Freebsd 5.3-stable natd multiple external ipadress

[Mattias Nordlund]

Hi,
I have a problem .
Freebsd 5.3 Stable
Natd
Ipfw

external interface = fxp1
internal interface = fxp2

I have three external ipadress on fxp1
81.10.5.2 /29
81.10.5.3 
81.10.5.4 

On the fxp2 (internal interface) I have :
192.168.1.0/24
192.168.2.0/24
192.168.3.0/24

I need to route the packets from my internal net to the correct external
ipadress.
Something like:
iptables -t nat -A POSTROUTING -s 192.168.1.0/24 -j SNAT --to 81.10.5.2
iptables -t nat -A POSTROUTING -s 192.168.2.0/24 -j SNAT --to 81.10.5.3
iptables -t nat -A POSTROUTING -s 192.168.3.0/24 -j SNAT --to 81.10.5.4

How can I do that with ipfw and nat ?
Heeelp 


Regards,
Mattias