One-way Cable Modems

Reference Manual

HOW TO configure NAT32 for the Surfboard Cable Modem

One-way cable modems connect to your machine via a standard Ethernet Adapter, but use this Adapter for incoming traffic only. Traffic to the Internet leaves your computer via the Windows Dial-Up Networking Adapter. The following example shows how to configure a Surfboard one-way Cable Modem setup.

Note that some one-way cable modems actually have their own telephone modem built in. The cable modem itself handles the dial-up connection and your Windows system never interacts with that connection. Windows (and NAT32) handle such cable modems as if they were standard Ethernet Adapters.

Windows Setup

Before you run NAT32, please set up your Windows System as follows:

Install an Ethernet Adapter for your private LAN.
Configure it to use a fixed IP address like 192.168.1.1, a Subnet Mask of 255.255.255.0 and no gateway.
Install an Ethernet Adapter for your Cable Modem.
Configure it to use a fixed IP address like 10.1.1.1, a Subnet Mask of 255.255.255.0 and no gateway.
Reboot Windows

Be sure you have specified a DUN Connection in accordance with your ISP's instructions. Now start that DUN connection.

NAT32 Setup

Before you run NAT32, be sure the DUN Connection to your ISP is up and running. Open a DOS Box and ping your private machine(s). Also ping a few machines on the Internet (like www.nat32.com). If any of these pings fail, do not attempt to run NAT32, consult a local expert for help with configuring Windows TCP/IP networking.

Also, before you run NAT32, be sure the WinPkFilter Driver is installed.

Now start NAT32 as: nat32.exe ppp 2

Alternatively, start it as: nat32.exe
and then select "Dial-Up Networking Client" and "2 LAN Interfaces" in the NAT32 Options Dialog Box. Click Continue.

NAT32 will then present the first Interface Configuration Dialog Box (it will be for Logical Interface 2, your first LAN Adapter). All of the suggested settings in this Dialog Box should be correct, so simply click OK.

NAT32 will then present the second Interface Configuration Dialog Box (it will be for Logical Interface 3, your second LAN Adapter). Again, all the suggested settings in this Dialog Box should be correct, so simply click OK.

The NAT32 Console will then appear and NAT32 is almost ready to run.

If the two Configuration Dialog Boxes do not appear, please terminate NAT32 and erase the files netcfg2 and netcfg3 in your NAT32 directory. Then start NAT32 again.

Now the tricky bit:

If the private LAN Adapter (192.168.1.254) is the first Adapter to show up in a NAT32 Interface Configuration Dialog Box, it will be NAT32 Logical Interface number 2. Then do the following:

Terminate NAT32 and open the file startup (in your NAT32 directory) with Notepad or Edit.
Modify the command ipmapa so that it reads: ipmapa 2
Add the command: sets 2
Add the command: simplex 3
Be sure to add those two commands before the final shell command in file startup.

If the private LAN Adapter (192.168.1.254) is the second Adapter to show up in a NAT32 Interface Configuration Dialog Box, it will be NAT32 Logical Interface number 3. Then do the following:

Terminate NAT32 and open the file startup (in your NAT32 directory) with Notepad or Edit.
Modify the command ipmapa so that it reads: ipmapa 3
Add the command: sets 3
Add the command: simplex 2
Be sure to add those two commands before the final shell command in file startup.

Now restart NAT32 as before and all should be well. Go to another machine, and, after configuring it to use 192.168.1.254 as its Gateway and DNS address, you should have Internet connectivity from that machine.

If you encounter any problems, please generate an info.txt file by clicking Help/Info.txt in the NAT32 Console and waiting for the Shell Prompt (%) to reappear. Then e-mail the info.txt file to NAT32 Support. Please contact us first to obtain our current e-mail address: Contact Support.