>>Not sure what you mean by 'primary' address. On my machine your code (or, at least, my Linq version of it) returns 4 IP4 addresses, two for wireless and two for Ethernet. Don't see any way to distinguish which one you might be looking for.....
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>From the load balancing environment, several Web servers will respond to the same domain but will hit one single SQL Server database. For each hit, I need to know which Web server responded to the request. Before, without a load balancing, I didn't have a need to add a Hit.IPServer field. I only add a Hit.IP which indicates the IP of the user. But, now, I need the IP of the server. So far, it returns the proper IP. But, then again, if you say the condition was met for 4 addresses on your PC, then that condition does not resolve with accuracy what I am looking for.
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>Do you have any idea on how to improve based on this additional information?

Can you not use System.Environment.MachineName instead?
Don't know much about Web Farms but if DNS is used then the IP address would not reliably identify a specific machine anyway....