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Re: Katrina Network Damage Report

  • From: Todd Underwood
  • Date: Sat Sep 10 09:26:59 2005

randy brings up two separate questions...

On Sat, Sep 10, 2005 at 07:22:34PM +0700, Randy Bush wrote:
> but what about existence of covering or more specific prefixes?
> while aggregate inferences are likely reasonable, in general,

see?  i told y'all that this would come up!  yes, covering prefixes
count.  there are many fewer covering prefixes than many most net
geeks would like to believe.  there are also many prefixes that appear
(in routing data only) to cover that do not, in fact, provide
forwarding for the more specific prefixes.

a simple analysis that only includes a covering prefix if it has
exaclty the same origination pattern (last two ASes maybe), might be
sufficient.  still no way to tell, for certain, whether the cover

our analysis didn't look at covering prefixes, but a spot check of the
outaged prefixes doesn't reveal many.  perhaps someone else would like
our list of outaged prefixes to check those for cover?

> inferring unreachability of end interfaces by looking only at
> routing data, especially multi-hop bgp data, worries me.

me, too.  that's why we didn't do that.

two issues in this second question:

1) the multi-hop issue is bogus, i believe.  i'll ignore it unless randy chooses
to say what he means here.  

2) yes, indeed.  we chose only to comment on changes in the routing
table as changes in the routing table.  inferences about
unreachability of end interfaces is left entirely to the reader
(randy, in this case).


todd underwood
director of operations & security
renesys - interdomain intelligence

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