Recovery Manager for AD Forest Edition 10.3.2 - User Guide

Backing up domain controllers

To restore domain controllers, you can use backups created with Recovery Manager for Active Directory. For this reason, you should back up domain controllers in the forest on a regular basis using one of these applications.

It is a good practice to create a Computer Collection that includes all domain controllers in the forest and back up the Collection each time you make changes to the forest infrastructure. Besides, you can use the Computer Collection to ensure that Forest Recovery Agent is installed on each domain controller in the Collection.

For more information about using the Forest Recovery Agent and Computer Collections, see the User Guide supplied with this release of Recovery Manager for Active Directory.

Assigning a preferred DNS server during recovery

Before starting a forest recovery operation, you should specify a method for selecting a preferred DNS server for each domain controller in your recovery project.

Select the General tab, then at the bottom see Additional Setting | Preferred DNS and click on the Change button.

You can choose one of the following DNS server selection methods:

• Select a DNS server automatically
  Let Recovery Manager for Active Directory automatically select a DNS server (used by default).

• Do not change DNS settings
  Recovery Manager for Active Directory retains client DNS settings during recovery or restores the DNS settings from a backup depending on the chosen recovery method.

• Use the specified DNS server
  Specify a DNS server manually - here you can specify one DNS address or a list of DNS servers separated by semicolons or using the Edit button.

For more information on how to specify a DNS server selection method, see Domain controller recovery settings and progress.

The automatic DNS selection method is recommended in the following cases:

• Your DNS service is Active Directory-integrated (AD-inegrated DNS service).

• Your DNS service is not Active Directory-integrated (External DNS service) and original DNS servers are available to restored domain controllers.

The type of DNS service used in the environment determines how the automatic method works, see Handling DNS servers during recovery.

The Forest Recovery Console retrieves a list of DNS servers used previously by domain controllers. For Restore Active Directory on Clean OS and Restore Active Directory® from backup the DNS servers are retrieved from the computer settings that are stored in the backup.

In case of external DNS service, when a new DNS server is used during recovery, then it's recommended to specify the external DNS service IP address as the preferred DNS server for all domain controllers.

When original DNS servers are available then automatic DNS selection uses ordered list of original DNS servers. First the IP addresses that are included in the DNS client settings on this domain controller. Then, the list includes preferred DNS addresses of other domain controllers in the same domain and their DNS client settings. Then, the same approach is used for domain controllers in the parent domain hierarchy, then in child domains, and for direct child domains. Then, during recovery, RMAD automatically selects a properly working DNS server from the received list and assigns that DNS server to the domain controller.

For Active Directory-integrated DNS (AD-integrated DNS), the Primary DNS server has precedence over any previously used DNS server, see Handling DNS servers during recovery. Additional DNS servers are choosen from ordered list of original DNS servers. When Repromotion mode is used it is recommended to specify preferred DNS server manually. Automatic DNS selection for Repromotion phase works only if the same project file is used which was saved after forest recovery completed on first phase.

If a domain controller is a DNS server itself, then a loopback address is included in the DNS server list (see the note below).

By default, the number of DNS servers that can be selected automatically is limited to 3. You can change that number using the MaxAutomaticDnsCount property in advanced settings.

The Do not change DNS settings option lets you retain current DNS client settings during recovery. This option is not recommended, unless user absolutely sure that those DNS settings allow for the restored domain controller find any other domain controller(s) in restored forest.

Manual DNS selection method is recommended for External DNS service and for Repromotion mode. You can provide a DNS server or list of DNS servers. You have to make sure you have one or more DNS servers properly configured for working with the domain controllers being recovered. All these DNS servers must support dynamic updates and have DNS zones configured for each domain in the forest you want to recover. Recovery Manager for Active Directory determines if the specified DNS server does not function properly or is inaccessible, and if so automatically selects one or more original DNS servers.

How does RMAD determine that the DNS server is available for use?

Recovery Manager for Active Directory (RMAD) sets a DNS server on all the network adapters on the domain controller and checks if it is enough to register DC Locator resource records and A-type (host) records. If the test succeeds, then this DNS server is set as the preferred DNS server on all network adapters.

Handling DNS servers during recovery

Active Directory® is tightly coupled with the DNS service. Each domain controller registers and constantly updates several Resource Records (RRs) in the DNS service. Each different type of domain controllers registers a separate set of RRs. During the forest recovery process, these records are adjusted by the Forest Recovery Console.

When you configure a Forest Recovery project, keep the DNS infrastructure in mind. From Forest recovery standpoint, there are two types of DNS infrastructure: Active Directory-integrated DNS (AD-integrated DNS) service and external DNS service. Forest Recovery Console automatically detects DNS service type.

In case where an external DNS service is used, any inter domain DNS relations are out of the Forest Recovery Console scope and are not adjusted by the forest recovery process. The process will update all resource records corresponding to recovered domain controllers and remove resource records of not recovered DCs. It is recommended to use same external DNS server address as Preferred DNS server for all domain controllers in project. For details, see Assigning a Preferred DNS server during recovery.

In case of Active Directory-integrated DNS (AD-integrated DNS), ensure that at least one DNS server per zone is restored from backup. The best practice is to restore as many DNS servers as possible from backup.

Forest Recovery Console analyzes the backup data and detects which domain controller was a DNS server and which DNS zones it hosted. During the recovery process any delegations or a conditional forwarder(s) between DNS zones stored in different domains are detected and all these links are restored according IP addresses of restored domain controllers. This is performed during the Configure DNS server step. If a domain is removed from the restored forest, its relation links are removed as well.

Forest Recovery Console elects one DNS server per each DNS zone as the Primary DNS server for that zone. The decision is based on usages of this DNS server in DNS client settings on original and restored domain controllers. Relation links between zones are restored on the Primary DNS servers.

For AD-integrated DNS it is recommended to use Select DNS server automatically option as Preferred DNS server for all domain controllers in project. For details, see Assigning a Preferred DNS server during recovery. The Primary DNS server IP address is assigned to domain controller DNS client settings depends on the forest root DNS zones replication scope. When a forest root zone has forest replication scope set, then the forest root domain Primary DNS server is selected, otherwise the Primary DNS server of the domain is selected. After the recovery completes, the user can use Managing DNS Client Settings tool to reassign the DNS server IP for any restored domain controller.

When the forest recovery project contains several DCs with IP addresses other than the addresses they originally had (re-IPing technique), then its host RRs are adjusted according to its new IP addresses.

• For a DC with the "Reinstall Active Directory" recovery method, if the DC was an AD-integrated DNS server, it will remain as the DNS server after the reinstall.

• For a DC with the "Install Active Directory" recovery method, user can use Install DNS server on the domain controller.

• For DNS servers that have not been restored, its RRs associated with the DNS server are removed. The following RRs are removed where Z is the forest FQDN, X is the domain default NC FQDN, Y is the site name.

• If the forest recovery project contains a DC which is not restored, its RRs are removed from DNS. This is performed during the Clean up DNS records of removed domain controllers step. Note that if some DCs were excluded from the forest recovery process, but still running, and the DNS server accepts non-secure dynamic updates, then such DCs can still register its SRV records. The following RRs are removed where Z is the forest FQDN, X is the default NC FQDN, Y is the site name and G is the NC X's GUID.

Forest recovery approaches

Before you choose one of the recovery approaches described in this section, it is strongly recommended that you read Microsoft’s best-practice paper, Active Directory Forest Recovery Guide.

This section covers the following:

• Recovery approach 1: Restore as many domain controllers from backups as possible

• Recovery approach 2: Restore one domain controller from backup in each domain