using System.Net; //Namespace

//This will retrun True if the input IP is in cidr range

private bool IsInCIDRRange(string ipAddress, string cidr)
        {
            string[] splitDetails = cidr.Split('/');
            int baseAddress = BitConverter.ToInt32(IPAddress.Parse(splitDetails[0]).GetAddressBytes(), 0);
            int address = BitConverter.ToInt32(IPAddress.Parse(ipAddress).GetAddressBytes(), 0);
            int mask = IPAddress.HostToNetworkOrder(-1 << (32 - int.Parse(splitDetails[1])));
            return ((baseAddress & mask) == (address & mask));
        }