How to see if an IP address belongs inside of a range of IPs using CIDR notation?

Question

Here I have a static reference the ranges I need to check:

private static List Ip_Range = new List()
{
    \"12.144.86.0/23\",
           


        

Answer 1

If you understand the CIDR notation, you can easily do the math in your parse method.

You basically know that an IPv4 address is 32bits long and that the CIDR notation means that the number of bits behind the "/" are the network address bits (ie the masked out bits), therefore the leftover bits are represent the number of hosts in the subnet.

From wikipedia article:

The number of addresses of a subnet defined by the mask or prefix can be calculated as 2address size - prefix size, in which the address size for IPv6 is 128 and 32 for IPv4. For example, in IPv4, a prefix size of /29 gives: 232-29 = 23 = 8 addresses.

So you could (no I'm not going to work out the details for you) convert your addresses into binary and do the binary AND with the given mask (also in binary form), then you have the network address part of the IP address left, which should match with whatever address you're checking against to see if it's in a particular subnet.