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Re: Active BGP Probing and large AS-sets

  • From: Lorenzo Colitti
  • Date: Thu Jun 09 10:49:13 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.


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