This document describes how you can configure an Alcatel SpeedTouch Pro ADSL modem not to use NAT anymore. This process is often called DHCP SPOOFING. The public IP will be sent to your machine by DHCP therefore eliminating NAT. It is also for setups where combination of an Ethernet gateway routers which do not have PPTP dialer support are in placed. Doing so will enable you to configure an internal router or a server that has routing software installed and have it receive an IP address from your ISP – instead of having the dialer obtain the address for you.
The difference between DHCP SPOOFING and BRIDGING (described here Configure Alcatel SpeedTouch Pro to Act as a Transparent Bridge) is that with bridging the end-machine/router does the dialing, and so it gets the real IP address from the ISP. With spoofing the modem dials for you, receives the IP address from the ISP, and then gives it to the end-machine/router.
This method will work if one of the following assumptions is true:
- Your modem is connected to the Internet and another computer is connected to your modem.
- Your modem is connected to the Internet and you have a router that is connected to the modem. This router must have NAT capabilities. The router will then be connected to a hub/switch, and to it other computers will connect.
- Your modem is connected to the Internet and you have a server computer that is connected to the modem. This server must have Routing and NAT capabilities. The server will then be configured with another NIC, and to it you connect another computer.
- Your modem is connected to the Internet and you have a server computer that is connected to the modem. This server must have Routing and NAT capabilities. The server will then be configured with another NIC, to which you will then connect a hub/switch, and to it other computers will connect.
Make a note of the fact that the modem will stop acting as a router with NAT/PAT which means that you’ll have to connect it to a router or server that has NAT capabilities. Without such configuration you won’t be able to connect to the Internet.
Note: This configuration tip will only work in the PRO modem or on a HOME modem that was upgraded to PRO: Upgrade from Alcatel SpeedTouch Home to Pro.
- The ADSL cable goes to the splitter.
- The ADSL modem is connected to the splitter.
- The ADSL modem is configured as PRO.
- NAT is disabled on the modem.
- The Ethernet cable from the modem is connected to the router (or server with RRAS and NAT
- The router / server is connected to the switching hub.
- All PC’s are connected to the switching hub.
Disclaimer & Warning
Messing with the software settings of your modem and/or messing with the registry or internal settings of your operating system can render your modem or operating system useless. Read the whole article and manual before you do any changes. Following these steps might work for you. It did for me and for many others, but that does not necessarily mean they will! I take no responsibility for anything bad that might happen to your OS or modem, and since you’re on your own – Do not ask me for help! It’s your modem!
Applying this hack will definitely VOID WARRANTY! If you are not experienced with tricks like these STOP NOW! Besides, some ISPs might stop supporting you if they find out that you messed up with your modem.
Configure your modem as Pro
You’ll have to configure the modem as Pro. If you have an Alcatel SpeedTouch Home please follow this guide: Upgrade from Alcatel SpeedTouch Home to Pro.
Step One – Configure your modem
You’ll have to disconnect from the ADSL service to configure the following settings, so maybe now’s a good time to print this screen.
Connect to the modem via the web interface on http://10.0.0.138.
You’ll get a screen like this one:
Go to the PPTP menu and remove all entries. Apply and Save the changes.
Go to the PPP menu and remove all entries. Apply and Save the changes.
Go to the Phone Book menu and remove all the entries. Apply and Save changes.
Go to the CIP Interfaces and delete all entries. Apply and Save all.
Go to the Bridging Ports menu and delete all entries. Apply and Save all.
Name ‘DHCP_SPOOF’ VPI=8 VCI=48 Type=ppp
Save the changes.
Note: Some European ISPs have other VPI/VCI settings. Please contact your ISP for more details if you cannot make it work with the above settings. Note that is you did get the settings right – they will have a yellow color.
Read the Upgrade from Alcatel SpeedTouch Home to Pro – Reader Notes article for more info on some of the most used settings for world-wide ISPs.
Go to the PPP menu screen and add a new entry for the ‘DHCP_SPOOF’ with a type of ‘vc-mux’.
Save the changes.
Notice that the STATE condition should be ‘Down’ for now (not ‘Up’ or ‘Trying’).
Now configure the new ‘DHCP_SPOOF’ entry with the following settings:
User=username@Iisp (CAPITAL ‘I’ and the name of your ISP) Password= (provided by your ISP) Connection Sharing = Everybody Destination networks = All networks Specific network = Address translation (NAT-PAT) = NOT selected Primary DNS and Secondary DNS = (provided by ISP) Local IP and Remote IP = none Mode = DIAL-IN Idle time limit = LCP echo = selected PAP = ACCOMP = selected
Make sure you DO NOT select the checkbox near the Address Translation (NAT-PAT). Make sure that the Mode is configured as Dial-In.
Apply and save these changes.
Notice that in the PPP menu screen you’ll see the STATE will remain ‘DOWN’ until you configure the router or another computer to receive it’s IP settings automatically. It can take a while before the modem connects and changes to the ‘ON’ state.
You can also go to the PPP Dial-in Connections menu and see your entry there. You can then manually dial the connection and see if it’s STATE is ‘UP’. If it does not change, check your settings.
Go to the DHCP Server menu. Select DHCP Server.
Click Advanced and select DHCP spoofing. You should then change the ‘Timeout waiting for PPP linkup indication’ from 4 to 10 seconds. Apply and Save all changes.
Go to the DNS menu and select ‘Server Active’.
Apply and Save all changes.
Step Two – Configuring the workstation / router / server
If it’s a workstation that’s connected directly to the modem you should configure it’s NIC to obtain it’s IP address automatically (each OS has it’s own phrasing of this feature).
I think you know how to do that by now. If you’ve got amnesia here are a few screenshots of a Windows XP workstation. Figure it out on your own.
You configure the DNS server to be the same as the IP address of your ISP’s DNS server, or if you want – to be the same as the inner IP address of the modem itself.
If that computer also acts as a DC then it must already have an installed DNS service. With that said all you have to do is to configure forwarding between the DNS and the DNS server of your ISP. See the Active Directory pages on my site for more info on AD requirements – Active Directory Installation Requirements, How to Install Active Directory on Windows 2000 and How to Install Active Directory on Windows 2003, and the DNS pages for info on DNS Forwarding – Configure DNS Forwarding on Windows 2000 and No Forwarding or Root Hints on Windows 2000 DNS server?.
If it’s a server then you have to configure it as a router (which is beyond the scope of this lesson) with NAT capabilities. You configure the NIC that is connected to the modem to obtain an IP address automatically, and you assign a private IP address to the LAN interface, such as 192.168.0.1 and a default Subnet Mask of 255.255.255.0.
If it’s a router – you configure the WAN interface to obtain and IP address automatically. On the LAN interface you either manually configure the IP network ID etc, or you deploy a configured DHCP with all their needs.