How to Get the True Client IP Address in ASP.NET?

Accurate Client IP Address Retrieval in ASP.NET Applications

Determining the user's actual IP address is vital for many ASP.NET applications, including user identification and traffic management. While Request.UserHostAddress provides an IP address, it often represents the proxy server or load balancer, not the end-user's device.

Leveraging HTTP_X_FORWARDED_FOR

The solution lies in using the HTTP_X_FORWARDED_FOR server variable. This variable stores the original client IP address when requests traverse proxy servers or network devices. Prioritizing HTTP_X_FORWARDED_FOR ensures retrieval of the accurate IP address.

C# and VB.NET Code Examples

The following code snippets demonstrate how to implement this solution in both C# and VB.NET:

protected string GetIPAddress()
{
    System.Web.HttpContext context = System.Web.HttpContext.Current;
    string ipAddress = context.Request.ServerVariables["HTTP_X_FORWARDED_FOR"];

    if (!string.IsNullOrEmpty(ipAddress))
    {
        string[] addresses = ipAddress.Split(',');
        if (addresses.Length > 0)
        {
            return addresses[0].Trim(); //Added Trim to remove whitespace
        }
    }

    return context.Request.ServerVariables["REMOTE_ADDR"];
}

Public Shared Function GetIPAddress() As String
    Dim context As System.Web.HttpContext = System.Web.HttpContext.Current
    Dim ipAddress As String = context.Request.ServerVariables("HTTP_X_FORWARDED_FOR")

    If Not String.IsNullOrEmpty(ipAddress) Then
        Dim addresses As String() = ipAddress.Split(","c)
        If addresses.Length > 0 Then
            Return addresses(0).Trim() 'Added Trim to remove whitespace
        End If
    End If

    Return context.Request.ServerVariables("REMOTE_ADDR")
End Function

These functions first check for HTTP_X_FORWARDED_FOR. If present, it extracts the first IP address from the comma-separated list. If not found, it falls back to REMOTE_ADDR. A Trim() function has been added to remove any leading or trailing whitespace from the IP address string for better reliability. This method significantly improves the accuracy of obtaining the true client IP address, bolstering application security and functionality.

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