What triggered the filter was the observation that in the blocks freshly allocated by all three registries were very poorly aggregated. More annoyingly, those allocated to Sprint's principal peers (most notably Internet MCI) demonstrated the worst aggregation; in one case a /14 was announced almost exclusively as prefixes no shorter than 19 bits.

What's interesting is Sprint's filters have encouraged InternetMCI's customers to clean things up more than Sprintlink's customers. As an experiment, I removed my filters last night. In general my filters are more generous than any Mr. Doran used, mostly blocking 'mistakes' like /32 prefixes. What I found was the four top providers appearing in the previous filtered paths in order were, total of 1074 filtered routes 227 Sprint 225 UUNET 97 AARNET 92 MCI Sprint has taken over the number 1 spot, and MCI dropped to number 4, from the point of view of my BGP routers. Although MCI still seems to be well represented amoung the very, very long (>/30) prefixes. But this may simply be due to someone else filtering out extremely long prefixes before they reach my BGP routers. So you should view these as lower bounds. Things may be worse. What was even more interesting was number of routes accounted for by >/24's in 192-210 space and >/16's in 128-191 space was more than any of the CIDRizing suggestions in Tony Bates weekly CIDR report. Some people seem to view CIDR as an opportunity to subdivide their traditional 'Class B' networks. I would classify most of these announcements as 'mistakes' because they usually also announce the supernet, and have the same path. Here were some of the extreme examples. 168.248.0.0/30 3561 i 168.249.0.0/30 3561 i 198.203.196.144/32 3561 i 203.38.0.144/30 3561 1221 ? 203.38.0.148/30 3561 1221 ? 207.65.182.111/32 3561 i -- Sean Donelan, Data Research Associates, Inc, St. Louis, MO Affiliation given for identification not representation