好吧我似乎无法弄明白：给出以下内容：
IP address = 192.168.1.0
Subnetmask = 255.255.255.240
使用c＃，如何计算CIDR表示法192.168.1.0/28？有没有一种简单的方法来实现这一目标？我错过了什么吗？
谢谢！
答案 0 :(得分：6)
256 - 240 = 16 = 2**4, 32 - 4 = 28
这不是一个真正的C＃问题。
要从IP和掩码中获取网络地址，您可以将字节and应用于IP和掩码。您可以使用IPAddress.Parse()和IPAddress.GetAddressBytes()从字符串中获取字节。
答案 1 :(得分：3)
我必须做同样的事情，没有新的信息，但这个片段可能会派上用场，以便下一个人在C＃中寻找一种方法。 请注意，此方法仅计算连续1的数量，并让您将其附加到IP。
public class IPAddressHelper
{
public static UInt32 SubnetToCIDR(string subnetStr)
{
IPAddress subnetAddress = IPAddress.Parse(subnetStr);
byte[] ipParts = subnetAddress.GetAddressBytes();
UInt32 subnet = 16777216 * Convert.ToUInt32(ipParts[0]) + 65536 * Convert.ToUInt32(ipParts[1]) + 256 * Convert.ToUInt32(ipParts[2]) + Convert.ToUInt32(ipParts[3]);
UInt32 mask = 0x80000000;
UInt32 subnetConsecutiveOnes = 0;
for (int i = 0; i < 32; i++)
{
if (!(mask & subnet).Equals(mask)) break;
subnetConsecutiveOnes++;
mask = mask >> 1;
}
return subnetConsecutiveOnes;
}
}
答案 2 :(得分：2)
我没有它作为C＃代码，但这是VB中的答案。不应该难以转换。
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim someIP As Net.IPAddress = Net.IPAddress.Parse("192.168.1.10")
Dim someMASK As Net.IPAddress = Net.IPAddress.Parse("255.255.255.240")
Dim ipL As Long = IPtoLong(someIP)
Dim maskL As Long = IPtoLong(someMASK)
'Convert Mask to CIDR(1-30)
Dim oneBit As Long = &H80000000L
Dim CIDR As Integer = 0
For x As Integer = 31 To 0 Step -1
If (maskL And oneBit) = oneBit Then CIDR += 1 Else Exit For
oneBit = oneBit >> 1
Next
Dim answer As String = LongToIp(ipL And maskL) & " /" & CIDR.ToString
End Sub
Public Function IPtoLong(ByVal theIP As Net.IPAddress) As Long 'convert IP to number
Dim IPb() As Byte = theIP.GetAddressBytes 'get the octets
Dim addr As Long 'accumulator for address
For x As Integer = 0 To 3
addr = addr Or (CLng(IPb(x)) << (3 - x) * 8)
Next
Return addr
End Function
Public Function LongToIp(ByVal theIP As Long) As String 'convert number back to IP
Dim IPb(3) As Byte '4 octets
Dim addr As String = "" 'accumulator for address
Dim mask8 As Long = MaskFromCidr(8) 'create eight bit mask
For x = 0 To 3 'get the octets
IPb(x) = CByte((theIP And mask8) >> ((3 - x) * 8))
mask8 = mask8 >> 8
addr &= IPb(x).ToString & "." 'add current octet to string
Next
Return addr.TrimEnd("."c)
End Function
Private Function MaskFromCidr(ByVal CIDR As Integer) As Long
MaskFromCidr = CLng(2 ^ ((32 - CIDR)) - 1) Xor 4294967295L
End Function
答案 3 :(得分：1)
保持简单！
这仅适用于IPv4 ，但是由于IPv6仅支持CIDR（例如/64中的fe80::1ff:fe23:4567:890a/64），因此不需要像这样。
所有需要的IPv4网络掩码：
int cidr = Convert.ToString(mask.Address, 2).Count( o => o == '1');
基于给定示例的说明：
IPAddress mask = new IPAddress(new byte[] { 255, 255, 255, 240 });
// maskBinAsString = 11110000111101001111111111111111
string maskBinAsString = Convert.ToString(mask.Address, 2);
// cidr = 28
int cidr = Convert.ToString(mask.Address, 2).Count( o=> o == '1');
答案 4 :(得分：0)
用法：
var cidrnetmask = MaskToCIDR(IPAddress.Parse("255.0.0.0").GetAddressBytes());
