We (at NIST) performed some additional data analysis to characterize
AS_SETs in BGP updates in RIB entries. The results can be found
in the slides at this link:
http://www.antd.nist.gov/~ksriram/AS_SET_Aggregator_Stats.pdf
This work was presented at the IETF SIDR WG meeting in Maastricht in July 2010.
Please look at mainly slides #3 and #4.
The findings are consistent with Olaf Maennel's (that Randy posted) in term of how
few updates have AS_SETs in them.
We additionally looked at the the question of -- when AS_SET is present, how often
does the ASN in the AGGRGATOR field in the update matches the originating AS?
This question has relevance to origin AS validation using ROAs in RPKI --
to try to propose how origin validation can be done if AS_SET is present in an update.
Please look into my slides if you are interested in the details.
I will be happy to answer any questions.
Currently, the push from several of us (Warren Kumari, Randy, many others -- I support it too)
is to deprecate AS_SETs altogether in future BGP enhancements such as RPKI.
This would mean an update will not pass origin validation
(in fact, origin validation using ROAs will not even be attempted) if AS_SET
is present in an update.
Comments/reaction/feedback to this from ops people who currently use AS_SETs
would be very useful.
(This would be good for discussion of Warren's draft in the IDR WG.
http://tools.ietf.org/html/draft-wkumari-deprecate-as-sets-00 )
Sriram