NAT problem with public network

[John Angelmo]

Nickolay A. Kritsky wrote:
> Hello John,
> 
> You can use two ways:
> 1. Add 'unregistered_only yes' to your natd.conf
> 2. Run natd on xl2 with -reverse option
> 
> If I were you I would do the first one.
> 

I tried that with this rule on top
ipfw add divert natd log all from any to any via xl0

Well that handles all the packages and just then kicks out the packets 
not to 192.168.20.0/24 to the rest of the IPFW rules, should I do 
something like this instead:
ipfw add divert natd log all from 192.168.20.0/24 to any via xl0 keep-state

I simply want to only nat the right rules and let the rest of the 
packages be handled by ipfw

/John