Active BGP Probing and large AS-sets

Thu Jun 9 14:46:25 UTC 2005

Hannigan, Martin wrote:
> Yes, but last time you said you were going to use 
> _other peoples_ ASN's to test with and allow these
> announcements beyond your borders.
> 
> Is this still the case?

The probing AS (call it Z) announces one of its prefixes to the Internet 
with an AS-path that is not just Z but Z {a,b,c...}, where a,b,c,... are 
the numbers of other ASes in the Internet.

For the technique to be useful, the numbers in the set must belong to 
ASes that actually receive Z's announcements. These ASes will not use or 
propagate the route, effectively "disappearing" from the Internet as far 
as the prefix is concerned. This causes alternate and backup paths, not 
normally visible, to become active for that prefix.

By looking at RIS and RV and the looking glasses of other ASes, Z can 
then see who propagates the prefix, where its announcements go, if other 
ASes have particular preferences for particular paths to it, and so on.

Apart from the different AS-path, the prefix is announced in the same 
way as all the other prefixes belonging to Z.

So yes, the ASes inserted in the AS-set are operated by others, and yes, 
the announcements are sent out to the Internet at large.

Regards,
Lorenzo

-- 
lorenzo at ripe.net                  colitti at dia.uniroma3.it
www.ripe.net                www.dia.uniroma3.it/~compunet
RIPE NCC        Roma Tre Computer Networks research group