>>>>>As you correctly indicated, I am getting "::1" for IP when running on my local Web Site. Do I understand that when I deploy the app to the customer web site (and they will hit it not from local web site), I will see valid IPs?
>>>>
>>>>You will see a valid IP if your site responds to the Internet.
>>>>
>>>>Note that you might get multiple occurences of the same IP for various users, assuming those users are from the same company going out through the same proxy.
>>>
>>>Thank you (and Viv). For me it is important to log the IP of a user who submits within several seconds. Basically I am troubleshooting the following issue. Users submits duplicate orders by Submitting and then clicking on Back and Submitting again. They claim that they don't do it. And the only way I can prove to them (and to myself) is by logging every Submit with the IP and order number. So two submits within seconds with the consecutive order numbers and the same "IP" will show the trend.
>>
>>I agree with Michel and Viv - disable the submit button as soon as they submit the order. If they hit the back button the page is normally pulled from the browser cache so the button will still be disabled. Another approach is to embed a unique # in a hidden field in the page that gets stored with the order. Before saving use this value to check to see if it's been previously submitted. Or, if you don't want to do that, use the customer + invoice total + invoice date as a key - when they submit check to see if an invoice for the same customer/amount/date exists. If it does, prompt them to confirm before sving.
>
>Thank you. I am taking notes of all suggestions and may implement some or all of them in the next update.

After they submit the page, do you redirect them to a new page, or leave them on the page they just submitted? If you leave them on the page, a refresh will also cause it to be resubmitted. Redirecting them to a different results page can correct this. See http://en.wikipedia.org/wiki/Post/Redirect/Get.

You can also try setting the cacheability of the page to no-cache and set it to expired (expired date in the past). These are available from various functions on the Response.Cache object. See http://msdn.microsoft.com/en-us/library/system.web.httpcachepolicy%28v=vs.110%29.aspx.