内容提示：在多服务器资源网站的项目中，经常需要自动根据用户的IP选择最优先的服务器资源进行特定的指向服务，这就需要对客户IP是否存在网段的判断技术，下面整理两个版本的例子，供大家参考。

[C#.net版]如何判断某一个IP是否在一个ＩＰ段里边

/// <summary>
/// 分割IP
/// </summary>
/// <param name="ipAddress">IP地址</param>
/// <returns></returns>
private long getIpNum(String ipAddress)
{
 String[] ip = ipAddress.Split(new char[] { '.' });
 long a = int.Parse(ip[0]);
 long b = int.Parse(ip[1]);
 long c = int.Parse(ip[2]);
 long d = int.Parse(ip[3]);

return a * 256 * 256 * 256 + b * 256 * 256 + c * 256 + d;
}

/// 判断客户端的IP是否在某个ip段中

/// <param name="clientIp">客户端的IP</param>
/// <param name="begin">开始IP</param>
/// <param name="end">结束IP</param>
/// <returns></returns>
private bool isInner(long clientIp, long begin, long end)
{
 return (clientIp >= begin) && (clientIp <= end);
}

///调用方法

long ip = getIpNum("59.162.200.35");
long start_ip = getIpNum("59.162.200.0");
long end_ip = getIpNum("59.162.201.255");

if (isInner(ip, start_ip, end_ip))
{
 Response.Write("是");
}
else
{
 Response.Write("不是");
}

[Java版]判断一个IP是否在指定网段中

/** 
* 判断ip是否在指定网段中 
* @author dh 
* @param iparea 
* @param ip 
* @return boolean 
*/ 
public static boolean ipIsInNet(String iparea, String ip) {  
 if (iparea == null)  
  throw new NullPointerException("IP段不能为空！");  
 if (ip == null)  
　　throw new NullPointerException("IP不能为空！");  
 iparea = iparea.trim();  
 ip = ip.trim();  
 final String REGX_IP = "((25[0-5]|2[0-4]\\d|1\\d{2}|[1-9]\\d|\\d)\\.){3}(25[0-5]|2[0-4]\\d|1\\d{2}|[1-9]\\d|\\d)";  
 final String REGX_IPB = REGX_IP + "\\-" + REGX_IP;  
 if (!iparea.matches(REGX_IPB) || !ip.matches(REGX_IP))  
　　return false;  
 int idx = iparea.indexOf('-');  
 String[] sips = iparea.substring(0, idx).split("\\.");  
 String[] sipe = iparea.substring(idx + 1).split("\\.");  
 String[] sipt = ip.split("\\.");  
 long ips = 0L, ipe = 0L, ipt = 0L;  
 for (int i = 0; i < 4; ++i) {  
  ips = ips << 8 | Integer.parseInt(sips[i]);  
  ipe = ipe << 8 | Integer.parseInt(sipe[i]);  
  ipt = ipt << 8 | Integer.parseInt(sipt[i]);  
 }  
 if (ips > ipe) {  
  long t = ips;  
  ips = ipe;  
  ipe = t;  
 }  
 return ips <= ipt && ipt <= ipe;  
}