或許可朝透過javascript去存取client ip思考
https://stackoverflow.com/questions/391979/how-to-get-clients-ip-address-using-javascript

最近網路上找的 剛好用到專案上
IIS
ASP.NET Web Forms C#

 using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

public partial class _Default : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        string vClientIP = GetIPAddress();//取得ClientIP 
        Response.Write(vClientIP);

    }

    //Get Ip Address
    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"];
    }
}

我這邊有一些取 ip 的方法給你參考，看有沒有你需要的

/// <summary>
/// 取得本機 IP Address
/// </summary>
/// <returns></returns>
public static List<string> GetHostIPAddress()
{
	List<string> lstIPAddress = new List<string>();
	IPHostEntry IpEntry = Dns.GetHostEntry(Dns.GetHostName());
	foreach (IPAddress ipa in IpEntry.AddressList)
	{
		if (ipa.AddressFamily == AddressFamily.InterNetwork)
			lstIPAddress.Add(ipa.ToString());
	}
	return lstIPAddress;
}

/// <summary>
/// 取得遠端呼叫者ip
/// </summary>
/// <returns></returns>
public string GetClientIP()
{
	string ClientIP = "";
	if (Request.ServerVariables["HTTP_VIA"] == null)
	{
		ClientIP = Request.ServerVariables["REMOTE_ADDR"].ToString();
	}
	else
	{
		ClientIP = Request.ServerVariables["HTTP_X_FORWARDED_FOR"].ToString();
	}
	ClientIP = ClientIP.Replace("::1", "127.0.0.1");
	return ClientIP;
}

/// <summary>
/// 取得外網 IP Address
/// </summary>
/// <returns></returns>
public static string GetExtranetIPAddress()
{
	HttpWebRequest request = HttpWebRequest.Create("http://www.whatismyip.com.tw") as HttpWebRequest;
	request.Method = "GET";
	request.ContentType = "application/x-www-form-urlencoded";
	request.UserAgent = "Mozilla/5.0";
	string ip = string.Empty;
	WebResponse response = request.GetResponse();
	using (StreamReader reader = new StreamReader(response.GetResponseStream()))
	{
		string result = reader.ReadToEnd();
		string pattern = @"\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}";
		ip = Regex.Match(result, pattern).ToString();
	}
	return ip;
}