On Thu, Jan 9, 2014 at 1:45 PM, John Levine <johnl@xxxxxxxxx> wrote: >>> It looks like the sites John talked to are multihomed, NOT doing >>> routing at their edge (??), and yet wanting to filter? I don't think >> >>that's not clear, from john's description at least. > > I can ask (the meeting's not over yet) but I gather that these are > multihomed customers who don't do BGP. The ISP knows what ranges it's > routing to the customer, but it doesn't know what ranges are routed to > the same customer by someone else. if they don't do bgp .. .then you'd expect only static routing and thus you know exactly what they ought to be sourcing. There are pathological (aka: stupid) cases of multihomed to 2 isps, getting static-routing of each isp's PA space on only that one ISP... and default routing up both pipes... but really that's just broken and dumb, so getting customers to fix this by filtering is a fine answer. -chris