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Re: Katrina Network Damage Report

  • From: Todd Underwood
  • Date: Sat Sep 10 08:05:00 2005

randy,

On Sat, Sep 10, 2005 at 05:49:59PM +0700, Randy Bush wrote:
> this report repeatedly uses the term "outage."  how is that
> determined/measured?

i think this is covered in the report several times, but i'm sorry if
it wasn't clear.  this is based on work that we've done for a while
(some of which was presented at nanog30:
http://nanog.org/mtg-0402/ogielski.html).

the general idea is:  take a large peerset sending you full
routes, keep every update forever, and take a reasonably long (at
least a month or two) time horizon. calculate a consensus view for
each prefix as to whether that prefix is reachable by some set of
those peers.  an outaged prefix is one that used to be reachable that
not no longer is.  in other words, one that has been withdrawn from
the full table by some sufficiently large number of peers.  

we exclude single-peer outages and outages that only affect a few
peers through some reasonable thresholding.

make sense?  that's the general idea.  the implementation is obviously
a *lot* more complicated.

t.

(i'm sure the question of covering prefixes will come up shortly and
i'll address it when/if it does). :-)

-- 
_____________________________________________________________________
todd underwood
director of operations & security
renesys - interdomain intelligence
[email protected]   www.renesys.com