Convert IP addresses range to CIDR format and vice versa

Question

I need to convert IP range to CIDR notation and vice versa.I solved that issue by IPNetwork library by the following way :

Conversion from CIDR to range :

    var ip = IPNetwork.Parse("192.168.168.100/24");
    Console.WriteLine(ip.FirstUsable.ToString() + "/" + ip.LastUsable.ToString());

And convertion from range to CIDR :

    IPNetwork network = IPNetwork.Parse("192.168.168.0");
    IPNetwork network2 = IPNetwork.Parse("192.168.168.255"); 
    IPNetwork ipnetwork = IPNetwork.Supernet(network, network2);
    Console.WriteLine(ipnetwork.FirstUsable + "/" + ipnetwork.Cidr);

It seems it could work fine. But when i use custom tools they return a little bit different result.

For 192.168.168.100/24

The IPNetwork lib returns 192.168.168.1 - 192.168.168.254

http://www.ipaddressguide.com/cidr returns 192.168.168.0 - 192.168.168.255

http://ipconvertertools.com/cidr2ipranges returns 192.168.168.1 - 192.168.168.254

http://ip2cidr.com/bulk-ip-to-cidr-converter.php returns

192.168.168.1/32
192.168.168.2/31
192.168.168.4/30
192.168.168.8/29
192.168.168.16/28

when i try to convert 192.168.168.1 - 192.168.168.254 to CIDR . I'm really confused that different tools return different result. Also, my goal is creating of white list for users and check their IP s when they come, so it is a very important issue.

Answer 1

Given the CIDR notation of 192.168.168.100/24:

Network address is 192.168.168.0 
First usable address is 192.168.168.1
Last usable address is 192.168.168.254 
Broadcast address is 192.168.168.255 
Network mask is 255.255.255.0

There is no and cannot be no ambiguity.