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要想透过代理服务器取得客户端的真实IP地址,就要使用 Request.ServerVariables("HTTP_X_FORWARDED_FOR") 来读取。不过要注意的事,并不是每个代理服务器都能用 Request.ServerVariables("HTTP_X_FORWARDED_FOR") 来读取客户端的真实 IP,有些用此方法读取到的仍然是代理服务器的IP。还有一点需要注意的是:如果客户端没有通过代理服务器来访问,那么用 Request.ServerVariables ("HTTP_X_FORWARDED_FOR") 取到的值将是空的。因此,如果要在程序中使用此方法,可以这样处理: 
    ...... 
    userip = Request.ServerVariables("HTTP_X_FORWARDED_FOR") 
    If userip = "" Then userip = Request.ServerVariables("REMOTE_ADDR") 
    ......    
    即:如果客户端通过代理服务器,则取 HTTP_X_FORWARDED_FOR 的值,如果没通过代理服务器,就取 REMOTE_ADDR 的值。    
    '通用函数:如果不能取客户端真实IP,就会取客户端的代理IP 
    Private Function getIP() 
    Dim strIPAddr 
    If Request.ServerVariables("HTTP_X_FORWARDED_FOR") = "" OR InStr(Request.ServerVariables("HTTP_X_FORWARDED_FOR"), "unknown") > 0 Then 
    strIPAddr = Request.ServerVariables("REMOTE_ADDR") 
    ElseIf InStr(Request.ServerVariables("HTTP_X_FORWARDED_FOR"), ",") > 0 Then 
    strIPAddr = Mid(Request.ServerVariables("HTTP_X_FORWARDED_FOR"), 1, InStr(Request.ServerVariables("HTTP_X_FORWARDED_FOR"), ",")-1) 
    ElseIf InStr(Request.ServerVariables("HTTP_X_FORWARDED_FOR"), ";") > 0 Then 
    strIPAddr = Mid(Request.ServerVariables("HTTP_X_FORWARDED_FOR"), 1, InStr(Request.ServerVariables("HTTP_X_FORWARDED_FOR"), ";")-1) 
    Else 
    strIPAddr = Request.ServerVariables("HTTP_X_FORWARDED_FOR") 
    End If 
    getIP = Trim(Mid(strIPAddr, 1, 30)) 
    End Function 
   
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