在启用了IPV6的机器上获取客户端ipv4地址

using System;   
using System.Net;    
using System.Web; 
public class IPNetworking   
{    
    /// <summary>    
    /// 取得客戶端主機 IPv4 地址    
    /// </summary>    
    /// <returns></returns>    
    public static string GetClientIPv4()    
    {    
        string ipv4 = String.Empty; 
        foreach (IPAddress ip in Dns.GetHostAddresses(GetClientIP()))   
        {    
            if (ip.AddressFamily.ToString() == "InterNetwork")    
            {    
                ipv4 = ip.ToString();    
                break;    
            }    
        } 
        if (ipv4 != String.Empty)   
        {    
            return ipv4;    
        } 
        // 原代码使用 Dns.GetHostName 方法取回的是 Server 端资料，非 Client 端。   
        // 改为利用 Dns.GetHostEntry 方法，由获取的 IPv6 位址反查 DNS 记录，    
        // 再逐一判断是否属于 IPv4 协议定，如果是转换为 IPv4 地址。    
        foreach (IPAddress ip in Dns.GetHostEntry(GetClientIP()).AddressList)    
        //foreach (IPAddress ip in Dns.GetHostAddresses(Dns.GetHostName()))    
        {    
            if (ip.AddressFamily.ToString() == "InterNetwork")    
            {    
                ipv4 = ip.ToString();    
                break;    
            }    
        } 
        return ipv4;   
    } 
    /// <summary>   
    /// 取得客戶端主机地址    
    /// </summary>    
    public static string GetClientIP()    
    {    
        if (null == HttpContext.Current.Request.ServerVariables["HTTP_VIA"])    
        {    
            return HttpContext.Current.Request.ServerVariables["REMOTE_ADDR"];    
        }    
        else    
        {    
            return HttpContext.Current.Request.ServerVariables["HTTP_X_FORWARDED_FOR"];    
        }    
    }    
}