Odd BGP AS Path

Randy Bush randy at psg.com
Thu Sep 23 14:59:07 UTC 2010

just to uncloak a bit.  when we first decided to look at deprecating
as-sets et alia, we begged olaf maennel to analyse the use thereof.  the
following is edited from internal email from early august.  we then
begged one of our number, warren, to do the dirty, and he was kind
enough to do so.  we owe him.


using data from ripe r00

years    total     real
stable  as-sets   as-sets
  7         4        2
  6         6        2
  5        20        3
  4        22        5
  3        64       16
  2       214       87
  1       875      289

years stable is how many years that as-set was announced for that

total as-sets is the number of prefixes that had any as-set.

real as-sets is the number of prefixes with as-sets which were not
singleton asns and were not private asns.

olaf scanned for ten years but none were stable for more than seven.

in ten years, 1205 different prefixes with as-sets were seen.  removing
private asns and removing singletons left only 404 prefixes over the ten

he did not check for covering prefixes, i.e. two prefixes with the same
as-set where one was a sub-prefix of the other, longer, one.

and i suspect the data are somewhat self-similar.  i.e. the 289 that
were stable for the last year may have shorter term components which
were much higher.  i.e. looking at data for a week or a day may give
higher values.

a graph which should be pretty self-explanitory may be found at


it is interesting that, at no time, i.e. in no single rib dump, were
there more than 23 prefixes with as-sets.  while this is suspicious, it
seems to be true.


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