这适用于IPv4。为了支持IPv6，可以扩展字节数，但希望没有人会尝试使用旧式网络掩码用于IPv6：o）
方法：
static int MaskToCIDR(byte[] bytes)
{
var b0 = bytes[0];
var b1 = bytes[1];
var b2 = bytes[2];
var b3 = bytes[3];
return
b3 != 0 ? (
(b3 & 0x01) != 0 ? 32 :
(b3 & 0x02) != 0 ? 31 :
(b3 & 0x04) != 0 ? 30 :
(b3 & 0x08) != 0 ? 29 :
(b3 & 0x10) != 0 ? 28 :
(b3 & 0x20) != 0 ? 27 :
(b3 & 0x40) != 0 ? 26 :
25 ) :
b2 != 0 ? (
(b2 & 0x01) != 0 ? 24 :
(b2 & 0x02) != 0 ? 23 :
(b2 & 0x04) != 0 ? 22 :
(b2 & 0x08) != 0 ? 21 :
(b2 & 0x10) != 0 ? 20 :
(b2 & 0x20) != 0 ? 19 :
(b2 & 0x40) != 0 ? 18 :
17 ) :
b1 != 0 ? (
(b1 & 0x01) != 0 ? 16 :
(b1 & 0x02) != 0 ? 15 :
(b1 & 0x04) != 0 ? 14 :
(b1 & 0x08) != 0 ? 13 :
(b1 & 0x10) != 0 ? 12 :
(b1 & 0x20) != 0 ? 11 :
(b1 & 0x40) != 0 ? 10 :
9 ) :
b0 != 0 ? (
(b0 & 0x01) != 0 ? 8 :
(b0 & 0x02) != 0 ? 7 :
(b0 & 0x04) != 0 ? 6 :
(b0 & 0x08) != 0 ? 5 :
(b0 & 0x10) != 0 ? 4 :
(b0 & 0x20) != 0 ? 3 :
(b0 & 0x40) != 0 ? 2 :
1 ) :
0;
}
答案 5 :(得分：0)
我的解决方案，首先解析为IPAddress：
var Subnetmask = "255.255.255.240";
IPAddress ip = IPAddress.Parse(Subnetmask);
然后，检查掩码ip中的设置位数：
var intAddress = (int)IPAddress.Address;
Console.WriteLine(NumberOfSetBits(intAddress)); //28
该功能（来自https://stackoverflow.com/a/12175897/1271037）：
int NumberOfSetBits(int i)
{
i = i - ((i >> 1) & 0x55555555);
i = (i & 0x33333333) + ((i >> 2) & 0x33333333);
return (((i + (i >> 4)) & 0x0F0F0F0F) * 0x01010101) >> 24;
}
答案 6 :(得分：0)
我知道已经有点晚了，但是我花了一些时间将上面的dbasnett's answer VB.NET代码转换为C＃（感谢Telerik Code Converter）并将其放入.NET提琴{{3} }，并在下面添加了我的转化
public static void Main()
{
System.Net.IPAddress someIP = System.Net.IPAddress.Parse("192.168.1.23");
System.Net.IPAddress someMASK = System.Net.IPAddress.Parse("255.255.255.128");
long ipL = IPtoLong(someIP);
long maskL = IPtoLong(someMASK);
// Convert Mask to CIDR(1-30)
long oneBit = 0x80000000L;
int CIDR = 0;
for (int x = 31; x >= 0; x += -1)
{
if ((maskL & oneBit) == oneBit)
CIDR += 1;
else
break;
oneBit = oneBit >> 1;
}
string answer = LongToIp(ipL & maskL) + "/" + CIDR.ToString();
Console.Out.WriteLine("woah woah we woah " + answer);
}
public static long IPtoLong(System.Net.IPAddress theIP) // convert IP to number
{
byte[] IPb = theIP.GetAddressBytes(); // get the octets
long addr = 0; // accumulator for address
for (int x = 0; x <= 3; x++) {
addr |= (System.Convert.ToInt64(IPb[x]) << (3 - x) * 8);
}
return addr;
}
public static string LongToIp(long theIP) // convert number back to IP
{
byte[] IPb = new byte[4]; // 4 octets
string addr = ""; // accumulator for address
long mask8 = MaskFromCidr(8); // create eight bit mask
for (var x = 0; x <= 3; x++) // get the octets
{
IPb[x] = System.Convert.ToByte((theIP & mask8) >> ((3 - x) * 8));
mask8 = mask8 >> 8;
addr += IPb[x].ToString() + "."; // add current octet to string
}
return addr.TrimEnd('.');
}
private static long MaskFromCidr(int CIDR)
{
return System.Convert.ToInt64(Math.Pow(2, ((32 - CIDR))) - 1) ^ 4294967295L;
}