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Microsoft Virtual PC Tip – Using the Microsoft Loopback Adapter

Microsoft Windows 2000 and XP (and probably others) ship with a built-in network interface driver called the "Microsoft Loopback Adapter" that lets you create a local-only network interface device. This adapter can be extremely useful when you are doing development testing using Virtual PC and want to isolate your Virtual PC's from your main network.

For instance, let's say that you want to test a SharePoint Portal configuration with a separate front end web server, a separate index and job server, and a separate database server. Using Virtual PC you would configure the network adapter of your virtual machine to use the Microsoft Loopback Adapter for each virtual machine in your virtual server farm. When you spin up all of your virtual machine instances, they would only be able to communicate among themselves and any traffic would be isolated and limited to your testing environment.

To configure your Microsoft Loopback Adapter under Windows XP, do the following:

  1. From the Control Panel, select "Add Hardware"
  2. Select "Yes, I have already connected the hardware"
  3. Select "Add a new hardware device" (at the bottom of the listbox)
  4. Select "Install the hardware that I manually select from a list (Advanced)"
  5. Select "Network adapters"
  6. Select "Microsoft" as the manufacturer and "Microsoft Loopback Adapter" as the adapter

From within Virtual PC

  1. Select your virtual machine
  2. Go to the Settings (either right-click the VM and select "Settings" or from within a running instance go to the "Edit" menu and select "Settings)
  3. Click the "Networking" setting
  4. For your network adapter, select "Microsoft Loopback Adapter"

Now, you should be able to see your other running Virtual PC instances that also share the same loopback adapter!

Note: If you run into a problem where you can't select the Microsoft Loopback Adapter", you'll need to verify that 1) the "Virtual Machine Networking Services" are installed for the loopback adapter, and 2) if they are, and you still can't select the adapter, uninstall the service and then reinstall the service (by pointing to the Virtual PC installation directory under Utility/VMNetSrv).

Happy Virtual PC'ing!


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4 Responses to Microsoft Virtual PC Tip – Using the Microsoft Loopback Adapter

  1. Ann Paulus says:

    We are testing a CRM software that utilizes the Microsoft Loopback adapter on the client pc. This allows the rep to use the application when not connected to the network. If the machine is connected to the network, everything works fine. We have seen when the network connection is just unplugged, the software gets a “socket” error which is related to the loopback adapter. If you check the connection, the adapter does show enabled but it is not being recognized. Has anyone seen this or any ideas on how to fix? I’m not 100% that unplugging the connection without proper shutdown is causing the problem. Any help would be appreciated. Thanks!

  2. Ankur says:

    Dear sir
    please tell me how to uninstall microsot loopback adapter in windows xp.

  3. Pat Pelletier says:

    There was one small hitch – when you install the loopback adapter, it doesn’t automatically enable TCP/IP. Once I enabled it on the loopback on the host and configured IP it all worked well.

    Thanks for the tip. This will be very useful in testing out our apps in a DEV environment.

  4. Nilesh Mehta says:

    I am trying to setup a VPC environment as follows:
    1. Host PC with Win2K3 SE + AD + Domain Controller + SQL 2000 SP3
    2. Virtual PC with Win2K3 SE and SPS 2003.

    I tried your loopback adapter solution. It can communicate with the host pc via a ping but my virtual PC cannot communicate with the domain controller on the host pc. Can you please help me with that? Even though during the install the virtual PC was able to join the domain on the host PC, when I try to add a domain user to the administrators group in the VPC, it cannot find the domain. It does not know where the domain is.

    Appreciate your help.
    Thank you & Best Regards,
    Nilesh Mehta

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