How to clear ISP traffic with OpenWrt?

Because I´m using Classify and i want the packets from my isp to end up in my sqm layer_cake CS0 tin but they end up in the highest tin... also i think cake evaluates the ingress dscps before the firewall rewrite. Someone said veth0 would be a solution but i dont know how to set that up and i cant find any usefull information.