>> eg I want to allow incoming SMTP (port 25) connections from the
>> outside through my public PPP IP address of 203.57.42.254 to an
>> internal SMTP server running at 192.168.1.218. Similarly, I want web
>> requests from the outside to go to 192.168.1.220.
>
> rdr ex0  0.0.0.0/0 port # -> In.ter.nal.IP port # tcp/udp
>
> ex0 should be your external interface, and tcp/udp can be tcp/udp, udp, or tcp.
>
> So, for http, you would add this to /etc/ipnat.conf then restart
> ipnat (assuming ae0 is you external interface):
> rdr ae0 0.0.0.0/0 port 80 -> 192.168.1.220 port 80 tcp

I tried this ipnat.conf file:

map ppp0 192.168.1.0/24 -> 0.0.0.0/32 portmap tcp/udp auto
map ppp0 192.168.1.0/24 -> 0.0.0.0/32
rdr ppp0 0.0.0.0/0 port 25 -> 192.168.1.218 port 25 tcp
rdr ppp0 0.0.0.0/0 port 80 -> 192.168.1.220 port 80 tcp
rdr ppp0 0.0.0.0/0 port 53 -> 192.168.1.219 port 53 tcp

Internal clients reach outside servers okay, but outside connections to internal servers fail.

Any more help on fixing or diagnosing appreciated.

Thanks,
Tom