I see some 1,927 /18 prefixes from my remote corner of the BGP world (AS 1221) and the number has been steadily growing. (http://www.telstra.net/ops/bgp/bgp-prefix-18.html) 151 of these /18 prefixes come from the old B range, and the transits carrying these prefixes include AS 1, 701, 5727 & 3561 to name but a few of the 133 AS's whose AS number appears in the paths of this set of /18 prefixes. So is /18 filtering on the old B space ubiquitous? No - it appears not. Is it common practice to filter such routes? Again the evidence appears to say no, although its hard to tell from one view of the route table how many other /18 advertisements have been filtered out. That is NOT the same as saying "Will my /18 get advertised ubiquitously?", as I suspect the answer to this latter question is "no, there are a number of transits who are applying prefix filters such that these announcements will not be carried across their networks." regards, Geoff Huston At 11/29/00 09:44 AM +0100, Guillaume, Frederic wrote:

All,

We have a couple of customers with /18 networks. Apparently, these networks are not routed over some part of the Internet because they belong to a class B range (c.f. 170.9.192.0/18) and we only route part of it (c.f. /18 instead of /16).

Is it a common routing policy to filter such routes (see Verio routing policy http://info.us.bb.verio.net/routing.html#PeerFilter <http://info.us.bb.verio.net/routing.html#PeerFilter> ) ?

Thanks for your input,

TELFORT Fr�d�ric Guillaume Tel: (+31) 20 200 70 80 Design & Planning Data Fax: (+31) 20 200 66 14 Networks & Systems Mob: (+31) 6 26 69 80 27