When you set up directory assistance for an Domino® Directory or Extended Directory Catalog, on the Replicas tab of the Directory Assistance document you specify the replicas of the directory for directory assistance to use. When you specify replicas in a Directory Assistance document for a Domino Directory or Extended Directory Catalog:

• Configure directory failover, so that if one replica is unavailable, directory assistance has at least one alternate replica it can try to use. Directory assistance can use one of two methods to fail over to an alternate replica of a Domino Directory or Extended Directory Catalog: directory assistance failover, the failover method also available in previous releases, or cluster failover.
• Make sure servers that use the directory assistance database have fast network access to the directory replicas you specify. Fast network access to replicas is particularly important if servers use a directory to look up groups for database authorization.
• Make sure servers that do remote lookups to a replica have access to the server that stores the replica, and have at least Reader access in the directory access control list (ACL).
• If a directory is used for Notes® mail addressing, make sure the Notes users that use the feature have at least Reader access in the directory ACL, so they can browse the directory. If Extended Access is enabled for a directory, then the users must also have at least Reader access to use typeahead or F9 address resolution.

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Servers can use the directory assistance failover method, rather than cluster failover method, to find an available replica of a Domino Directory or Extended Directory Catalog. To use the directory assistance failover method, on the Replicas tab of the Directory Assistance document for the directory, specify up to five replicas of the directory that are potentially available for use.

When a server starts up, directory assistance searches for an available replica among the replicas you have specified. If directory assistance cannot find an available replica during server startup, in five minutes it attempts to locate an available replica again, continuing this attempt at five-minute intervals until successful.

Once directory assistance finds an available replica at server startup, it continues to use the replica unless the replica becomes unavailable, at which point failover occurs and directory assistance looks for an alternate replica. When a replica is unavailable for any reason, directory assistance continues to use the alternate replica, even after the previously unavailable replica becomes available.

Directory assistance finds that a replica is unavailable if it attempts to access the replica during server startup, or during normal server operation when it processes a client lookup request. A directory replica is unavailable to directory assistance if:

• The server that stores the replica is unavailable, for example, the server is down or there is a network connectivity problem.
• A view in the replica required for directory lookups is locked because the server that stores the replica is rebuilding the view.
• A replica no longer exists because it has been deleted.

At server startup and during failover, directory assistance looks for an available replica from the list of replicas specified in the Directory Assistance document as follows:

Procedure

1. Looks for a local replica.

2. Looks for a replica within the same Notes named network; if there is more than one, looks in the order in which the Directory Assistance document lists them.

3. Looks for a replica within the same Domino Domain; if there is more than one, looks in the order in which the Directory Assistance document lists them.

4. Looks for a replica it hasn't looked for yet.

The cluster failover method for directory assistance

If the directory assistance database is configured to use a Domino Directory or Extended Directory Catalog that is replicated among servers in a cluster, then you can use cluster failover and workload balancing in place of directory assistance failover.

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To use cluster failover and workload balancing, in the Replicas tab of the Directory Assistance document for the directory specify only one of the directory replicas that is within the cluster. Be sure to specify only one replica; if you specify more than one, directory assistance ignores cluster failover, and instead uses the directory assistance failover method to find an available replica.

Cluster failover is particularly useful in environments with centralized directory services. For example, you can configure cluster failover in a Directory Assistance document for a remote primary Domino Directory, so that servers with Configuration Directories use cluster failover to find an available replica of the remote primary directory.

Related concepts
Directory assistance and failover for a directory
Using a central directory architecture in a Domino domain
Setting up directory assistance
The database access control list
Using cross-certificates to access servers and send secure S/MIME messages
Enabling extended access
Directory assistance concepts

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