This post explains how to use the packet tracer function to check NAT settings.
The key takeaway point for me was the following:
With Packet Tracer (PT) we can inject real packet into the ASA forwarding plane and see what’s going on. For NAT we can have three sections in the PT output (called Phases):
- NAT – shows how the source of the packet will be translated
- UN-NAT – shows how the destination of the packet will be translated
- NAT RPF-CHECK – shows how might/should source of the returning packet be translated (RPF – Reverse Path Forwarding)