給定 IP 地址和子網掩碼，如何計算 CIDR？

Question

好吧，我似乎無法弄清楚：鑒於以下內容：

IP address = 192.168.1.0
Subnetmask = 255.255.255.240

使用 c#，如何計算 CIDR 表示法192.168.1.0/28 ？ 有沒有簡單的方法來實現這一目標？ 我錯過了什么嗎？

謝謝！

Answer 1

256 - 240 = 16 = 2**4, 32 - 4 = 28

這不是一個真正的 C# 問題。

要從 IP 和掩碼獲取網絡地址，您可以按字節應用and到 IP 和掩碼。 您可以使用IPAddress.Parse()和IPAddress.GetAddressBytes()從字符串中獲取字節。

Answer 2

我不得不做同樣的事情，沒有新信息，但是這個片段可能會派上用場，供下一個人尋找在 C# 中執行此操作的方法。 請注意，此方法僅計算連續 1 的數量，並留給您將其附加到 IP 的工作。

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;
    }
}

Answer 3

把事情簡單化！

這僅適用於 IPv4 ，但由於 IPv6 只支持像/64這樣的 CIDR 在fe80::1ff:fe23:4567:890a/64計算中是不必要的。

IPv4 網絡掩碼所需的一切：

int cidr = Convert.ToString(mask.Address, 2).Count( o => o == '1'); 

基於給定示例的解釋：

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'); 

Answer 4

我沒有它作為 C# 代碼，但這是 VB 中的答案。 應該不難轉換。

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

Answer 5

我的解決方案，首先解析為IPAddress：

var Subnetmask = "255.255.255.240";
IPAddress ip = IPAddress.Parse(Subnetmask);

然后，檢查掩碼 ip 中設置位的計數：

var intAddress = (int)IPAddress.Address;
Console.WriteLine(NumberOfSetBits(intAddress)); //28

函數（來自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;
}

Answer 6

我知道這有點晚了，但是我將上面 dbasnett 的答案VB.NET 代碼轉換為 C#（感謝Telerik Code Converter ）並將其放在 .NET Fiddle 中，並在下面包含了我的轉換：

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;
}

Answer 7

請參閱從網絡掩碼獲取 CIDR

用法：

var cidrnetmask = MaskToCIDR(IPAddress.Parse("255.0.0.0").GetAddressBytes());

這適用於 IPv4。 為了支持 IPv6，可以擴展字節數，但希望沒有人會嘗試為 IPv6 使用舊式網絡掩碼 :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;
}