https://blog.csdn.net/chuntian1983/article/details/2233191
https://www.cnblogs.com/00OO/archive/2011/04/30/2033633.html
https://www.cnblogs.com/kingboy/archive/2013/08/18/3266255.html
https://www.cnblogs.com/davytitan/archive/2012/09/13/2682852.html

string?result?=?HttpContext.Current.Request.ServerVariables["HTTP_X_FORWARDED_FOR"];
???if?(null?==?result?||?result?==?String.Empty)
???{
????result?=?HttpContext.Current.Request.ServerVariables["REMOTE_ADDR"];
???}
???if?(null?==?result?||?result?==?String.Empty)
???{
????result?=?HttpContext.Current.Request.UserHostAddress;
???}
???return?result;