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Product Selected: Think & Do
Category Selected: Communications

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Question: I have 2 or more network cards installed in a computer where both are using TCP/IP protocol. I can PING the WinPLC, but cannot connect using ESP.
Answer: When 2 or more network cards are installed in a computer, this is referred to as a "multi-homed" system.
The protocol manager needs to know which network card to send the TCP/IP packets over, and the WinPLC needs to know which one to respond to. This presents a requirement known as "IP Forwarding".




There are (2) requirements for resolving this issue.
  • You must enable IP Forwarding. This is handled differently for Windows NT and Windows 2000.



    For Windows NT:
    Go to Control Panel->Networks->Protocols, and choose TCP/IP. Then click on the Properties button, and a dialog shall appear. Click on the tab labelled "Routing", and place a check mark next to "Enable IP Forwarding", then choose OK. Choose OK again to close the Network properties dialog, and reboot as instructed by the Windows NT.



    For Windows 2000:
    WARNING: Using Registry Editor incorrectly can cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that problems resulting from the incorrect use of Registry Editor can be solved. Use Registry Editor at your own risk.


    For information about how to edit the registry, view the "Changing Keys And Values" Help topic in Registry Editor (Regedit.exe) or the "Add and Delete Information in the Registry" and "Edit Registry Data" Help topics in Regedt32.exe. Note that you should back up the registry before you edit it. If you are running Windows NT, you should also update your Emergency Repair Disk (ERD).



      Steps:
    1. Click on Start->Run, and type 'regedit' and press ENTER
    2. Navigate to the key [HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesTcpipParameters]
    3. Find the value "IPEnableRouter", and double click on it
      You will now get an opportunity to change it's value. Change it to '1' (without the quotes) to enable IP Forwarding.
    4. Reboot the machine to refresh the registry cache.

  • After enabling IP Forwarding, you must set the WinPLC's Default Gateway address to point to the Static IP Address of the Network Card that is connected to the WinPLC. This can be done through the standard "Reset using IPX", or if the WinPLC is available, through "Configure..." from ESP.

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    FAQ ID: 893
    Question: I'm using Think&Do Live/Studio and I'm trying to connect to an H2/H4/T1H-EBC. But I keep getting errors.I have NetEdit and it can see the EBC with no problems. What could be wrong?
    Answer: This problem is usually the result of having 2 NIC( Ethernet) cards installed in the same PC.

    If this is the case you need to access the network settings of the NICs specifically the Protocols that are assigned to each card.
    On the NIC that is used for your company you should disable/remove/uncheck the NWLink IPX/SPX protocol if installed. Then on the NIC card that is dedicated to the Think&Do system you should enable/install/check the NWlink IPX/SPX protocol and the TCP/IP protocol.
    You should also check to make sure that an address has been set on the EBC by toggling at least one dip switch to the ON position.
    FAQ ID: 900