接続元のIPアドレスが指定された範囲内かどうかを調べる

private bool IsInSubnet(string networkAddress, string netMask)

{

	IPAddress clientIP = IPAddress.Parse(Request.UserHostAddress);

	IPAddress networkIP = IPAddress.Parse(networkAddress);
	byte[] clientIPInBytes = clientIP.GetAddressBytes();

	string clientIPBits = null;

	foreach(byte b in clientIPInBytes)

	{

		clientIPBits = clientIPBits + Convert.ToString(b,2).PadLeft(8,'0');

	}
	byte[] networkIPInBytes = networkIP.GetAddressBytes();

	string networkIPBits = null;

	foreach(byte b in networkIPInBytes)

	{

		networkIPBits = networkIPBits + Convert.ToString(b,2).PadLeft(8,'0');

	}
	int mask = int.Parse(netMask);

	for(int i = 0; i < mask; i++)

	{

		if(clientIPBits[i] != networkIPBits[i])

		{

			return false;

		}

	}

	

	return true;

}