[C#] weirdness logging IP

I have a function that writes entries to a logfile,

Code:

    protected void Logging(string item1, string item2, string item3)
    { 
        StreamWriter sw = new StreamWriter(Server.MapPath("~\\logs\\RequestLog.txt"),true);
        sw.WriteLine(DateTime.UtcNow.ToLocalTime() + "\t" + item1 + "\t" + item2 + "\t" + item3);
        sw.Flush();
        sw.Close();
    }

I do the IP address lookup like:

Code:

        string ipAddress = HttpContext.Current.Request.ServerVariables["HTTP_X_FORWARDED_FOR"];
        if (ipAddress == null)
        {
            ipAddress = HttpContext.Current.Request.ServerVariables["REMOTE_ADDR"];
        }

the logging function is called like this:

Code:

Logging(Request.QueryString["action"],Request.QueryString["userid"],ipAddress)

No the weird part... some IP addresses are logged as 'unknown', others in a format like this 'xxx.xxx.xxx.xxx, xxx.xxx.xxx.xxx' comma separated.

First, how come some entries are listed as 'unknown', every request should be made by a IP, isn't?
Second, Why some entries contain 2 IP addresses, comma separated?

 

OK, i have found a explanation for the comma separated IP addresses listed, eg: http://en.wikipedia.org/wiki/X-Forwarded-For. Seems the last IP is the IP of the client connecting.

I think modifying the code like this should work and always pick the last IP listed, am i right?

Code:

        string ipAddress = HttpContext.Current.Request.ServerVariables["HTTP_X_FORWARDED_FOR"];
        if (ipAddress == null)
        {
            ipAddress = HttpContext.Current.Request.ServerVariables["REMOTE_ADDR"];
        }
        else {
            string[] elements = ipAddress.Split(',');
            foreach (string element in elements)
            {
                ipAddress = element.Trim();
            }
        }

 

Or maybe better...

Code:

        string ipAddress = HttpContext.Current.Request.ServerVariables["HTTP_X_FORWARDED_FOR"];
        if (ipAddress != null)
        {
            if (ipAddress.IndexOf(',',0) != -1)
            {
                string[] elements = ipAddress.Split(',');
                foreach (string element in elements)
                {
                    ipAddress = element.Trim();
                }
            }
        }
        else
        {
            ipAddress = HttpContext.Current.Request.ServerVariables["REMOTE_ADDR"];
        }