate announcements, which are unnecessary for correct protocol operation. This figure has been pretty constant over our measurement period. - After filtering out duplicates, local effects and anomalies caused by a few specific events, we find that there is an increasing trend in "baseline" churn over the past six years, but that this growth is quite modest, and much slower than the growth in the DFZ RIB size.

The paper can be found at
Comments are always welcome.



Amund Kvalbein, Post Doc
Simula Research Laboratory

On 14. mars 2010 18:30, Paul Jakma wrote:
On Sat, 13 Mar 2010, Robin Whittle wrote:

Geoff's research is:

In the "Re: [rrg] draft-narten-radir-problem-statement-05.txt" thread

and in "BGP in 2009":

Those are the ones. I'd read that email too, but had forgotten of its
existence in replying to this thread - thanks for highlighting it.

It's possible that the current architecture of the internet is
holding back growth that should otherwise be there.

Yes. If we concentrate only on non-mobile networks, there are two
broad aspects of the routing scaling problem:

1 - The unreasonable, arguably unscalable, burden placed on the
DFZ routers individually, and on the DFZ control plane in
general, by the set of end-user networks which currently
get portability, multihoming and inbound TE by the only
means available: getting their own space and advertising it
as PI prefixes in the DFZ.

Well, why is it "unreasonable" exactly? If the system works and is
scalable, what's the problem?

It's only unreasonable if there's a /good/ way to keep those prefixes
out of the DFZ (i.e. good in the sense that it's at least as good as
what we have today). If such a way exists, then that's great - we should
definitely research ways to improve routing, of course.

However, it does not seem justified to say the current routing
architecture has a scaling problem. So it would not be justified, at
thhis time (AFAICT), to excuse inefficiencies added by proposed changes
on the basis that there's a pressing problem with the current architecture.

2 - The much larger number of end-user networks which could use 2
or more ISPs and which want or need portability, multihoming or
inbound TE but don't have it because they are unable to get the
space and advertise it. (Perhaps a subset of these could do
it, but don't because they known how unscalable it is.)

The growth in BGP advertised PI prefixes is the simplest measure of
the first aspect - which is like the tip of the iceberg. The less
visible part is point 2, like the main body of the iceberg.

Well, the internet is going to grow. That's hardly a surprise. What's
the problem with the internet growing? Geoff's results seem to show that
the growth is well within the scaling abilities of the 'net.

So even if Moore's Law keeps up in some acceptable manner with the
pace of growth in the number of PI prefixes in the DFZ, this doesn't
help with point 2 or with mobility.

Sure, but:

a) If the scope of the problem suddenly is "those very small
networks which want portability/multi-homing but aren't big enough
to get an AS and PI", then:

- it's a much, much smaller problem in terms of affected parties
than "internet routing doesn't scale"

- it's not clear even that such networks exist to any
meaningful extent (OK, I'm geeky enough that I'd love portability
and multihoming for my home network), i.e. if this is the
problem being solved then that changes the economic incentives
of roll-out.

b) If the problem is that fewer networks today can get PI, then we
should be able to see a change in the mode of prefix growth in the
historical data. However, TTBOMLK, we don't see this in the data.

Basically, if there's a problem then where is the evidence of it, now
that we seem to have initial evidence to suggest otherwise?

Sorry I haven't had time to revisit our discussions in early February.
I have a backlog of RRG messages to read and respond to - mainly
discussion following from my critiques of several architectures - and
I need to give priority to paying work.

No worries, that was just speculation on my part anyway. :)

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