I have a registered subnet 1.2.3.0/29
and an internal subnet 192.168.1.0/29
The router has INT_OUTSIDE_IP=1.2.3.2

I want to map .3,.4,.5, and .6 on 1.2.3.0 to 192.168.1.0, respectively.

I think I just need to do something like

iptables -A PREROUTING -t nat -p tcp -d $INT_OUTSIDE_IP --dport $PORT \
-j DNAT --to $SERVER_IP:$PORT

for each IP and port.  When I do this, do I need to assign each IP
to a subinterface on $INT_OUTSIDE (eth0:1, etc) or does iptables
automagically grab the IP for me?  Also, is this the best way to do it or
should I be going about it differently?

-Brian