filterContext.HttpContext.Request.UserHostAddress

 private string GetClientIP(HttpActionContext actionContext)

         {

             if (actionContext.Request.Properties.ContainsKey("MS_HttpContext"))

             {

                 return ((HttpContextWrapper)actionContext.Request.Properties["MS_HttpContext"]).Request.UserHostAddress;

             }

             if (actionContext.Request.Properties.ContainsKey(RemoteEndpointMessageProperty.Name))

             {

                 RemoteEndpointMessageProperty prop;

                 prop = (RemoteEndpointMessageProperty)actionContext.Request.Properties[RemoteEndpointMessageProperty.Name];

                 return prop.Address;

             }

             return null;

         }