IP Passthrough is a useful feature if a host computer or server on the Local Area Network needs to have access into it from the internet with a real public IP address. With IP Passthrough configured, all IP traffic, not just TCP/UDP, is forwarded back to the host computer. This can be necessary with certain types of software that do not function reliably through Network Address Translation.

In this configuration, the local PC will share the Public IP addressing information with the WAN side of the router. Also, this computer will have access to other resources on the LAN while it is in this mode.

This technote will guide you through the setup process for IP Passthrough in your 3300 Series Gateway.

Please Note: Once you have configured the router for IP Passthrough, you can no longer ping or remotely manage the Netopia router via the WAN IP Address!

Please Note: If your router is currently running Netopia Enterprise Firmware version 8.0.10 and later, this technote is not applicable to you. See NQG_025 IP Passthrough for Netopia Enterprise gateways.

Firmware Reference

• v7.3.0 R0 and later -- Netopia 3300 Series

Before You Start

Browse into the Netopia's web interface at http://192.168.1.254 (if using the default IP setting). If your network has a different IP addressing scheme, modify this accordingly.

Login with the admin user name and password. Admin login is required to save changes. If you are unsure of this, contact your network administrator.

Once logged in, click on the Expert Mode link in the left-hand side menu (if that link is visible). In the Expert Mode Confirmation screen click on Ok to continue. This menu bar will be visible at the top of your screen if you are in Expert Mode.

Remember to click the Submit button to save any entries. Hitting the back button without clicking Submit will undo any changes.

Once you have completed your configuration, click on the symbol in your upper right hand corner to validate the changes. Then click on Save and Restart.

The Netopia Web GUI Home Page in Expert Mode (Firmware v6.3 and later)

IP Passthrough Configuration

1. From the Main Menu, click on Configure.
2. Click on Advanced.
3. Under the NAT heading, click on Default Server.
4. Click on the drop-down and select IP-Passthrough.
5. Click on the Submit button. (You must click on the Submit button to retain this change!)
   
PLEASE NOTE: In the Default Server configuration box, you will see an option for DHCP Enable. This is a separate function from the LAN DHCP server assigning addresses to any other computers on your local network. For the purposes of this discussion, this checkbox needn't be enabled.
However, if you have a dynamic account, click here for recommended alternate instructions.
6. Click on Submit. (You must click on the Submit button to retain this change!)



7. If this completes your configuration, click on the in the upper right hand corner. This will validate that the settings are legal for your network.
8. If you get Validation Passed, click Save and Restart in the menu. If it doesn't validate the change, a message will indicate the reason. It must be corrected before the configuration change can be applied.
9. This completes the configuration of the Netopia for IP-Passthrough.
10. The router will reboot and should be back online in 45-60 seconds.

Now you will need to manually configure the workstation with the Public IP Address and subnet mask that has been assigned to the router's WAN interface for this session.

The default gateway of this workstation will be the same as the default gateway of the Netopia router. That default gateway is the next hop out from the WAN side of the Netopia. Be sure to include the DNS information as supplied by the ISP in the configuration of the TCP/IP properties of this computer.

PLEASE NOTE: When configured in this manner, it will be necessary to reconfigure the TCP/IP properties of the PC whenever the WAN IP Address of the router changes. The IP Address of the computer must match that of the router. This IP Address can change during a period of internet inactivity (typically 30 minutes or longer), or if the router is rebooted.

Configuration for Dynamic and PPPoE Accounts

PPPoE accounts typically have a dynamically assigned WAN IP address. The most efficient way to utilize the IP Passthrough feature would be to have the router use DHCP to assign the address to a specified MAC Address. These instructions will outline the necessary steps.

Continuing after Step #6 above:

7. Check the box to enable DHCP. A new screen will open for Host Hardware Address configuration. This is also commonly referred to as a MAC Address. This is a value hard-coded to the computer as an equipment identifier.

   

   If you have a PC:

   Open a DOS Prompt. At the prompt, type ipconfig  /all. The information generated gives a detailed summary for network settings. You are looking for a value for the Physical Address. This will be in a hexidecimal format, and has the same letter/number pattern as you saw in the DHCP-enabled Default Server screen.

   

   If you have a Macintosh:

   Running OS 9 and earlier, go into the Control Panels, TCP/IP, and click the Info button. The Hardware Address is displayed right below the IP Address for that computer.

   As of OS 10, go into your Systems Preferences -> Network -> Ethernet for this value.

8. After entering this value, click on the Submit button.
9. Click on the in the upper right hand corner. This will validate that the settings are legal for your network.
10. If you get Validation Passed, click Save and Restart in the menu. If it doesn't validate the change, a message will indicate the reason. It must be corrected before the configuration change can be applied.
11. This completes the configuration of the Netopia for IP Passthrough.
12. The router will reboot and is now set to share the Public IP Address with the computer which has been specified to receive that address.

Conclusion

You've now configured your Netopia 3300 Series Gateway for IP Passthrough, which allows one PC on your LAN to share the router's Public IP Address. This can be especially useful for certain types of interactive games that don't work well through Network Address Translation and need a public IP address to function properly.

CAUTION: Be advised that the host computer is exposed to the internet, and this does have ramifications of network vulnerability. Even though NAT is enabled, this machine is on a public network. Adequate precautions should be included in any configuration to protect the network from unauthorized intrusion.