服务端：
//方法一HttpContext.Current.Request.UserHostAddress; //方法二HttpContext.Current.Request.ServerVariables["REMOTE_ADDR"];//方法三string strHostName = System.Net.Dns.GetHostName();string clientIPAddress = System.Net.Dns.GetHostAddresses(strHostName).GetValue(0).ToString();//方法四（无视代理）HttpContext.Current.Request.ServerVariables["HTTP_X_FORWARDED_FOR"];
客户端：
//方法五var ip = '<!--#echo var="REMOTE_ADDR"-->';alert("Your IP address is "+ip);//方法六（无视代理）function GetLocalIPAddress() 
{ 
var obj = null; var rslt = ""; try 
{ 
obj = new ActiveXObject("rcbdyctl.Setting"); rslt = obj.GetIPAddress; obj = null; 
} catch(e) { // } return rslt; 
} 来自印度的MCT Maulik Patel提供了一种服务端的解决方案，很好：
if(Context.Request.ServerVariables["HTTP_VIA"]!=null) // using proxy{ ip=Context.Request.ServerVariables["HTTP_X_FORWARDED_FOR"].ToString(); // Return real client IP.}else// not using proxy or can't get the Client IP{ ip=Context.Request.ServerVariables["REMOTE_ADDR"].ToString(); //While it can't get the Client IP, it will return proxy IP.}
备注：
1. 有些代理是不会发给我们真实IP地址的
2. 有些客户端会因为“header_access deny”的安全设置而不发给我们IP
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