func ParseCIDR(v string) (*CIDR, error) {
	ip, ipnet, err := net.ParseCIDR(v)
	if err != nil {
		return nil, trace.BadParameter("failed to parse CIDR(%v): %v", v, err.Error())
	}
	return &CIDR{val: v, ip: ip, ipnet: *ipnet}, nil
}
ParseCIDR parses value of the CIDR from string
package configure
import (
	"net"
	"github.com/gravitational/trace"
	"gopkg.in/alecthomas/kingpin.v2"
)
func CIDRFlag(s kingpin.Settings) *CIDR {
	vars := new(CIDR)
	s.SetValue(vars)
	return vars
}