I am by no means an expert, but shouldn't it be possible for the source's ISP to tell whether the source address is spoofed? edit: Looks like the OP managed a

I am by no means an expert, but shouldn't it be possible for the source's ISP to tell whether the source address is spoofed? edit: Looks like the OP managed a better explanation than I could since I loaded the page. Please disregard.