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LoopBack Issues

Loopback is necessary in some gaming applications and in Opensimulator if you are going to be running on the Hypergrid and using the viewer on the server. The usual symptoms is being unable to log in to the server after switching to a Public IP or a Dynamic DNS name. If your router does not support it, you can install a Windows loopback driver to fix the server so it can run a viewer. The loopback adapter lets a viewer on the server reach itself, as the loopback via the router is not functioning.

Manual Testing LoopBack

If you are reading this, it is probably because you already know loopback is not working and clicked the Help menu to get here. So you can skip down below and go right to "Installing the Loopback Adapter".

You can manually test for loopback by starting Opensimulator, then use a web browser to navigate to Enter port 8002 and click Check Port. This must work. if not, fix the port forwarding issues and come back and try this test again.

Your ports are known to be working now, so go get the Public IP of your system from Use a web browser to navigate to http://(Public IP):8002. Use your Public IP where it says (Public IP).

You should get an error message saying that the "knomes have absconded with the hippos". This is Opensim telling you it is working and loopback is okay. (Hippos are the mascot for Opensim.) If you get this page, loopback is working. If you do not get this page, loopback is not working in your router.

Loopback on LAN PC's ( not the server)

Other PC's on the LAN, like others outside on the WAN, will also be directed by the server to use the router's Public IP. This means that a router without loopback will break LAN PC's, too. This works for outside viewers, as the router has port forwarding on. But it will not work for the other PC's in the LAN as the router will not loop the packets back to the server.

It gets really tricky, too. I have even seen routers that will loop back from the server back to the server, but will not loop back from a LAN PC to the LAN server. Some routers also will (correctly) loopback Public IP to Private IP and Port, even when the firewall is set to stop this traffic, and some will not. The cure for other, non-server LAN PC's to is set the PC's DNS to point directly to the server, bypassing the router, by editing the hosts file.

Installing the Loopback Adapter

Click the Windows Search button and type in "hdwwiz.exe".

Run the progam that appears at the top of the search list.

In the "Welcome to the Add Hardware Wizard", click Next.

Select "Install the hardware that I manually select from a list (Advanced)" and click Next.

Scroll down and select "Network adapters" and click Next.

Select under Manufacturer "Microsoft" and then under Network Adapter "Microsoft KM-TEST Loopback Adapter" or "Microsoft Loopback Adapter" and click Next.

Click Next

Click Finish

Click the Windows Search button and type in "Network Connections".

Run the progam that appears at the top of the search list.

Locate the "Microsoft KM-TEST Loopback Adapter" or "Microsoft Loopback Adapter" and open it.

Click "Properties"

Click "Internet Protocol Version 4 (TCP/IPv4) and then click Properties, or double click it."

Google "What is my IP" to get your public IP address

Enter your public IP address. The rest of the fields shuld be as shown below:

Press Ok to close all the network windows.

Right click and Enable the new adapter

Troubleshooting and Testing Loopback

If your router fails loopback, you can only run a viewer on  the server, even with the driver forcing loopback to work. Without loopback, getting the other PC's on your network to work requires hacks such as a change to the hosts file, and the use of a dynamic DNS system, which is beyond the scope of this article.

There is a built-in web server in Opensim we can use as a diagnostic. To test this driver, run the software and click [Start]. Wait for Opensimulator to boot up.

Now open a web browser and type in "" and it should show a web page. This is just a simple test of the local loopback to Opensim that is found in all PC's, and it must work if Opensim is working and your Windows firewall allows it.

The real test is to use http:// Public Ip and port 8002. You can get this IP address from That is also a good place to test your Port Forwards or uPNP settings.

My results:

    My PC (and yours) is localhost, so this should always work: http://localhost:8002

    Let us assume your Public IP is   So should work.  If it works, your loopback is fine.  If not, the loopback adapter is not running or is misconfigured.


If the "Public IP:Public Port" test fails, your loopback adapter is not working, or the Windows firewall is blocking port 8002, or Opensim is not running. The port can be changed in the advanced settings, so I would double check that the Public Port setting is set for 8002:

Sometimes the adapter/driver  just does not start by itself. You can right click the Network Icon and select "Repair".

Lastly, go check the settings in your adapter for TCP/IP Version 4 and make sure your IP address there is set to the PUBLIC IP address as seen by

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