I have a subnet in the format 10.132.0.0/20 and an IP address from the ASP.Net request object.
Is there a .NET framework function to check to see if the IP address is within the given subnet?
If not, how can it be done? Bit manipulation, I guess?
Using the answers from Thomas and Chris together with Ciscos Subnetting Examples I finally got something to work for IPv4 and IPv6 if you use the CIDR notation (IPAddress/PrefixLength). My IPv6-Implementation might be a bit too straight forward but as there is no UInt128-datatype I couldn't adapt Thomas's solution. Here is the code that seems to work well:
public static bool IsInSubnet(this IPAddress address, string subnetMask)
{
var slashIdx = subnetMask.IndexOf("/");
if (!subnetMask.Contains("/"))
{ // We only handle netmasks in format "IP/PrefixLength".
throw new NotSupportedException("Only SubNetMasks with a given prefix length are supported.");
}
// First parse the address of the netmask before the prefix length.
var maskAddress = IPAddress.Parse(subnetMask.Substring(0, slashIdx));
if (maskAddress.AddressFamily != address.AddressFamily)
{ // We got something like an IPV4-Address for an IPv6-Mask. This is not valid.
return false;
}
// Now find out how long the prefix is.
int maskLength = int.Parse(subnetMask.Substring(slashIdx + 1));
if (maskAddress.AddressFamily == AddressFamily.InterNetwork)
{
// Convert the mask address to an unsigned integer.
var maskAddressBits = BitConverter.ToUInt32(maskAddress.GetAddressBytes().Reverse().ToArray());
// And convert the IpAddress to an unsigned integer.
var ipAdressBits = BitConverter.ToUInt32(address.GetAddressBytes().Reverse().ToArray());
// Get the mask/network address as unsigned integer.
uint mask = uint.MaxValue << (32 - maskLength);
// https://stackoverflow.com/a/1499284/3085985
// Bitwise AND mask and MaskAddress, this should be the same as mask and IpAddress
// as the end of the mask is 0000 which leads to both addresses to end with 0000
// and to start with the prefix.
return (maskAddressBits & mask) == (ipAdressBits & mask);
}
if (maskAddress.AddressFamily == AddressFamily.InterNetworkV6)
{
// Convert the mask address to a BitArray.
var maskAddressBits = new BitArray(maskAddress.GetAddressBytes());
// And convert the IpAddress to a BitArray.
var ipAdressBits = new BitArray(address.GetAddressBytes());
if (maskAddressBits.Length != ipAdressBits.Length)
{
throw new ArgumentException("Length of IP Address and Subnet Mask do not match.");
}
// Compare the prefix bits.
for (int i = 0; i < maskLength; i++)
{
if (ipAdressBits[i] != maskAddressBits[i])
{
return false;
}
}
return true;
}
throw new NotSupportedException("Only InterNetworkV6 or InterNetwork address families are supported.");
}
And this are the XUnit tests I tested it with:
public class IpAddressExtensionsTests
{
[Theory]
[InlineData("192.168.5.85/24", "192.168.5.1")]
[InlineData("192.168.5.85/24", "192.168.5.254")]
[InlineData("10.128.240.50/30", "10.128.240.48")]
[InlineData("10.128.240.50/30", "10.128.240.49")]
[InlineData("10.128.240.50/30", "10.128.240.50")]
[InlineData("10.128.240.50/30", "10.128.240.51")]
public void IpV4SubnetMaskMatchesValidIpAddress(string netMask, string ipAddress)
{
var ipAddressObj = IPAddress.Parse(ipAddress);
Assert.True(ipAddressObj.IsInSubnet(netMask));
}
[Theory]
[InlineData("192.168.5.85/24", "192.168.4.254")]
[InlineData("192.168.5.85/24", "191.168.5.254")]
[InlineData("10.128.240.50/30", "10.128.240.47")]
[InlineData("10.128.240.50/30", "10.128.240.52")]
[InlineData("10.128.240.50/30", "10.128.239.50")]
[InlineData("10.128.240.50/30", "10.127.240.51")]
public void IpV4SubnetMaskDoesNotMatchInvalidIpAddress(string netMask, string ipAddress)
{
var ipAddressObj = IPAddress.Parse(ipAddress);
Assert.False(ipAddressObj.IsInSubnet(netMask));
}
[Theory]
[InlineData("2001:db8:abcd:0012::0/64", "2001:0DB8:ABCD:0012:0000:0000:0000:0000")]
[InlineData("2001:db8:abcd:0012::0/64", "2001:0DB8:ABCD:0012:FFFF:FFFF:FFFF:FFFF")]
[InlineData("2001:db8:abcd:0012::0/64", "2001:0DB8:ABCD:0012:0001:0000:0000:0000")]
[InlineData("2001:db8:abcd:0012::0/64", "2001:0DB8:ABCD:0012:FFFF:FFFF:FFFF:FFF0")]
[InlineData("2001:db8:abcd:0012::0/128", "2001:0DB8:ABCD:0012:0000:0000:0000:0000")]
public void IpV6SubnetMaskMatchesValidIpAddress(string netMask, string ipAddress)
{
var ipAddressObj = IPAddress.Parse(ipAddress);
Assert.True(ipAddressObj.IsInSubnet(netMask));
}
[Theory]
[InlineData("2001:db8:abcd:0012::0/64", "2001:0DB8:ABCD:0011:FFFF:FFFF:FFFF:FFFF")]
[InlineData("2001:db8:abcd:0012::0/64", "2001:0DB8:ABCD:0013:0000:0000:0000:0000")]
[InlineData("2001:db8:abcd:0012::0/64", "2001:0DB8:ABCD:0013:0001:0000:0000:0000")]
[InlineData("2001:db8:abcd:0012::0/64", "2001:0DB8:ABCD:0011:FFFF:FFFF:FFFF:FFF0")]
[InlineData("2001:db8:abcd:0012::0/128", "2001:0DB8:ABCD:0012:0000:0000:0000:0001")]
public void IpV6SubnetMaskDoesNotMatchInvalidIpAddress(string netMask, string ipAddress)
{
var ipAddressObj = IPAddress.Parse(ipAddress);
Assert.False(ipAddressObj.IsInSubnet(netMask));
}
}
As base for the tests I used Ciscos Subnetting Examples and IBMs IPV6 address examples.
