Iptables special config

Dear all,

I have a question regarding a special configuration with iptables, I hope you can help me:
- Behind the NAT there’s a terminal with IP1 that sends a UDP packet to a host outside the NAT with IP2 (Source port=1033 Dport= 123)
- The response to this packet (due to load balancing issues) comes from a machine outside the NAT with IP3 (not from IP2!!) with Source port=123 Dport=1033

Since iptables is configured as a port restricted NAT the response packet is dropped not reaching terminal with IP1… Any idea how to make the packet reach the terminal with IP1? I know that with a full cone nat this wouldn’t happen…

Best regards,
Vitor Pinto