工具类：

using System;

namespace CommonUtils
{
    public static class ClientIpUtil
    {
        public static string GetClientIpMvc()
        {
            string userIP = "127.0.0.1";

            try
            {
                if (System.Web.HttpContext.Current == null
                 || System.Web.HttpContext.Current.Request == null
                 || System.Web.HttpContext.Current.Request.ServerVariables == null)
                {
                    return "";
                }

                string CustomerIP = "";

                //CDN加速后取到的IP simone 090805
                CustomerIP = System.Web.HttpContext.Current.Request.Headers["Cdn-Src-Ip"];
                if (!string.IsNullOrEmpty(CustomerIP))
                {
                    return CustomerIP;
                }

                CustomerIP = System.Web.HttpContext.Current.Request.ServerVariables["HTTP_X_FORWARDED_FOR"];

                if (!String.IsNullOrEmpty(CustomerIP))
                {
                    return CustomerIP;
                }
                if (System.Web.HttpContext.Current.Request.ServerVariables["HTTP_VIA"] != null)
                {
                    CustomerIP = System.Web.HttpContext.Current.Request.ServerVariables["HTTP_X_FORWARDED_FOR"];

                    if (CustomerIP == null)
                    {
                        CustomerIP = System.Web.HttpContext.Current.Request.ServerVariables["REMOTE_ADDR"];
                    }
                }
                else
                {
                    CustomerIP = System.Web.HttpContext.Current.Request.ServerVariables["REMOTE_ADDR"];
                }

                if (string.Compare(CustomerIP, "unknown", true) == 0 || String.IsNullOrEmpty(CustomerIP))
                {
                    return System.Web.HttpContext.Current.Request.UserHostAddress;
                }

                if (!CustomerIP.Contains("."))
                    CustomerIP = "127.0.0.1";

                return CustomerIP;
            }
            catch { }


            return userIP;
        }
    }
}

使用：

string ip = ClientIpUtil.GetClientIpMvc();