I hope someone finds this helpful ;)
Take a look at IP Address Calculations with C# on MSDN blogs. It contains an extension method (IsInSameSubnet) that should meet your needs as well as some other goodies.
public static class IPAddressExtensions
{
public static IPAddress GetBroadcastAddress(this IPAddress address, IPAddress subnetMask)
{
byte[] ipAdressBytes = address.GetAddressBytes();
byte[] subnetMaskBytes = subnetMask.GetAddressBytes();
if (ipAdressBytes.Length != subnetMaskBytes.Length)
throw new ArgumentException("Lengths of IP address and subnet mask do not match.");
byte[] broadcastAddress = new byte[ipAdressBytes.Length];
for (int i = 0; i < broadcastAddress.Length; i++)
{
broadcastAddress[i] = (byte)(ipAdressBytes[i] | (subnetMaskBytes[i] ^ 255));
}
return new IPAddress(broadcastAddress);
}
public static IPAddress GetNetworkAddress(this IPAddress address, IPAddress subnetMask)
{
byte[] ipAdressBytes = address.GetAddressBytes();
byte[] subnetMaskBytes = subnetMask.GetAddressBytes();
if (ipAdressBytes.Length != subnetMaskBytes.Length)
throw new ArgumentException("Lengths of IP address and subnet mask do not match.");
byte[] broadcastAddress = new byte[ipAdressBytes.Length];
for (int i = 0; i < broadcastAddress.Length; i++)
{
broadcastAddress[i] = (byte)(ipAdressBytes[i] & (subnetMaskBytes[i]));
}
return new IPAddress(broadcastAddress);
}
public static bool IsInSameSubnet(this IPAddress address2, IPAddress address, IPAddress subnetMask)
{
IPAddress network1 = address.GetNetworkAddress(subnetMask);
IPAddress network2 = address2.GetNetworkAddress(subnetMask);
return network1.Equals(network2);
}
}
Bit manipulation works. Stuff the IP into a 32-bits unsigned integer, do the same with the subnet's address, &-mask both with 0xFFFFFFFF << (32-20) and compare:
unsigned int net = ..., ip = ...;
int network_bits = 20;
unsigned int mask = 0xFFFFFFFF << (32 - network_bits);
if ((net & mask) == (ip & mask)) {
// ...
}
Since the MSDN blog code relies on a broadcast and IPv6 doesn't have one, I don't know if it works with IPv6.
I ended up with these methods (thanks to nu everest). You can get the subnet and mask from a CIDR notation ("1.2.3.4/5") and check whether an adress is within this network or not.
