ipfw STUN Firewall/NAT Type

[Michael C. Cambria]

Is there any documentation on what type of nat ifpw/nat is?  At present, 
I'm using FreeBSD 4.10-Stable and ipfw (not ipfw2)

For example, if rc.conf had just the bare minimum:

firewall_enable="YES"
firewall_type="OPEN"
natd_enable="YES"

what would a STUN client on a private subnet see ipfw/nat as, a Full 
Cone, Restricted Cone, Port Restricted Cone or Symmetric NAT?

I've tried with a few stun clients myself, but get conflicting results. 
  I'm interested in what ipfw/nat is meant to be?

Thanks,
MikeC