C# - How can I identify which IP addresses in a list belong to a specific subnet?

I have a large dynamic list of IP Addresses, their subnet masks, and a given set of subnets. I need some code to be able to identify which subnet each address is on. I'm keeping this fairly vag开发者_高级运维ue because I'm open to many different solutions. Does anybody have some code in C# that can do something similar to this? Thanks!

First, you need code to mask an address to its subnet:

public IPAddress ApplyMask(IPAddress address, IPAddress mask) {
    byte[] addressBytes = address.GetAddressBytes();
    byte[] maskBytes = mask.GetAddressBytes();
    var appliedMaskBytes =
        addressBytes.Zip(
            maskBytes,
            (addressByte, maskByte) => (byte)(addressByte & maskByte)
        )
        .ToArray();
    return new IPAddress(appliedMaskBytes);
}

Then, assuming you have a Dictionary<IPAddress, IPAddress> from an IP address to its mask:

IDictionary<IPAddress, IPAddress> maskDictionary;
var masked = ipAddresses
                 .Select(ipAddress => 
                     new { IPAddress = ipAddress,
                           Subnet = ApplyMask(
                               ipAddress,
                               maskDictionary[ipAddress]
                           )
                     }
                 )
                 .GroupBy(x => x.Subnet);

Now you have a list of address by subnet. Proceed accordingly.

(Note: I don't have compiler handy. Sorry for minor compiler errors.)

You don't need the list of subnets - they can be inferred. You can do it with some bitwise math:

// Key is {Subnet, Subnet Mask}.
// Value is list of IPs in that range.
public static IDictionary<Tuple<IPAddress, IPAddress>, ISet<IPAddress>> AllocateToSubnets(IEnumerable<Tuple<IPAddress, IPAddress>> ips)
{
    var dic = new Dictionary<Tuple<IPAddress, IPAddress>, ISet<IPAddress>>();
    foreach (var item in ips)
    {
        var subnet = Tuple.Create(GetSubnetAddress(item.Item1, item.Item2), item.Item2);

        ISet<IPAddress> set;
        if (!dic.TryGetValue(subnet, out set))
            dic.Add(subnet, set = new HashSet<IPAddress>());
        if (!set.Add(item.Item1))
        {
            // Throw an error if you are looking for duplicates.
        }
    }

    return dic;
}

private static IPAddress GetSubnetAddress(IPAddress address, IPAddress mask)
{
    var b1 = address.GetAddressBytes();
    var b2 = mask.GetAddressBytes();
    if (b1.Length != b2.Length)
        throw new InvalidOperationException("IPAddress and its mask do not share the same family.");
    for (var i = 0; i < b1.Length; i++)
        b1[i] &= b2[i];
    return new IPAddress(b1);
}

Test code:

var ips = new[]
    {
        Tuple.Create(IPAddress.Parse("192.168.0.1"), IPAddress.Parse("255.255.255.0")),
        Tuple.Create(IPAddress.Parse("192.168.0.1"), IPAddress.Parse("255.255.0.0")),
        Tuple.Create(IPAddress.Parse("192.168.0.2"), IPAddress.Parse("255.255.255.0")),
        Tuple.Create(IPAddress.Parse("192.168.0.10"), IPAddress.Parse("255.255.255.0")),
        Tuple.Create(IPAddress.Parse("192.168.0.10"), IPAddress.Parse("255.255.0.0")),
        Tuple.Create(IPAddress.Parse("10.0.0.1"), IPAddress.Parse("255.255.255.0")),
        Tuple.Create(IPAddress.Parse("10.1.0.1"), IPAddress.Parse("255.255.0.0")),
        Tuple.Create(IPAddress.Parse("10.0.0.2"), IPAddress.Parse("255.255.255.0")),
        Tuple.Create(IPAddress.Parse("10.1.0.10"), IPAddress.Parse("255.255.255.0")),
        Tuple.Create(IPAddress.Parse("10.1.0.10"), IPAddress.Parse("255.255.0.0")),
    };

var subnets = AllocateToSubnets(ips);

This depends on which for the definition of your subnets has. If it's an IP address range you can use: Easiest way to check ip address against a range of values using c#

If it's a mask you can use ip&(~mask) to get the lower and ip|(~mask) to get the range and proceed as above.

If the subnet is given with the number of bits the netmask has you can calculate: mask=~(UInt32.MaxValue>>n) and use proceed as above.

If you want to find out the net mask for a given IP, then I have no clue. No idea about IPv6 either.