How Can I Reliably Retrieve a User's Real IP Address in ASP.NET?

Obtaining the True User IP Address in ASP.NET Applications

In ASP.NET, directly using Request.UserHostAddress often yields the IP address of an intermediary server (like a proxy or load balancer), not the actual client's IP. This is problematic for applications needing accurate IP addresses for security or analytics.

A more reliable method involves checking the HTTP_X_FORWARDED_FOR server variable. This variable, when present, contains the original client IP address, especially in scenarios with proxies or load balancers. However, it might list multiple IPs.

The following code snippets demonstrate how to extract the user's IP address effectively:

C#

<code class="language-csharp">protected string GetClientIpAddress()
{
    var context = System.Web.HttpContext.Current;
    string ipAddress = context.Request.ServerVariables["HTTP_X_FORWARDED_FOR"];

    if (!string.IsNullOrWhiteSpace(ipAddress))
    {
        return ipAddress.Split(',')[0].Trim();
    }

    return context.Request.ServerVariables["REMOTE_ADDR"];
}</code>

VB.NET

<code class="language-vb.net">Public Shared Function GetClientIpAddress() 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.IsNullOrWhiteSpace(ipAddress) Then
        Return ipAddress.Split(","c)(0).Trim()
    End If

    Return context.Request.ServerVariables("REMOTE_ADDR")
End Function</code>

These functions prioritize HTTP_X_FORWARDED_FOR, extracting the first IP address. If this variable is missing, they fall back to REMOTE_ADDR. This approach improves the accuracy of IP address retrieval in your ASP.NET applications, leading to more precise user identification and better IP-based controls.

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