[c-nsp] ISP - unwanted traffic

[jack daniels]

Hi Guys,
I'm facing a issue and stuck on a thought process , would appreciate if some

way you guys can show with your experience in industry -

ISSUE ----

user X spoofs IP ADDRESS OF ISP-A and sends traffic out to internet...
now when traffic is comming back via ISP-A... I want to block such traffic
which is not orignating from my ISP...
but catch here is ---- filtering is to be done in ISP ...so putiing acl for
each users and ports is not scallable.....
Please help with any way out ...
Thanks and Regards