In ASP.NET, how do you acquire a user’s client IP address?

Problem

In ASP.NET, we have Request.UserHostAddress, but this is normally the user’s ISP’s IP address, not the user’s machine IP address who, for example, clicked a link. How can I find out what my true IP address is?

For example, “Last account activity: 4 hours ago from 86.123.127.8” appears in a Stack Overflow user profile, but my workstation IP address is different. What method does Stack Overflow use to obtain this address?

For several purposes, IP addresses are checked in some web systems. Can a person with a specific IP address, for example, only click on 5 download links every 24 hours? Not for an ISP with a large number of clients or Internet users, this IP address should be unique.

Did I get it right?

Asked by Mehdi

Solution #1

You’ll frequently need to know someone’s IP address when they visit your website. While there are various ways to accomplish this in ASP.NET, we’ve found that using the ServerVariables collection’s “HTTP X FORWARDED FOR” is one of the most effective.

Here’s why…

Your visitors may be behind a proxy server or a router, and the usual Request will not work. UserHostAddress solely records the proxy server’s or router’s IP address. When this happens, the user’s IP address is saved in a server variable called “HTTP X FORWARDED FOR.”

So we’ll check “HTTP X FORWARDED FOR” first, and if it’s empty, we’ll simply return ServerVariables(“REMOTE ADDR”).

a number of IP addresses”

C#

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];
        }
    }

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

VB.NET

Public Shared Function GetIPAddress() As String
    Dim context As System.Web.HttpContext = System.Web.HttpContext.Current
    Dim sIPAddress As String = context.Request.ServerVariables("HTTP_X_FORWARDED_FOR")
    If String.IsNullOrEmpty(sIPAddress) Then
        Return context.Request.ServerVariables("REMOTE_ADDR")
    Else
        Dim ipArray As String() = sIPAddress.Split(New [Char]() {","c})
        Return ipArray(0)
    End If
End Function

Answered by mangokun

Solution #2

You can’t do what you’re asking, as others have stated. Perhaps someone can assist you if you detail the problem you’re trying to solve?

E.g.

The traffic is correctly routed to each device. Users browsing from an office environment may find that the address is the same for everyone. Sites that rely on IP addresses for identification face the danger of getting it horribly wrong – the examples you provide are excellent, yet they frequently fail. My workplace, for example, is in the United Kingdom, but my breakout point (where I “look” to be on the internet) is in another nation, where our primary IT facility is located, thus my IP address appears to be outside of the United Kingdom from my office. As a result, I am unable to access UK-only web content (such as the BBC iPlayer). There would be hundreds, if not thousands, of individuals at my organization at any given time.

When writing server code, you never know what IP address the address you see refers to. This is how some users prefer it. Some people purposefully use a proxy or VPN to confuse you.

How are you determining your machine address when you state it’s different from the IP address listed on StackOverflow? If you merely use ipconfig or something like to search locally, I’d expect it to be different for the reasons I mentioned before. Check out whatismyipaddress.com/ to double-check what the rest of the world believes.

This NAT Wikipedia link will provide you some background information.

Answered by Steve

Solution #3

Thanks to Bruno Lopes for the update. If many IP addresses are expected, this approach should be used:

    private string GetUserIP()
    {
        string ipList = Request.ServerVariables["HTTP_X_FORWARDED_FOR"];

        if (!string.IsNullOrEmpty(ipList))
        {
            return ipList.Split(',')[0];
        }

        return Request.ServerVariables["REMOTE_ADDR"];
    }

Answered by algreat

Solution #4

If you look at it this way, c# is pretty straightforward.

string clientIp = (Request.ServerVariables["HTTP_X_FORWARDED_FOR"] ?? 
                   Request.ServerVariables["REMOTE_ADDR"]).Split(',')[0].Trim();

Answered by Juan David Nicholls Cardona

Solution #5

Do you think about the user’s IP address? I’m afraid there’s no method to get the IP address of the network adapter in a Web app. If your user is behind NAT or other stuff, you can’t get the IP either.

Update: While some Web sites, such as rapidshare, use IP to limit users, they do not work well in NAT setups.

Answered by mmx

Post is based on https://stackoverflow.com/questions/735350/how-to-get-a-users-client-ip-address-in-asp-net