Science vs. bullshit
Patrick W. Gilmore
patrick at ianai.net
Mon Oct 19 20:05:15 UTC 2009
Lightning talk followup because I want to make sure there was not a
miscommunication. A two sentence comment at the mic while 400+ of
your not-so-close friends are watching does not a rational discussion
The talk in question:
The disagreement is whether Renesys can reliably find out how many
transit providers an AS has. Remember, we are discussing transit
providers here, not peers.
My point is if an AS has _transit_, then it must be visible in the
global table (assuming a reasonably large set of vantage points), or
it would not be transit. Of course, this is not perfect, but it is a
pretty close approximation for fitting curves over 10s of 1000s of
ASes. So things like "I have two transit providers, and one buys
transit from the other" is a small number and not relevant to fitting
curves. (It also means you are an idiot, or in a corner of the
Internet where you should probably be considered as having only one
Majdi has pointed out other corner cases where transit is not viewable
through systems like Rensys. For instance, announcing prefixes to
Provider 2 with a community to local-pref the announcement below peer
routes. That means only one transit is visible in BGP data.
There were several reasons some of us did not think edge cases like
this were important. For instance, Renesys keeps -every- update ever,
so if Provider 1 ever flaps, Rensys will see Provider 2. Also, when
looking for the number of providers, a "backup path" may not be
relevant since no packets take that path.
More importantly, I thought the point of the talk was to show that the
table was growing during the recession and people were still getting
more providers. The result is a curve, not a hard-and-fast number.
Corner cases like the one above are barely noise, so the curve it
It is true that finding peering edges with things like route-views is
problematic at best, so finding ASes with one transit plus peering
might be problematic. But since I do not think that was the point of
the talk, I do not consider that problem.
If anyone who still thinks the problems with finding transit edges
somehow make the talk 'bullshit' could clarify their position, I would
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