This works for IPv4 and IPv6:
public static class IpAddresses
{
public static Tuple<IPAddress, IPAddress> GetSubnetAndMaskFromCidr(string cidr)
{
var delimiterIndex = cidr.IndexOf('/');
string ipSubnet = cidr.Substring(0, delimiterIndex);
string mask = cidr.Substring(delimiterIndex + 1);
var subnetAddress = IPAddress.Parse(ipSubnet);
if (subnetAddress.AddressFamily == AddressFamily.InterNetworkV6)
{
// ipv6
var ip = BigInteger.Parse("00FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF", NumberStyles.HexNumber) << (128 - int.Parse(mask));
var maskBytes = new[]
{
(byte)((ip & BigInteger.Parse("00FF000000000000000000000000000000", NumberStyles.HexNumber)) >> 120),
(byte)((ip & BigInteger.Parse("0000FF0000000000000000000000000000", NumberStyles.HexNumber)) >> 112),
(byte)((ip & BigInteger.Parse("000000FF00000000000000000000000000", NumberStyles.HexNumber)) >> 104),
(byte)((ip & BigInteger.Parse("00000000FF000000000000000000000000", NumberStyles.HexNumber)) >> 96),
(byte)((ip & BigInteger.Parse("0000000000FF0000000000000000000000", NumberStyles.HexNumber)) >> 88),
(byte)((ip & BigInteger.Parse("000000000000FF00000000000000000000", NumberStyles.HexNumber)) >> 80),
(byte)((ip & BigInteger.Parse("00000000000000FF000000000000000000", NumberStyles.HexNumber)) >> 72),
(byte)((ip & BigInteger.Parse("0000000000000000FF0000000000000000", NumberStyles.HexNumber)) >> 64),
(byte)((ip & BigInteger.Parse("000000000000000000FF00000000000000", NumberStyles.HexNumber)) >> 56),
(byte)((ip & BigInteger.Parse("00000000000000000000FF000000000000", NumberStyles.HexNumber)) >> 48),
(byte)((ip & BigInteger.Parse("0000000000000000000000FF0000000000", NumberStyles.HexNumber)) >> 40),
(byte)((ip & BigInteger.Parse("000000000000000000000000FF00000000", NumberStyles.HexNumber)) >> 32),
(byte)((ip & BigInteger.Parse("00000000000000000000000000FF000000", NumberStyles.HexNumber)) >> 24),
(byte)((ip & BigInteger.Parse("0000000000000000000000000000FF0000", NumberStyles.HexNumber)) >> 16),
(byte)((ip & BigInteger.Parse("000000000000000000000000000000FF00", NumberStyles.HexNumber)) >> 8),
(byte)((ip & BigInteger.Parse("00000000000000000000000000000000FF", NumberStyles.HexNumber)) >> 0),
};
return Tuple.Create(subnetAddress, new IPAddress(maskBytes));
}
else
{
// ipv4
uint ip = 0xFFFFFFFF << (32 - int.Parse(mask));
var maskBytes = new[]
{
(byte)((ip & 0xFF000000) >> 24),
(byte)((ip & 0x00FF0000) >> 16),
(byte)((ip & 0x0000FF00) >> 8),
(byte)((ip & 0x000000FF) >> 0),
};
return Tuple.Create(subnetAddress, new IPAddress(maskBytes));
}
}
public static bool IsAddressOnSubnet(IPAddress address, IPAddress subnet, IPAddress mask)
{
byte[] addressOctets = address.GetAddressBytes();
byte[] subnetOctets = mask.GetAddressBytes();
byte[] networkOctets = subnet.GetAddressBytes();
// ensure that IPv4 isn't mixed with IPv6
if (addressOctets.Length != subnetOctets.Length
|| addressOctets.Length != networkOctets.Length)
{
return false;
}
for (int i = 0; i < addressOctets.Length; i += 1)
{
var addressOctet = addressOctets[i];
var subnetOctet = subnetOctets[i];
var networkOctet = networkOctets[i];
if (networkOctet != (addressOctet & subnetOctet))
{
return false;
}
}
return true;
}
}
Example usage:
var subnetAndMask = IpAddresses.GetSubnetAndMaskFromCidr("10.132.0.0/20");
bool result = IpAddresses.IsAddressOnSubnet(
IPAddress.Parse("10.132.12.34"),
subnetAndMask.Item1,
subnetAndMask.Item2);
I'm late to the party here, but had a similar need, and put together a quick package to do exactly this.
https://www.nuget.org/packages/IpMatcher/
and source:
https://github.com/jchristn/IpMatcher
Simple use:
using IpMatcher;
Matcher matcher = new Matcher();
matcher.Add("192.168.1.0", "255.255.255.0");
matcher.Add("192.168.2.0", "255.255.255.0");
matcher.Remove("192.168.2.0");
matcher.Exists("192.168.1.0", "255.255.255.0"); // true
matcher.Match("192.168.1.34"); // true
matcher.Match("10.10.10.10"); // false
The solution is to convert the IP Address into bytes using System.Net.IPAddress and perform bitwise comparisons on the address, subnet, and mask octets.
The Binary AND Operator & copies a bit to the result if it exists in both operands.
The code:
using System.Net; // Used to access IPAddress
bool IsAddressOnSubnet(string address, string subnet, string mask)
{
try
{
IPAddress Address = IPAddress.Parse(address);
IPAddress Subnet = IPAddress.Parse(subnet);
IPAddress Mask = IPAddress.Parse(mask);
Byte[] addressOctets = Address.GetAddressBytes();
Byte[] subnetOctets = Mask.GetAddressBytes();
Byte[] networkOctets = Subnet.GetAddressBytes();
return
((networkOctets[0] & subnetOctets[0]) == (addressOctets[0] & subnetOctets[0])) &&
((networkOctets[1] & subnetOctets[1]) == (addressOctets[1] & subnetOctets[1])) &&
((networkOctets[2] & subnetOctets[2]) == (addressOctets[2] & subnetOctets[2])) &&
((networkOctets[3] & subnetOctets[3]) == (addressOctets[3] & subnetOctets[3]));
}
catch (System.Exception ex)
{
return false;
}
}
Special Thanks to Спасибо! Прекрасное решение! Reference
来源：https://stackoverflow.com/questions/1499269/how-to-check-if-an-ip-address-is-within-a-particular-subnet