There were several other providers who got notes from me about prefixes that were flapping every several seconds or thereabouts. The tally so far: Polite "we have a ticket open and will get someone to fix things" from three providers (thanks ANS, BBN, EBONE). A trio of no-answer-yets, one of which has since been fixed, one of which will be fixed since I have the advantage of sharing a room with the routing guru of the NSP in question and the bigger advantage of not needing nearly as much sleep. :-) The third no-answer-yet is from a smaller provider in Europe, and I expect they'll get back to me in their morning. Finally, there was the previous reply. Sean. P.S.: Oh, I also have to thank Pushpendra Mohta of CERFNET who replied to an earlier note personally with an explanation of what was going on.