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Load balancing is the idea of two servers sharing a single address - in this case a sort of virtual address/MAC - requests made to the IIS server can be handled by either server - they switch back and forth. This helps balance the load in a simple manner. To determine which server is actually serving up the webpage you can modify the pages of both servers to indicate their IP address, you can also change the background color within the body tag.
<body bgcolor=red text=black> etc..
In normal situations the content would be identical on both servers.