Professional Windows Server 1002003 Security A Technical Reference [Electronic resources] نسخه متنی

Backup Policy, Standards, and Procedures

A backup policy provides the information detailing the what, who, when, and where of information system backups. Standards designate the current approved backup programs and methodologies that will be used. Procedures detail the steps that must be taken to fulfill the policies and meet the standards. Refer to your organization's policy, standards, and procedures to determine what must be done accordingly. You should also be knowledgeable of the specifics of Windows Server 2003 backup and restore. You must ensure that your organization's documentation and practices fulfill the requirements stated by Microsoft for full data recovery, and you must also test the procedures to ensure that when you need to recover, you can.

More specifically, if your documentation does not include instructions on backing up system data for Windows systems, especially domain controllers and specialized services, you need to do so. In the interim, you should ensure the correct backup of this data.

Active Directory-Specific Backup Basics

The backup of the Active Directory database and the associated files that are needed to restore Active Directory are included in a system state backup. But the requirements of restoring Active Directory also dictate how old of a backup can be used in a restore. An Active Directory restore requires that the backup used be no older than the Active Directory tombstone lifetime.

An Active Directory tombstone is created when an object in the Active Directory is deleted. This tombstone is replicated throughout the domain and takes the place of the object. This ensures that the change is replicated throughout the domain, and yet prevents use of the object on those domains that have received the change. The tombstone eventually is deleted based on the tombstone lifetime. In a perfect world, the tombstone lifetime would exactly match the period that extends from the moment the object is deleted on one DC to the moment when every DC receives the replicated change. Although it is possible to determine how long it takes for changes to replicate throughout a specific Active Directory environment, this period may vary over time and therefore cannot be accepted as the time it will always take. Therefore, the tombstone lifetime should be set longer than the longest time it takes for changes to the Active Directory to be replicated, and any major change will require an adjustment. The tombstone lifetime is set to 60 days by default.

The tombstone lifetime attribute is part of the enterprise-wide DS config object and is located at CN=Directory Service,CN=Windows NT,CN=Services,CN=Configuraiton,DC=domainname,DC=domainextension. To change the tombstone lifetime, you need to use adsiedit.msc, ldp.exe, or an ADSI script.

If a backup older than the tombstone lifetime must be used in an Active Directory restore, the replica will have objects in its database that no other DC will have. An administrator would have to manually delete each object on the restored DC.

In most environments where a regular backup plan is adopted and enforced, a backup of Active Directory is usually made more frequently than every 60 days. Take care to see that the Active Directory tombstone lifetime is not adjusted arbitrarily or shortened without ensuring that the backup/restore procedures will provide a backup that can be successfully used in an Active Directory restore.

The Part Backup Plays in an Organization's Business Continuity Plan

In addition to operating system and Windows Server 2003 applications and services, a complete backup program includes provisions for all applications and data. A backup program is but one part of a disaster recovery program, which in turn is part of a business continuity plan. A disaster recovery program creates plans and recovery practices for major disasters, such as a flood, fire, system or network compromise, or other major events. It should include provisions for offsite storage of backups as well as plans for recovering information systems at an alternative location. Disaster recovery includes plans for recovery of other critical business systems as well. Business continuity plans include this process and dictate how to return the business from recovery to a continuation of the business in a more normal operational mode, such as rebuilding and returning to the business location or moving to a new one, restoring less essential services such as access to cafeteria lunch menus, and so forth. The book Network Security: The Complete Reference (published by McGraw-Hill Osborne, 2003) contains a good introduction to disaster recovery and business continuity.