Huh? You see the packets enter the machine that's intended to receive the packets, but no one answers them? That's not a routing problem. If the packet reaches the machine that it's destined for, routing is done.

Reasons the packet is not being processed could be that the IP stack doesn't think it's destined for that machine or the firewall could be dropping the packet. Sometimes there are rules that drop packets that come in on the "wrong" interface in order to prevent an attacker from sending a packet to your public interface with a private address on it. You might want to look into that.