Applies To:
  • CitectSCADA
  • Windows XP
Summary:
Normally doing this requires you to have all IP addresses on the interface as static (ie you cannot have DHCP + a static IP on the one interface).
However it is actually possible to configure one interface to have a DHCP assigned IP address plus a static IP address on the same interface. All it requires is some very simple registry editing.

An example of why you might want to do this is where you have your PC configured on your company LAN via DHCP. You have a device that comes preconfigured on some default IP addess like 192.168.0.100 and this does not match the subnet that you have been assigned via DHCP. In that case, even if you plug this into the same physical network, you will not be able to access it. However if you add an IP onto your interface that is in the same subnet (eg 192.168.0.200) then you will be able to directly access the device, without losing access to the other resources available on your companies subnet. 

Normal approach for having multiple IP addresses on the one interface. (cannot use DHCP, only multiple static addresses)
  1. Open Control Panel, Network Connections.
  2. Right-click the connection (the default is usually called “Local Area Connection”), then select properties.
  3. Select “Internet Protocol (TCP/IP)” and click properties.
  4. Make sure you select “Use the following IP Address” and enter the details for the primary address.
  5. Click “Advanced” then click the “IP Settings”. This is where you can add additional IP addresses.
  6. After configuring the additional addresses you can confirm the configuration through the normal “ipconfig” command (Start->Run->cmd. Then type ipconfig, enter).

How to have DHCP for first address then a static IP for additional addresses

  1. Follow the steps above however at step 4, select “Obtain an IP address automatically”. You will note now that if you click on the “Advanced” button that you can not add additional IP addresses as before. Instead it says “DHCP configured.
  2. Open the registry editor (Start->Run->Regedt32)
  3. Navigate to: [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Interfaces\{27C3A9EB-F837-4DE1-ADAC-854AE98CE288}]
    Note that the GUID for your own connection will not be the same as above. There may be a number of these under the Interfaces branch. Find the one that represents the network connection you want to modify.
  4. Double click the “IPAddress” key.
  5. In the dialog box enter your additional IP addresses, making sure each is on a separate line. Make sure you leave the first line the same as it was. Click Ok.
  6. Double click the “SubnetMask” key.
  7. In the dialog box enter your additional subnet masks, making sure each is on a separate line. Make sure you leave the first line the same as it was. Click Ok.
  8. Close the editor.
  9. Back in Control Panel, Network Connections. Right-click the connection, then select disable. Then enable.
  10. Verify your settings by running “ipconfig” as described above.

Notes: If you define two IP addresses on one interface, only the first is dynamically registered with the DNS server. Normally this is not of concern as the first (or DHCP assigned) address is the one you want registered in the name server. However to do this, you need can create the MaxNumberOfAddressesToRegister in the registry (at the same location as above) and set it higher than the default of 1.
http://support.microsoft.com/kb/246804/en-us 

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