jimp,
Thanks for that. My brain was getting confused with the terminology rather than looking at what is happening when these settings are set and applying the correct perspective. I have confirmed that this works.
Am I correct in my assumption that in a 1:1 rule the ip or subnet entered in the "Destination" section is really source or destination depending on what end initiates the connection? Therefore if I only want this rule to apply when traffic is to or from 172.21.0.0/24, I would enter 172.21.0.0/24 in the "Destination" section, correct.
Now is there a way to create a directional NAT to do the same without being limited to specific ports and protocols?
Thanks,
Rhongomiant