code: func isIP4AddrResolvable(fl FieldLevel) bool {
  
  	if !isIPv4(fl) {
  		return false
  	}
  
  	_, err := net.ResolveIPAddr("ip4", fl.Field().String())
  
  	return err == nil
  }
docs: // IsIP4AddrResolvable is the validation function for validating if the field's value is a resolvable ip4 address.