How to retrieve client IP address in ASP.NET Core 3.1 API

[SwiftCoder15]

I’m working on a project with ASP.NET Core 3.1 Web API and I need to capture the client’s IP address for logging purposes. I’ve tried several approaches but I’m not getting the correct results. Sometimes I get localhost or internal server addresses instead of the actual client IP.

I’m particularly confused about how to handle situations where the application is behind a proxy or load balancer. Can someone show me the proper way to extract the real client IP address from the HTTP request?

Here’s a basic example of what I’m trying to achieve:

[ApiController]
[Route("api/[controller]")]
public class ClientController : ControllerBase
{
    [HttpGet("info")]
    public IActionResult GetClientInfo()
    {
        // Need to get client IP here
        var clientIP = "???"; // How to get this?
        return Ok(new { ClientAddress = clientIP });
    }
}

Any help would be appreciated!

[Hazel_27Yoga]

To retrieve the client’s actual IP address in ASP.NET Core 3.1, you should utilize HttpContext.Connection.RemoteIpAddress, with due caution regarding proxy configurations. In situations where your application may be using a proxy or load balancer, it’s essential to first check the X-Forwarded-For header, as this typically contains the true client IP. Here’s an example of how to implement it:

public string GetClientIP()
{
    var ipAddress = HttpContext.Connection.RemoteIpAddress;
    
    // Inspect forwarded IPs
    if (Request.Headers.ContainsKey("X-Forwarded-For"))
    {
        var forwardedIps = Request.Headers["X-Forwarded-For"].ToString();
        if (!string.IsNullOrEmpty(forwardedIps))
        {
            return forwardedIps.Split(',')[0].Trim();
        }
    }
    
    return ipAddress?.ToString() ?? "Unknown";
}

Ensure that the forwarded headers middleware is configured in your Startup.cs before UseRouting:

app.UseForwardedHeaders(new ForwardedHeadersOptions
{
    ForwardedHeaders = ForwardedHeaders.XForwardedFor | ForwardedHeaders.XForwardedProto
});

This will help avoid getting localhost addresses when your application is hosted behind proxies.

[Claire29]

also check Request.HttpContext.Connection.RemoteIpAddress?.ToString(). if behind nginx or cloudflare, you should look at X-Real-IP header. cloudflare usually uses CF-Connecting-IP, so you might wanna check that based on your proxy config.

[DancingBird]

Had this exact problem last year with Azure behind Application Gateway. Most solutions miss the key part - you’ve got to configure forwarded headers correctly for your network setup. Define known networks and proxies or you’ll have security issues. In Program.cs or Startup.cs: csharp services.Configure<ForwardedHeadersOptions>(options => { options.ForwardedHeaders = ForwardedHeaders.XForwardedFor | ForwardedHeaders.XForwardedProto; options.KnownNetworks.Clear(); options.KnownProxies.Clear(); }); For your controller, make a helper method that checks multiple headers in order: csharp private string GetRealClientIP() { return Request.Headers["CF-Connecting-IP"].FirstOrDefault() ?? Request.Headers["X-Forwarded-For"].FirstOrDefault()?.Split(',')[0] ?? Request.Headers["X-Real-IP"].FirstOrDefault() ?? HttpContext.Connection.RemoteIpAddress?.ToString() ?? "unknown"; } This works reliably across different setups - I’ve used it with AWS ALB and Cloudflare without issues.