My understanding is that IP address spoofing would not be possible if all ISPs would be doing egress filtering. That is, each ISP would not allow any IP packet to go outside of it's network if it sees a source IP, which does not belong to the source sub-network.
But what is the modern empirical evidence of it actually happening? How many "spoofed" packets manage to go far enough on the Internet highways that they can reach the destination, given that this destination is on another continent for example.
I understand that for a spoofing attempt to be effective, it needs to make sure that a response is also routed to the "malicious" destination. But I'm more interested in the initial "request" IP packets and the "real life" experience of spoofed packets on the Internet managing to get far outside the real source ISP.