Useful when the AD server is not reachable for any reason and you cannot log-in. This option allows a specific user not to disable security on disk and being able to log-in even under networking issues. You can still perform administration tasks under networking issues.
With this option is enabled the plugin will fallback into the Jenkins Internal User Database for the specific user selected when there is a NamingException. The password of this user will be in sync with the Active Directory as it gets updated each time this user logins into the instance.