External IP Inbound what computer NAT to

[senseii]

I have an external IP address that I packet capture with the pfSense. How can I tell what device in my network the external IP went to? pfSense firewall just lists my isp ip address, not my internal device it went to.

[senseii]

To expand on this question it's possible that what is happening is a SYN scan is occuring out in the wild and my router is included in that mass scan.