NAT + Internet Sharing – possible with only one NIC card?

After reading an article entitled ‘Squeezing NAT Out of Panther Server’ (http://www.oreillynet.com/pub/a/wireless/2003/11/25/nat_panther.html) so many times, and others to, but am not having any luck setting this up Any chance of a bit of help??

Let me just outline you on my setup:
G4 running 10.3.4. It has one NIC card, and a USB ADSL modem. The NIC is hooked up to an ethernet hub, which is hooked up to all the other Macs in my house.

I have read a few other articles which detail how to set this up when you have two NIC cards (one with an ethernet modem attached, and the other connected to a hub – the LAN) but as you know I only have the one NIC.

In this article it talks about duplicating the Configuration for the built in ethernet and renaming it Private Network, but doesn’t really go in to much detail as to what this is for. I am assuming that in doing this, you are binding two IP address to the one card… Am I right?

Currently I have this…
System Preferences -> Network -> USB-Modem
Configure using: PPP
Id Address: 81.152.12.123 (assigned dynamicly by ISP)
Router: 213.123.79.47 (assigned dynamicly by ISP)

System Preferences -> Network -> Built in Ethernet Card
ip: 192.168.0.1
subnet: 255.255.255.0

System Preferences -> Network ->Private Network
ip: 192.168.3.1
subnet: 255.255.255.0

Server Admin -> DHCP:
start address: 192.168.3.2
end address: 192.168.3.254
subnet: 255.255.255.0
Network Interface: en0
Router: 192.168.3.1

I then turned everything on in the firewall for the 192.168-net

And created the advanced rule as suggested
(I actually created two: one with source=any, destination=192.168-net
and one the other way round, ie. source=192.168-net, destination=any.
I did this because in your description it says to do it one way, yet in the
picture it is the other way round!).
Could someone please clarify what it should actually be??

I manually edited the /etc/hostconfig file as suggested.
(enabled IP FORWARDING)

Then I turned on NAT

Now, From my laptop, which is set up to use DHCP:
It’s IP get’s assigned to 192.168.3.2 (so DHCP is working fine)
I can ping 192.168.0.1 succesfully
I can also ping 192.168.3.1 succesfully

however, when I try to ping an outside address, I get no response…
Here is a short extract from my firewall log after trying to ping an outside address:

Jul 11 15:31:44 localhost kernel: ipfw: 1000 Accept TCP 127.0.0.1:311 127.0.0.1:50104 in via lo0
Jul 11 15:31:44 localhost kernel: ipfw: 1000 Accept TCP 127.0.0.1:311 127.0.0.1:50104 out via lo0
Jul 11 15:31:44 localhost kernel: ipfw: 1000 Accept TCP 127.0.0.1:311 127.0.0.1:50104 in via lo0
Jul 11 15:31:44 localhost kernel: ipfw: 1000 Accept TCP 127.0.0.1:50104 127.0.0.1:311 out via lo0
Jul 11 15:31:44 localhost kernel: ipfw: 1000 Accept TCP 127.0.0.1:50104 127.0.0.1:311 in via lo0
Jul 11 15:31:44 localhost kernel: ipfw: 12369 Accept UDP 192.168.3.2:52037 194.74.65.69:53 in via en0
Jul 11 15:31:45 localhost kernel: ipfw: 12369 Accept UDP 192.168.3.2:52038 194.74.65.69:53 in via en0
Jul 11 15:31:45 localhost kernel: ipfw: 12369 Accept UDP 192.168.3.2:52040 194.74.65.69:53 in via en0
Jul 11 15:31:45 localhost kernel: ipfw: 12369 Accept UDP 192.168.3.2:52041 194.72.9.38:53 in via en0
Jul 11 15:31:45 localhost kernel: ipfw: 65000 Deny TCP 81.152.7.157:3162 81.152.12.123:135 in via ppp0
Jul 11 15:31:46 localhost kernel: ipfw: 1000 Accept TCP 127.0.0.1:311 127.0.0.1:50106 out via lo0
Jul 11 15:31:46 localhost kernel: ipfw: 1000 Accept TCP 127.0.0.1:311 127.0.0.1:50106 in via lo0
Jul 11 15:31:46 localhost kernel: ipfw: 1000 Accept TCP 127.0.0.1:915 127.0.0.1:1033 out via lo0
Jul 11 15:31:46 localhost kernel: ipfw: 1000 Accept TCP 127.0.0.1:915 127.0.0.1:1033 in via lo0
Jul 11 15:31:46 localhost kernel: ipfw: 1000 Accept TCP 127.0.0.1:311 127.0.0.1:50106 out via lo0

What have I done wrong?? / What must I do differently?

many thanks
Tom Kirkpatrick