These are still likely to be IP addresses in an IP range the ISP is responsible for routing. This is the big need. ISPs need to stop packets on egress that ar

These are still likely to be IP addresses in an IP range the ISP is responsible for routing. This is the big need. ISPs need to stop packets on egress that are from IP addresses not in the ISPs network. There's no excuse for it and it would drastically undermine a sizeable number of DDoS attacks (not every DDoS, because they don't all require IP spoofing.) Unfortunately this requires ISPs to actually be responsible for the data coming out of their network, including DDoS traffic. Once you stop the spoofing, ISPs and transit providers will soon figure out which ASs are problems and start blocking them etc.