Here's a possibility offered for discussion for minimizing the effect of someone pointing default to you at an exchange point. This would not defeat all defaulting but might make the effect less painful. Do not carry a full routing table on your exchange point router. Only carry routes to your customers and to networks with which you peer at that particular exchange point. That way if someone sends you traffic destined for a peer that you do not see at that exchange point, like via private peering on another router or at another exchange point, your exchange point router will not have a route to it. Traffic from a defaulting network destined for one of your local peers could be forwarded to that peer directly without crossing your backbone. Also, it may help in detecting a defaulting network. If a customer of the evil defaulting network traceroutes to a destination that ends on your exchange point router and sends it to your NOC as a problem - their caught. This would work best at exchange points that are less than fully attended. -Andy